The embryo becomes a fruit after the formation of what. Difference between fetus and embryo

Pregnancy is a physiological process in which a new organism develops in the uterus, resulting from fertilization. Pregnancy lasts on average 40 weeks (10 obstetric months).

In the intrauterine development of a child, two periods are distinguished:

1. Embryonic(up to 8 weeks of pregnancy inclusive). At this time, the embryo is called an embryo and acquires characteristic human features;
2. Fetal(from 9 weeks until birth). At this time, the embryo is called a fetus.

The growth of a child, the formation of its organs and systems occurs naturally during various periods of intrauterine development, which is subject to the genetic code embedded in the germ cells and fixed in the process of human evolution.

Embryo development in the first obstetric month (1-4 weeks)

First week (days 1-7)

Pregnancy begins from the moment fertilization- fusion of a mature male cell (sperm) and a female egg. This process usually occurs in the ampullary section of the fallopian tube. After a few hours, the fertilized egg begins to divide exponentially and descends fallopian tube into the uterine cavity (this journey takes up to five days).

As a result of division turns out to be a multicellular organism, which is similar to a blackberry (in Latin “morus”), which is why the embryo at this stage is called Morula. Approximately on the 7th day, the morula penetrates the uterine wall (implantation). The villi of the outer cells of the embryo connect with the blood vessels of the uterus, and subsequently the placenta is formed from them. Other outer morula cells give rise to the development of the umbilical cord and membranes. Over time, various tissues and organs of the fetus will develop from the internal cells.

Information At the time of implantation, a woman may have small bloody issues from the genital tract. Such discharge is physiological and does not require treatment.

Second week (8-14 days)

The outer morula cells grow tightly into the lining of the uterus. In the embryo the formation of the umbilical cord and placenta begins, and neural tube, from which the fetal nervous system subsequently develops.

Third week (15-21 days)

The third week of pregnancy is a difficult and important period. At that time important organs and systems begin to form fetus: the rudiments of the respiratory, digestive, circulatory, nervous and excretory systems appear. At the site where the fetal head will soon appear, a wide plate is formed, which will give rise to the brain. On day 21, the baby's heart begins to beat.

Fourth week (22-28 days)

this week laying of fetal organs continues. The rudiments of the intestines, liver, kidneys and lungs are already present. The heart begins to work more intensely and pumps more and more blood through the circulatory system.

From the beginning of the fourth week in the embryo body folds appear, and appears vertebral primordium(chord).

Completed by day 25 neural tube formation.

By the end of the week (approximately 27-28 days) the muscular system and spine are formed, which divides the embryo into two symmetrical halves, both the upper and lower limbs.

During this period it begins formation of pits on the head, which will later become the eyes of the fetus.

Development of the embryo in the second obstetric month (5-8 weeks)

Fifth week (29-35 days)

During this period the embryo weighs about 0.4 grams, length 1.5-2.5 mm.

The formation of the following organs and systems begins:

1. Digestive system: liver and pancreas;
2. Respiratory system: larynx, trachea, lungs;
3. Circulatory system;
4. Reproductive system: precursors of germ cells are formed;
5. Sense organs: the formation of the eyes and inner ear continues;
6. Nervous system: the formation of parts of the brain begins.

At that time a faint umbilical cord appears. The formation of limbs continues, the first rudiments of nails appear.

On the face the upper lip and nasal cavities are formed.

Sixth week (36-42 days)

Length embryo during this period is about 4-5 mm.

Starts in the sixth week formation of the placenta. At this stage, it is just beginning to function; blood circulation between it and the embryo has not yet been formed.

Ongoing formation brain and its departments. At the sixth week, when performing an encephalogram, it is already possible to record signals from the fetal brain.

Begins formation of facial muscles. The fetal eyes are already more pronounced and uncovered by eyelids that are just beginning to form.

During this period they begin upper limbs change: they lengthen and the rudiments of hands and fingers appear. The lower limbs still remain in their infancy.

Changes in important organs occur:

1. Heart. The division into chambers is completed: ventricles and atria;
2. Urinary system. Primary kidneys have formed, the development of the ureters begins;
3. Digestive system. The formation of sections of the gastrointestinal tract begins: the stomach, small and large intestines. The liver and pancreas had practically completed their development by this period;

Seventh week (43-49 days)

The seventh week is significant in that it is finally The formation of the umbilical cord is completed and uteroplacental circulation is established. Now the breathing and nutrition of the fetus will be carried out due to blood circulation through the vessels of the umbilical cord and placenta.

The embryo is still bent in an arched manner; there is a small tail on the pelvic part of the body. The size of the head is at least half of the embryo. The length from the crown to the sacrum increases by the end of the week up to 13-15 mm.

Ongoing upper limb development. The fingers are visible quite clearly, but their separation from each other has not yet occurred. The child begins to perform spontaneous movements with his hands in response to stimuli.

Fine eyes are formed, already covered with eyelids, which protect them from drying out. The child can open his mouth.

The formation of the nasal fold and nose occurs, two paired elevations are formed on the sides of the head, from which they will begin to develop ears.

Intensive continues development of the brain and its parts.

Eighth week (50-56 days)

The body of the embryo begins to straighten, length from the crown to the coccyx is 15 mm at the beginning of the week and 20-21 mm on day 56.

Ongoing formation of important organs and systems: digestive system, heart, lungs, brain, urinary system, reproductive system(boys develop testicles). The hearing organs are developing.

By the end of the eighth week the child's face becomes familiar to the person: the eyes are well defined, covered with eyelids, the nose, the ears, the formation of the lips is ending.

Intensive growth of the head, upper and lower horses is noted In particular, ossification of the long bones of the arms and legs and the skull develops. The fingers are clearly visible; there is no skin membrane between them.

Additionally At eight weeks the embryonic period of development ends and the fetal period begins. From this time on, the embryo is called a fetus.

Fetal development in the third obstetric month (9-12 weeks)

Ninth week (57-63 days)

At the beginning of the ninth week coccygeal-parietal size fetus is about 22 mm, by the end of the week - 31 mm.

Happening improvement of blood vessels of the placenta, which improves uteroplacental blood flow.

The development of the musculoskeletal system continues. The process of ossification begins, the joints of the toes and hands are formed. The fetus begins to make active movements and can clench its fingers. The head is lowered, the chin is pressed tightly to the chest.

Changes occur in the cardiovascular system. The heart beats up to 150 times per minute and pumps blood through its blood vessels. The composition of blood is still very different from the blood of an adult: it consists only of red blood cells.

Ongoing further growth and development of the brain, cerebellar structures are formed.

The organs of the endocrine system are intensively developing, in particular, the adrenal glands, which produce important hormones.

Improves cartilage tissue: auricles, laryngeal cartilages, vocal cords are being formed.

Tenth week (64-70 days)

By the end of the tenth week fruit length from the coccyx to the crown is 35-40 mm.

Buttocks begin to develop, the previously existing tail disappears. The fetus is in the uterus in a fairly free position in a semi-bent state.

Nervous system development continues. Now the fetus performs not only chaotic movements, but also reflex ones in response to a stimulus. When accidentally touching the walls of the uterus, the child makes movements in response: turns his head, bends or straightens his arms and legs, and pushes to the side. The size of the fetus is still very small, and the woman cannot yet feel these movements.

The sucking reflex is formed, the child begins reflex movements with his lips.

The development of the diaphragm is completed, which will take an active part in breathing.

Eleventh week (71-77 days)

By the end of this week coccygeal-parietal size the fetus increases to 4-5 cm.

The fetal body remains disproportionate: small body, large head, long arms and short legs, bent at all joints and pressed to the stomach.

The placenta has already reached sufficient development and copes with its functions: ensures the supply of oxygen and nutrients to the fetus and removes carbon dioxide and products of exchange.

Further formation of the fetal eyes occurs: At this time, the iris develops, which will later determine the color of the eyes. The eyes are well developed, half-closed or wide open.

Twelfth week (78-84 days)

Coccygeal-parietal size fetus is 50-60 mm.

Goes clearly development of the genital organs according to the female or male type.

Happening further improvement of the digestive system. The intestines are elongated and arranged in loops, like those of an adult. Its periodic contractions begin - peristalsis. The fetus begins to make swallowing movements, swallowing amniotic fluid.

The development and improvement of the fetal nervous system continues. The brain is small in size, but exactly replicates all the structures of the adult brain. The cerebral hemispheres and other sections are well developed. Reflex movements are improved: the fetus can clench and unclench its fingers into a fist, grabs thumb and actively sucks it.

In fetal blood Not only red blood cells are already present, but the production of white blood cells - leukocytes - also begins.

At this time the child single respiratory movements begin to be recorded. Before birth, the fetus cannot breathe, its lungs do not function, but it makes rhythmic movements of the chest, imitating breathing.

By the end of the week the fetus eyebrows and eyelashes appear, the neck is clearly visible.

Fetal development in the fourth obstetric month (13-16 weeks)

Week 13 (85-91 days)

Coccygeal-parietal size by the end of the week is 70-75 mm. The proportions of the body begin to change: the upper and lower limbs and torso lengthen, the size of the head is no longer so large in relation to the body.

Improvement of the digestive and nervous systems continues. The embryos of baby teeth begin to appear under the upper and lower jaws.

The face is fully formed, the ears, nose and eyes are clearly visible (the eyelids are completely closed).

Week 14 (92-98 days)

Coccygeal-parietal size by the end of the fourteenth week it increases up to 8-9 cm. Body proportions continue to change to more familiar ones. The face has a well-defined forehead, nose, cheeks and chin. The first hair appears on the head (very thin and colorless). The surface of the body is covered with vellus hairs, which retain skin lubrication and thereby perform protective functions.

The musculoskeletal system of the fetus is improved. Bones become stronger. Motor activity increases: the fetus can turn over, bend, and make swimming movements.

Development of the kidneys, bladder and ureters is complete. The kidneys begin to secrete urine, which mixes with the amniotic fluid.

: pancreatic cells begin to work, producing insulin, and pituitary cells.

Changes in the genital organs appear. In boys, the prostate gland forms; in girls, the ovaries migrate into the pelvic cavity. At the fourteenth week, with a good sensitive ultrasound machine, it is already possible to determine the sex of the child.

Fifteenth week (99-105 days)

Coccygeal-parietal size of the fetus is about 10 cm, fruit weight – 70-75 grams. The head still remains quite large, but the growth of the arms, legs and torso begins to outstrip it.

The circulatory system is improved. In the fourth month, a child’s blood type and Rh factor can already be determined. Blood vessels (veins, arteries, capillaries) grow in length and their walls become stronger.

The production of original feces (meconium) begins. This is due to the ingestion of amniotic fluid, which enters the stomach, then into the intestines and fills it.

Fully formed fingers and toes, an individual design appears on them.

Sixteenth week (106-112 days)

The weight of the fetus increases to 100 grams, the coccygeal-parietal size - up to 12 cm.

By the end of the sixteenth week, the fetus is already fully formed, he has all the organs and systems. The kidneys are actively working, a small amount of urine is released into the amniotic fluid every hour.

The skin of the fetus is very thin, subcutaneous fatty tissue is practically absent, so blood vessels are visible through the skin. The skin appears bright red, covered with vellus hairs and grease. Eyebrows and eyelashes are well defined. Nails are formed, but they only cover the edge of the nail phalanx.

Facial muscles are formed, and the fetus begins to “grimace”: frowning of the eyebrows and a semblance of a smile are observed.

Fetal development in the fifth obstetric month (17-20 weeks)

Seventeenth week (days 113-119)

The weight of the fetus is 120-150 grams, the coccygeal-parietal size is 14-15 cm.

The skin remains very thin, but subcutaneous fatty tissue begins to develop under it. The development of baby teeth continues, which are covered with dentin. The embryos of permanent teeth begin to form under them.

There is a reaction to sound stimuli. From this week we can say for sure that the child began to hear. When strong sharp sounds appear, the fetus begins to actively move.

Fetal position changes. The head is raised and is in an almost vertical position. The arms are bent at the elbow joints, the fingers are clenched into a fist almost all the time. Periodically, the child begins to suck his thumb.

The heartbeat becomes clear. From now on, the doctor can listen to him using a stethoscope.

Eighteenth week (120-126 days)

The child's weight is about 200 grams, length - up to 20 cm.

The formation of sleep and wakefulness begins. Most of the time the fetus sleeps, movements stop during this time.

At this time, the woman may already begin to feel the baby moving, especially with repeated pregnancies. The first movements are felt as gentle jolts. A woman may feel more active movements when she is nervous or stressed, which affects the emotional state of the child. At this stage, the norm is about ten episodes of fetal movement per day.

Nineteenth week (127-133 days)

The child’s weight increases to 250-300 grams, body length – to 22-23 cm. The proportions of the body change: the head lags behind the body in growth, the arms and legs begin to lengthen.

Movements become more frequent and noticeable. They can be felt not only by the woman herself, but also by other people by placing their hand on their stomach. Primigravidas at this time can only begin to feel movements.

The endocrine system is improved: the pancreas, pituitary gland, adrenal glands, gonads, thyroid and parathyroid glands are actively functioning.

Blood composition has changed: In addition to erythrocytes and leukocytes, the blood contains monocytes and lymphocytes. The spleen begins to take part in hematopoiesis.

Twentieth week (134-140 days)

Body length increases to 23-25 ​​cm, weight – up to 340 grams.

The fetal skin is still thin, covered with protective lubricant and vellus hairs, which can persist until childbirth. Subcutaneous fatty tissue develops intensively.

Well formed eyes, at twenty weeks the blink reflex begins to appear.

Improved movement coordination: The child confidently brings his finger to his mouth and begins to suck it. Facial expressions are pronounced: the fetus may close its eyes, smile, or frown.

This week all women are already feeling movements., regardless of the number of pregnancies. Movement activity varies throughout the day. When stimuli appear (loud sounds, stuffy rooms), the child begins to move very violently and actively.

Fetal development in the sixth obstetric month (21-24 weeks)

Twenty-first week (days 141-147)

Body weight grows to 380 grams, fetal length – up to 27 cm.

The layer of subcutaneous tissue increases. The skin of the fetus is wrinkled, with many folds.

Fetal movements become more active and tangible. The fetus moves freely in the uterine cavity: it lies head down or buttocks, across the uterus. Can pull on the umbilical cord, push off the walls of the uterus with hands and feet.

Changes in sleep and wakefulness patterns. Now the fetus spends less time sleeping (16-20 hours).

Twenty-second week (148-154 days)

At week 22, the size of the fetus increases to 28 cm, weight - up to 450-500 grams. The size of the head becomes proportional to the body and limbs. The legs are bent almost all the time.

The fetal spine is fully formed: It has all the vertebrae, ligaments and joints. The process of strengthening bones continues.

Improves the fetal nervous system: The brain already contains all the nerve cells (neurons) and has a mass of about 100 grams. The child begins to take an interest in his body: he feels his face, arms, legs, tilts his head, brings his fingers to his mouth.

Heart size increases significantly, are improving functionality of cardio-vascular system.

Twenty-third week (155-161 days)

The length of the fetal body is 28-30 cm, weight is about 500 grams. Pigment begins to be synthesized in the skin, resulting in the skin becoming bright red. The subcutaneous fatty tissue is still quite thin, as a result the child looks very thin and wrinkled. The lubricant covers the entire skin and is more abundant in the folds of the body (elbow, axillary, inguinal, etc. folds).

Development of internal genital organs continues: in boys - the scrotum, in girls - the ovaries.

Respiratory frequency increases up to 50-60 times per minute.

The swallowing reflex is still well developed: the child constantly swallows amniotic fluid with particles of protective skin lubricant. The liquid part of the amniotic fluid is absorbed into the blood, leaving a thick green-black substance (meconium) in the intestines. Normally, the bowel should not have a bowel movement until the baby is born. Sometimes swallowing water causes hiccups in the fetus; a woman can feel it in the form of rhythmic movements for several minutes.

Twenty-fourth week (162-168 days)

By the end of this week, the weight of the fetus increases to 600 grams, body length to 30-32 cm.

The movements are becoming stronger and clearer. The fetus takes up almost all the space in the uterus, but can still change position and turn over. Muscles grow rapidly.

By the end of the sixth month, the child has well-developed sense organs. Vision begins to function. If a bright light hits a woman’s belly, the fetus begins to turn away and closes her eyelids tightly. Hearing is well developed. The fetus determines pleasant and unpleasant sounds for itself and reacts to them differently. When hearing pleasant sounds, the child behaves calmly, his movements become calm and measured. When unpleasant sounds occur, it begins to freeze or, conversely, moves very actively.

An emotional connection is established between mother and child. If a woman experiences negative emotions (fear, anxiety, melancholy), the child begins to experience similar feelings.

Fetal development in the seventh obstetric month (25-28 weeks)

Twenty-fifth week (169-175 days)

The length of the fetus is 30-34 cm, body weight increases to 650-700 grams. The skin becomes elastic, the number and severity of folds decreases due to the accumulation of subcutaneous fatty tissue. The skin remains thin with a large number of capillaries, giving it a red color.

The face has a familiar appearance to a person: eyes, eyelids, eyebrows, eyelashes, cheeks, ears are well defined. The cartilage of the ears remains thin and soft, their bends and curls are not fully formed.

Bone marrow develops intensively, which takes on the main role in hematopoiesis. The strengthening of the fetal bones continues.

Important processes occur in lung maturation: small elements of lung tissue (alveoli) are formed. Before the baby is born, they are without air and resemble deflated balloons, which straighten out only after the first cry of the newborn. From week 25, the alveoli begin to produce a special substance (surfactant) necessary to maintain their shape.

Twenty-sixth week (176-182 days)

The length of the fruit is about 35 cm, the weight increases to 750-760 grams. The growth of muscle tissue and subcutaneous fat continues. Bones are strengthened and permanent teeth continue to develop.

The formation of the genital organs continues. In boys, the testicles begin to descend into the scrotum (the process lasts 3-4 weeks). In girls, the formation of the external genitalia and vagina is completed.

Improved sense organs. The child develops a sense of smell (smell).

Twenty-seventh week (183-189 days)

Weight increases to 850 grams, body length - up to 37 cm.

The organs of the endocrine system are actively functioning, in particular the pancreas, pituitary gland and thyroid gland.

The fruit is quite active, makes freely various movements inside the uterus.

From the twenty-seventh week in the child individual metabolism begins to form.

Twenty-eighth week (190-196 days)

The child’s weight increases to 950 grams, body length – 38 cm.

By this age the fetus becomes practically viable. In the absence of organ pathology, a child with good care and treatment can survive.

Subcutaneous fat continues to accumulate. The skin is still red in color, the vellus hair begins to gradually fall out, remaining only on the back and shoulders. Eyebrows, eyelashes, and hair on the head become darker. The child begins to open his eyes frequently. The cartilage of the nose and ears remains soft. The nails do not yet reach the edge of the nail phalanx.

This week starts more one of the cerebral hemispheres is actively functioning. If the right hemisphere becomes active, then the child becomes left-handed; if the left hemisphere becomes active, then right-handedness develops.

Fetal development in the eighth month (29-32 weeks)

Twenty-ninth week (197-203 days)

The weight of the fetus is about 1200 grams, the height increases to 39 cm.

The baby has already grown enough and takes up almost all the space in the uterus. Movements become less chaotic. The movements manifest themselves in the form of periodic kicks with the legs and arms. The fetus begins to take a definite position in the uterus: head or buttocks down.

All organ systems continue to improve. The kidneys already secrete up to 500 ml of urine per day. The load on the cardiovascular system increases. The blood circulation of the fetus is still significantly different from the blood circulation of the newborn.

Thirtieth week (204-210 days)

Body weight increases to 1300-1350 grams, height remains approximately the same - about 38-39 cm.

Subcutaneous fat tissue constantly accumulates, skin folds straighten out. The child adapts to the lack of space and takes a certain position: curls up, arms and legs crossed. The skin still has a bright color, the amount of grease and vellus hair decreases.

Alveolar development and surfactant production continues. The lungs prepare for the birth of the baby and the start of breathing.

Brain development continues brain, the number of convolutions and the area of ​​the cortex increases.

Thirty-first week (211-217 days)

The child's weight is about 1500-1700 grams, height increases to 40 cm.

Your child's sleep and wake patterns change. Sleep still takes a long time, during which time there is no motor activity of the fetus. While awake, the child actively moves and pushes.

Fully formed eyes. During sleep, the child closes his eyes, while awake, the eyes are open, and the child blinks periodically. All children have the same iris color ( blue color), then after birth it begins to change. The fetus reacts to bright light by constricting or dilating the pupil.

Brain size increases. Now its volume is about 25% of the volume of the adult brain.

Thirty-second week (218-224 days)

The child's height is about 42 cm, weight - 1700-1800 grams.

Accumulation of subcutaneous fat continues, due to which the skin becomes lighter, there are practically no folds left on it.

Internal organs are improved: organs of the endocrine system intensively secrete hormones, surfactant accumulates in the lungs.

The fetus produces a special hormone, which promotes the formation of estrogen in the mother’s body, as a result, the mammary glands begin to prepare for milk production.

Fetal development in the ninth month (33-36 weeks)

Thirty-third week (225-231 days)

The weight of the fetus increases to 1900-2000 grams, the height is about 43-44 cm.

Skin becomes increasingly lighter and smoother, the layer of fatty tissue increases. The vellus hair is increasingly wiped off, and the layer of protective lubricant, on the contrary, increases. Nails grow to the edge of the nail phalanx.

The baby becomes increasingly cramped in the uterine cavity, so his movements become more rare, but strong. The position of the fetus is fixed (head or buttocks down), the likelihood that the child will turn over after this period is extremely small.

The functioning of internal organs is becoming more and more improved: the mass of the heart increases, the formation of the alveoli is almost complete, the tone of the blood vessels increases, the brain is fully formed.

Thirty-fourth week (232-238 days)

The child's weight ranges from 2000 to 2500 grams, height is about 44-45 cm.

The baby now occupies a stable position in the uterus. The bones of the skull are soft and mobile thanks to the fontanelles, which can close only a few months after birth.

Head hair grows rapidly and take on a certain color. However, hair color may change after childbirth.

Intensive strengthening of bones is noted, in connection with this, the fetus begins to take calcium from the mother’s body (the woman may notice the appearance of seizures at this time).

The baby constantly swallows amniotic fluid, thereby stimulating the gastrointestinal tract and the functioning of the kidneys, which produce at least 600 ml of clear urine per day.

Thirty-fifth week (239-245 days)

Every day the child gains 25-35 grams. Weight during this period can vary greatly and by the end of the week it is 2200-2700 grams. Height increases to 46 cm.

All internal organs of the child continue to improve, preparing the body for the upcoming extrauterine existence.

Fatty tissue is intensively deposited, the child becomes more well-fed. The amount of vellus hair is greatly reduced. The nails have already reached the tips of the nail phalanges.

A sufficient amount of meconium has already accumulated in the fetal intestines, which normally should go away 6-7 hours after birth.

Thirty-sixth week (246-252 days)

The weight of a child varies greatly and can range from 2000 to 3000 grams, height - within 46-48 cm

The fetus already has well-developed subcutaneous fatty tissue, skin color becomes lighter, wrinkles and folds disappear completely.

The baby occupies a certain position in the uterus: more often he lies upside down (less often, with his legs or buttocks, in some cases, transversely), his head is bent, his chin is pressed to his chest, his arms and legs are pressed to his body.

Skull bones, unlike other bones, remain soft, with cracks (fontanelles), which will allow the baby's head to be more pliable when passing through the birth canal.

All organs and systems are fully developed for the existence of a child outside the womb.

Fetal development in the tenth obstetric month

Thirty-seventh week (254-259 days)

The child's height increases to 48-49 cm, weight can fluctuate significantly. The skin has become lighter and thicker, the fat layer increases every day by 14-15 grams per day.

Cartilages of the nose and ears become denser and more elastic.

Fully lungs are formed and mature, the alveoli contain the necessary amount of surfactant for the newborn to breathe.

The digestive system has matured: Contractions occur in the stomach and intestines to push food through (peristalsis).

Thirty-eighth week (260-266 days)

A child's weight and height vary greatly.

The fetus is fully mature and ready to be born. Externally, the child looks like a full-term newborn. The skin is light, the fatty tissue is sufficiently developed, and vellus hair is practically absent.

Thirty-ninth week (267-273 days)

Typically two weeks before birth the fruit begins to descend, pressing against the pelvic bones. The child has already reached full maturity. The placenta begins to gradually age and its metabolic processes deteriorate.

The weight of the fetus increases significantly (30-35 grams per day). The proportions of the body change completely: the chest and shoulder girdle are well developed, the belly is round, and the limbs are long.

Well developed sense organs: the child catches all sounds, sees bright colors, can focus vision, taste buds are developed.

Fortieth week (274-280 days)

All indicators of fetal development correspond to new to the awaited one. The baby is completely ready for birth. The weight can vary significantly: from 250 to 4000 and above grams.

The uterus begins to periodically contract(), which is manifested by aching pain in the lower abdomen. The cervix opens slightly, and the fetal head is pressed closer to the pelvic cavity.

The skull bones are still soft and pliable, which allows the baby’s head to change shape and pass the birth canal more easily.

Fetal development by week of pregnancy - Video

Before we begin to consider the dynamics of the development of the embryo and fetus, let us say that the concepts of the embryo and the fetus are not identical. A embryo, or otherwise an embryo, is an organism in which its main defining features are just being formed; it is an organism in the period of organogenesis (organ formation).
The human embryo goes through this period within eight weeks from the moment of fertilization. As soon as the body is formed, in which it is already possible to determine the main external morphological characteristics, in which the corresponding internal organization has also developed, we have every reason to talk about the fetus. From the ninth week of intrauterine development inclusive and ending with birth, the embryo is usually called a fetus.
So…
First five days
Soon after fertilization - approximately 12 hours after the fusion of the nuclei of the female and male germ cells - the egg begins to fragment. A fertilized egg is called an egg. Moving along the tube towards the uterine cavity, the egg loses its transparent shell. The fragmentation of the fertilized egg occurs quite actively - two new fragmentations per day. The egg does not have its own mobility; its advancement towards the uterus is possible solely due to three factors: peristaltic contractions of the muscular layer of the fallopian tube, directed movements of the cilia of the ciliated epithelium and the flow of fluid in the fallopian tube. In the case when, for one reason or another, the patency of the fallopian tube is impaired, the egg does not have the opportunity to enter the uterine cavity; however, the egg continues to fragment and grow, and an ectopic, or tubal, pregnancy develops. The term ectopia is also used to refer to ectopic pregnancy, but it has a broader meaning, since, in addition to ectopic tubal pregnancy, pregnancy can develop, although this is extremely rare, in the ovary and even in the abdominal cavity.
Sixth - eighth day.
If the pregnancy proceeds normally, then the egg is released into the uterine cavity around this time. In the mucous membrane of the uterus, under the influence of two hormones: estrogen (follicular hormone) and progesterone (hormone of the corpus luteum), some changes have already occurred by this time, with the goal of creating the most favorable conditions for the development of the embryo; the structure of the uterine mucosa becomes looser. Inoculation of the egg, or implantation, occurs: not far from the exit of the fallopian tubes, the egg settles on the surface of the mucous membrane; then enzyme-like substances are released from the chorionic villi of the egg, which dissolve the mucous membrane, and the egg seems to sink into it; germination of the egg into the mucosa is deep enough so that the defect in the mucous membrane can soon close over the egg. In most cases, the process of egg implantation ends by the fourteenth day from the moment of fertilization.
Second and third weeks
Once under the protection of the uterine mucosa, the embryo continues to actively develop. The frequency of cell divisions in it is the same: divisions follow one after another every X hours. There is a gradual separation of the embryo from the membranes. Increasingly in size, the embryo reaches 2 mm in length by the end of the third week (for comparison: the egg has a diameter of 0.5 mm). The bone, muscle and nervous systems are formed. Around the same time, the heart is formed - in the form of a paired rudiment; after a little time, these rudiments merge and form a slightly curved heart tube. In parallel, the process of laying down large blood vessels is underway. At the same time, the embryo separates its intestines. At this stage of development, the embryo resembles in appearance the larva of some insect, and we have reason to recall the very popular theory that every individual repeats the path of development that its entire species has gone through over millions of years - from single-celled organisms to modern man in all his perfection (isn’t this It’s remarkable that in the ninth week of intrauterine development the tail of a human fetus atrophies? Doesn’t a person, when born, mentally repeat the development of his ancestors from the Cro-Magnon man to our contemporary?); many researchers elevate this theory of “path repetition” to the level of a “basic biokinetic law.”

Fourth week

The embryo grows quite quickly and already reaches a length of 5 mm. The nervous system receives a new impetus for development: the brain tube closes, the brain quickly forms (the main parts of the brain begin to emerge, the formation of the spinal cord occurs) and the spine. The autonomic nervous system is also formed. Large blood vessels undergo further development and close together. The heart begins to become active; It is curious that at this stage of development it has three chambers. The chest is outlined. Primary buds are formed.

Fifth week

The length of the embryo at the fifth week is approximately 6 mm. Slowly the embryo takes shape: characteristic curves of the body appear. You can determine the rudiments of the head, limbs, and tail. There are gill slits. The lungs, liver, and thyroid gland are formed; at this stage of embryo development they have the appearance of hollow invaginations. The jaw processes develop.

Sixth week

The head and spinal column of the embryo can already be easily identified. The abdominal cavity can also be considered formed. The heart and circulatory system are functioning. The limbs of the embryo are short. The hands and feet are still just taking on their shape.

Seventh week

Organogenesis becomes more and more intense. Previously established organs are being improved. The embryo's head, back, chest, abdomen, arms and legs are easily identified. It is semi-transparent. Some organs and large blood vessels can be seen. The embryo floats in the fetal sac, in the amniotic fluid. The heart and blood vessels function more and more confidently. The embryo is connected to the placenta through the umbilical cord. Fingers are visible on the arms and legs; they are short and thick. The rudiments of eyes and ears are just appearing; Moreover, these rudiments are still covered with skin. Gonads appear in the form of genital ridges. The length of a seven-week embryo can be from 12 to 15 mm.

Eighth week

The embryo grows quite quickly. The body is basically formed. The embryo already has all the organs, and many of them have begun to perform their functions. The digestive system consists of the esophagus, stomach, and a thin and winding intestinal tube. The head of the embryo and its body are approximately equal in length. Limbs lengthen. There is a noticeable difference in the structure of the genital organs. The face begins to take shape. The nose, mouth, eyes, and ears are easily distinguishable. The gill slits atrophy. The length of an eight-week embryo is from 20 to 30 mm, weight – 10-13 g.
Ninth week

From now on, we are no longer talking about an embryo or fetus, but about a fetus. The main external morphological characteristics are easily determined. The body gradually increases in size relative to the head. The limbs are still lengthening. The tail atrophies. The face is completely formed. The length of the fruit reaches 30 mm or more.

Tenth week

The fetal body is growing rapidly. Development occurs along the path of further differentiation of internal organs. The eyes of the fetus are easily distinguishable, and a tongue has formed in the oral cavity; hearing continues to develop
- its internal part. Several points of ossification of the skeleton appear. The fetus feels comfortable in the amniotic fluid. In parallel with the development of the fetus, the placenta develops. Medical scientists believe that a fetus, whose age is estimated at ten weeks, is already capable of feeling much of what its mother feels. There is also the following original opinion: at approximately ten weeks of age, the personal foundations of a person are laid.

Eleventh week

The external genitalia of the fetus are clearly visible. Proportionally, the fruit changes quite quickly, but its head is still relatively large, and its arms and legs are short. It should be noted here that the process of changing body proportions is very long and stretches over many years while the body grows - right up to the age of majority; but the intensity of this process changes; During the intrauterine development of the organism, its intensity is very high, then it gradually and steadily decreases.

Twelfth and thirteenth weeks

Many of the developing organs and systems are functioning. By the twelfth week, the fetus is already well established in the uterine cavity, as a result of which the likelihood of miscarriage is significantly reduced. The placenta continues to develop and secretes hormones necessary for the normal course of pregnancy. Through the umbilical cord, the fetus receives blood rich in oxygen and nutrients from the placenta, and metabolic products are removed from the fetus through the umbilical cord. The fetus is already moving a little - slightly bending its limbs. At the twelfth week, the weight of the fetus is about 20 g, at the thirteenth - up to 30 g.

Fourteenth week

The length of the fruit reaches approximately 90 mm. Facial features are easily determined, since the eyes, nose, mouth, and forehead are well expressed. The skin of the fetus is still very thin, and the blood vessels are visible through it - like red threads. Limbs continue to develop; their growth is already noticeable, at least because the fetus is able to easily touch one limb to another; Before this was impossible. Nail rudiments appear on the fingers. The movements of the fetal limbs are becoming more active; the fetus bends and unbends its arms and legs, as if testing its acquired abilities, being surprised and rejoicing at them. However, the mother does not yet feel these movements of the fetus. The gender of the fetus is determined without difficulty.
Fifteenth week

The length of the fruit can already reach 100 mm. The range of movements of the limbs gradually becomes wider.

Sixteenth week

The length of the fetus by the end of the sixteenth week is 150-160 mm, and its weight is up to 120 g. The skin is thin and reddish in color; superficial blood vessels are still visible through the skin - since the subcutaneous fat layer is still practically not developed; The superficial vascular network is especially visible in the area of ​​the temples, neck, back of the fetus, forearms, and thighs. The location of the navel is low (near the pubis). The process of ossification of the skeleton continues; ossification points also appear in the bones of the skull. The muscular system is formed and developed. The fetus not only bends and unbends its arms and legs, but also makes movements that can be called grasping, it grabs the umbilical cord, grabs one arm with another. The fetus sucks its finger. Makes movements similar to breathing - as if he is already preparing to breathe through the lungs. Swallows and also “inhales” (into the upper respiratory tract) amniotic fluid. Since the digestive and excretory systems are already functioning, the swallowed liquid is absorbed in the intestines (meconium is formed from the indigestible residue), and then excreted by the kidneys and thrown out into the amniotic fluid. Some foreign authors claim that a sixteen-week fetus has different facial expressions. An ultrasound scan clearly shows the fetal head, which is already much smaller than the body, arms, legs, and umbilical cord.

Seventeenth week

The growth rate of the fetus is slightly reduced. Development follows the path of improving organs. At the seventeenth week, the length of the fetus is about 180 mm. Movements are becoming more active. Sometimes the fetus hiccups. Swallows amniotic fluid; but not all substances present in it are absorbed in the intestines of the fetus; This is explained by the fact that some enzymes are produced in the fetal body in insufficient quantities. Periodic ingestion of amniotic fluid should not be considered accidental (in the functioning and development of the body, perhaps, there is no place for accident; everything matters, everything can be given a logical explanation); thanks to these ingestions, the digestive and excretory systems develop and prepare for the strongest active activity; these systems seem to learn to function. The fact is that the fetus receives nutrition through amniotic fluid and has of great importance, because amniotic fluid does not meet the needs of patching. As the fetus grows and develops, it ingests everything in the amniotic fluid. Specially slow studies have established that by the end of pregnancy the fetus can swallow more than 400 ml of amniotic fluid per day.
liquids.

Eighteenth and nineteenth weeks

The length of the fetus at this stage of development reaches 200 mm. And the weight is 250-280 g. At times, the fetus actively moves, and the mother already begins to feel its movements. When listening through a tube to a pregnant woman's abdomen, the fetal heartbeat can be heard. Fat begins to slowly accumulate under the skin of the fetus, so the surface blood vessels are almost no longer visible. Although the skin is still quite thin and has a reddish color; gradually it thickens and brightens. The skin of the fetus is covered with very delicate vellus hair. This hair is called lanugo (germinal fuzz). The fetus may also already have hair on its head. The sebaceous glands embedded in the skin begin to become increasingly active. They produce a lubricant, the purpose of which is to protect the skin of the fetus from the effects of amniotic fluid. If the sebaceous glands did not secrete their secretions, the skin of the fetus would undergo maceration. It is curious that the movements of the fetus contribute to the uniform distribution of the secretion of the sebaceous glands over the surface of the skin.
Twentieth week

The length of the fetus can already be up to 260 mm, and the weight can be slightly more than 300 g. During auscultation, the fetal heartbeat can be heard. The skin of the fetus is still reddish. The secretion of the sebaceous glands mixes with the secreted cells of the epidermis, and a cheese-like lubricant is formed; it is also called vernix lubrication. There are significant accumulations of this lubricant on the fetus’s face, as well as on the back and limbs. The cheese-like lubricant gives the skin a whitish tint. The subcutaneous tissue gradually becomes thicker. The fetus continues to occasionally swallow amniotic fluid. This fluid partially covers the fetal body's need for water. Meconium, or original feces, is formed from the undigested residue; Meconium contains not only epidermal scales, vellus hairs (lanugo), but also the secretion of the fetal sebaceous glands, as well as bile. It is with bile that meconium is colored yellow-green or brown (sometimes meconium is green-black).

Twenty-first and twenty-second weeks

Fetal growth accelerates somewhat again. The proportions continue to change gradually. The fruit no longer looks as big-headed as before. The accumulation of subcutaneous fat layer increases. Due to this, the skin becomes less wrinkled. The development of all organs and systems continues. The skin also develops. Two layers are formed in the skin: the epidermis (superficial layer) and the dermis, or skin itself (deeper layer). The fetus develops eyebrows and eyelashes, and its face takes on more and more individual features. The muscular system develops. The fetus perceives sounds coming from outside, but, of course, not all, but only those that come in the form of vibrations. Fruit weight – up to 600 g.

Twenty third week

The weight of the fetus increases by another 30-50 g. The length of the fruit can reach 300 mm. The movements become more and more energetic; these movements are necessary for the proper formation of the musculoskeletal system. The accumulation of original feces in the intestines continues. The fetus already has hair on its head.

Twenty fourth week
The weight of the fruit can reach 700 g, and the length of the fruit is approximately 310 mm. The internal organs are already well developed. The systems are functioning. Therefore, a fetus born by the end of the sixth month can even (albeit rarely, and under extremely favorable conditions) exist extrauterinely. During this stage, brain tissue develops rapidly; brain cells differentiate. Those brain cells that determine consciousness reach maturity. The fetus establishes a sleep-wake cycle, and the mother knows when the fetus is “sleeping”; she does not feel its movements; “waking up”, the fetus often begins to actively move. As the fetus grows, its movements become more and more powerful; If she compared the first movements that the mother felt with the movement of bubbles or with the flapping of the wings of a butterfly (many mothers do not even pay attention to them during their first pregnancy), then later she feels real tremors from within and sometimes even shudders from them. At this stage, the fetus already feels touches on the mother’s stomach and reacts to them. And you can already “communicate” with him, which is what mothers often do. The fetus perceives sounds in the form of vibrations. Also, in the form of vibrations, the mother’s voice reaches it, and the fetus knows it. It can be assumed with a fair degree of confidence that the fetus is already able to distinguish between affectionate intonations in the mother’s voice and alarming ones. It is possible that the fetus also perceives light that barely passes through the wall of the abdomen.

Twenty-fifth and twenty-sixth weeks

The fetus is surrounded by a fairly large amount of amniotic fluid, so it has the ability to move quite actively. Reacts to changes in the position of the mother's body, to touches on the stomach, to sounds coming from outside in the form of vibrations. The fact that the fetus perceives these sounds is proven by a simple experiment: an intense sound is given and the pregnant woman’s stomach is listened through a tube; after the sound is given, the fetal heart rate increases slightly. In addition to sounds coming from outside and the mother’s voice, the fetus hears rumbling in the mother’s intestines, as well as the noise of blood moving through the mother’s large vessels. The question arises: why is the hearing acuity of a newborn child, who for the first time after birth can hear only loud sounds, knocking, so strikingly different from the hearing acuity of a fetus? The answer is simple: in a newborn child, the tympanic cavity does not yet contain air, it is filled with embryonic connective tissue, and amniotic fluid is present in the auditory tube for several days (there is no longer fluid in the external auditory canal); embryonic connective tissue puts pressure on the eardrum from the inside and prevents the latter from responding to quiet sounds; Meanwhile, in the fetus, both in the external auditory canal and in the tympanic cavity, there is practically the same environment - amniotic fluid and gelatinous embryonic connective tissue, and there is no obvious predominance of pressure on either side; and how well sounds travel in water is widely known... The skin of the fetus at this stage of development is still red, covered with a cheese-like lubricant, and unevenly covered: on the face, on the arms and thighs there is more vernix lubricant than on other parts of the body. The fetus's eyes sometimes open slightly, but mostly the eyelids seem to be glued together. There is a pupillary membrane. 1 holes are almost always blue or dark blue; Only after some time has passed after birth (several weeks) do they acquire the color that will remain for life.

Twenty seventh week

The length of the fetus already reaches 350 mm, and its weight is up to 1200 g. Since the subcutaneous fatty tissue of the fetus is still poorly developed, its skin is wrinkled, and the fetus has an “senile” appearance. The skin is red, there is a lot of cheese-like lubricant. There are vellus hairs (lanugo) over the entire surface of the body. The hair on the head reaches a length of 5 mm. The nails are short and soft. In boys, the testicles have not yet descended into the scrotum; in girls, the labia minora are not covered by the labia majora. The fetus's eyes sometimes open slightly. The cartilage of the nose and ears is soft.

Twenty eighth week

When listening (auscultating) the pregnant woman's abdomen, the fetal heartbeat can be heard clearly. The normal heart rate is 120-130 beats per minute. There is still a pupillary membrane, but it is already visible at the edge of the pupil. The ears are pressed against the head; The cartilage in the ears is still soft. The fetal nails also remain tender and soft, and they do not protrude beyond the cones of the fingers. The place where the umbilical cord joins the abdominal wall of the fetus is developed at this stage, but remains low. The fetus actively moves when it is “awake”. Sometimes he gets hiccups; Scientists believe that the cause of hiccups is in the so-called spontaneous waters. The mother may feel fetal hiccups. Periodically, the fetus continues to swallow amniotic fluid. If for some reason the birth occurs at this time, then the child, provided he is cared for very well and competently, is able to survive.

Twenty-ninth, thirty and thirty-first weeks

The process of fat accumulation under the skin of the fetus continues. Therefore, the skin becomes less and less wrinkled and more and more shiny. The skin still remains reddish, covered with germinal fuzz. The eyes continue to develop, the spectacle membrane is no longer present. Heart rate 120-140 beats per minute. The position of the fetus in the uterus is head up; What matters is the fact that the shape of the fetus at this stage of development ideally matches the shape of the uterus. However, in some cases, the fetus may turn head down already at this stage of pregnancy (usually the fetus turns over later).

Thirty second week

The fruit is actively growing; in length it can reach 450 mm, its weight is 2400-2500 g. In a normal pregnancy, the fetus in the thirty-second week of development already turns head down. If preterm labor occurs, a viable baby is born but is considered premature; The special care it requires is quite lengthy.

Thirty-third - thirty-sixth week

As a rule, by this time the fetus is already in a head-down position; This is the so-called cephalic presentation. The skin of the fetus is not as red as before. Rather, it can be called pink. The subcutaneous fat layer is already quite thick, so the skin is smoother. Fat deposits are important: firstly, it is a reliable supply of nutrition, which can be in demand in the first days after birth, and secondly, due to the heat-insulating property of fat, its deposits help retain heat, and the child’s body in conditions of extrauterine existence (which , of course, worse than the conditions of existence in utero); It is also important that fat deposits somewhat protect the fetus from mechanical influence from the outside, which is inevitable during childbirth; but if there are too many deposits (the fetus is “overfed”), labor becomes more difficult. The hair on the scalp becomes longer, while the vellus hair thins. The nails lengthen somewhat and reach the edges of the fingers, but remain soft. The cartilages of the nose and ears gradually become denser. The lungs secrete a special fatty substance - surfactant; this substance subsequently favors the functioning of the lungs. In boys, the testicles are lowered into the scrotum. The place of attachment of the umbilical cord to the abdominal wall of the fetus is already much higher. The endocrine glands (endocrine glands) begin to show activity. By the thirty-sixth week of development, the fetus already occupies a head-down position in the uterus; It should be noted here that in women with their first pregnancy, the fetus retains this position until childbirth - this is explained by the fact that the muscles of the uterus and abdomen are not yet stretched, strong, and they no longer seem to allow the fetus, which has increased in size, to change position again and again; on the contrary, in women with repeated pregnancies, the fetus may change its position in the uterus more than once. Parts of the fetal body can already be felt through the mother's abdomen. At the thirty-sixth week, the fetus reaches a length of 46 cm, and its weight is approximately 2750 g. If a child is born at this time, he screams, his lungs expand, and reflexes are expressed - sucking and grasping.

Thirty-seventh week

By this time, the fetus has significantly increased in size and is no longer able to frequently turn over in the uterus (it does not feel as comfortable as before); We have already said above that in women with their first pregnancy, the fetus is held by the unstretched muscles of the uterus and abdomen in the position it will occupy during childbirth. Since the subcutaneous fat layer is already significant, the fetal body looks plump. At this stage, the brain undergoes active development; the fetus develops the basics of consciousness. The development of the organ of vision continues; eye movements are coordinated. The placenta no longer increases in size, but continues to function actively. The growth rate of the fetus slows down somewhat.

Thirty-eighth - forty-second weeks

The fruit reaches a length of 48-52 cm, and its weight can be from 3200 to 3600 g. The weight continues to increase, although it no longer has the same rate of increase. All signs of prematurity disappear; the fetus is fully formed, all its organs and systems are able to function independently, therefore the fetus is considered mature. Boys' testicles are lowered into the scrotum; In girls, the labia minora are covered by the labia majora. The skin of the fetus is smooth due to sufficient fat deposition and has a pale pink color. Vellus hairs remain only in the shoulder girdle area. The head is covered with hair 2-3 cm long. The nails of the fetus are pink, soft, and protrude slightly beyond the fingertips. The cartilage of the nose and ears is denser and more elastic than it was before. After the fortieth week, fetal growth slows down even more; after the forty-first week, the placenta functions less and less effectively, which, of course, is one of the grounds for artificially inducing labor. A born mature child is distinguished by a loud cry and active movements - the child moves his arms and legs. During screaming, the skin turns red, the muscles of the abdomen and chest tense. Congenital reflexes are well expressed - sucking, grasping, plantar, etc.
If the fetus is born at forty-two weeks or more, it is considered post-term. It is distinguished by thick hair on its head and long nails that protrude significantly beyond the tips of its fingers. The skin of a post-term fetus is usually dry, flaky, sometimes even cracked. It is noteworthy that a post-term fetus has less vernix lubrication than a full-term fetus.
A full-term newborn baby weighs on average from 3000 to 3500 g. In the case when the weight of a newborn is in the range from 4000 to 5000 g, we are talking about a large fetus. If the weight of a newborn exceeds 5000 g, then it is customary to talk about a giant fetus.

SITUATIONAL TASKS IN EMBRYOLOGY

During the lesson, students discuss the importance of extra-embryonic organs in human embryonic development and, in particular, the yolk sac. It is known that in evolution the yolk sac performed a trophic function. In humans it contains a very small amount of yolk. Why? discuss the situation while answering the following questions

What extraembryonic organs are formed during embryogenesis in humans?

Function of the yolk sac in fish and birds

What structures (cells) form the human yolk sac?

Why does the yolk sac in humans lose its trophic function?

What functions does the yolk sac perform in humans?

During a presentation at a conference on the topic “Stages of Human Embryonic Development,” students discuss the following questions. answer them too

Fertilization (3 phases)

Type of cleavage and blastocyst formation

Types of gastrulation in humans and the formation of germ layers and axial organs

Histogenesis and organogenesis

Systemogenesis

In an experiment on an animal, the source of development of the adrenal medulla was damaged. During the discussion, questions arose. answer them too

What germ layers arise as a result of gastrulation?

During what process does this source arise?

Which germ layer gives rise to the development of this source

From what part of the ectoderm does this source develop?

What is the name of the part of the ectoderm that goes into the development of the source?

Premature placental abruption occurred, resulting in the death of the fetus. what is the reason? As you discuss the situation, answer the questions.

What extraembryonic organs develop in humans during embryogenesis?

Which organ ensures the connection between the embryo and the mother's body?

What type of placenta does a person have?

What two parts of the chorion are formed in humans?

What is the reason for premature placental abruption?

5. When discussing the topic “Sex Cells,” questions arose about the classification of eggs. answer them too

What is the name of the period in which egg formation occurs?

What is characteristic of eggs?

How are eggs classified by the amount of yolk?

How are eggs classified according to the location of the yolk?

What conditions determine the amount of yolk in the cytoplasm of the egg?

6. During the inflammatory process, the blastocyst was in the fallopian tube on the 7th day of embryogenesis. discuss the outcome of the pregnancy as you answer the following questions

Structure of the blastocyst (5-6 days)

Stages of implantation

What changes occur in the blastocyst on the 7th day?

What can happen to the blastocyst in the fallopian tube after the seventh day

What is the outcome of pregnancy

7. Students discuss in class the period of embryonic development, when cells begin to separate and specialize due to the activity of certain genes. The following questions arose. answer them too

What is this period called?

What are the 4 stages here?

At what stage do unequal blastomeres appear?

When do germ layers appear?

At what stage do the rudiments of different tissues appear?

8. At what stage of embryogenesis and how (methods) the embryo becomes multilayered. discuss this as you answer the following questions

What is this stage called and what is formed as a result of it?

What methods do lancelets and amphibians have?

How does gastrulation occur in humans?

What organs are formed in the human embryo between the two stages of gastrulation?

Time frame for the formation of all 3 germ layers in the human embryo

9. During an autopsy of a woman who died during a car accident, a vesicle-shaped embryo was found in the uterus. what stage of development and what is the gestational age? discuss the situation while answering the following questions

Stages of embryonic development and their essence

Human egg type

Site of reproductive tract of fertilization

Type of crushing in humans and localization of the process

Human blastocyst (structure, place and time of formation after fertilization)

10. The fetus was born in a “shirt”. What does it mean? what is this “shirt” made of? discuss the situation while answering questions

Gastrulation in humans

Human extraembryonic organs. Formation between gastrulation phases

Provisional organs formed after gastrulation in humans

Amnion structure

The meaning of the amnion (actions of the obstetrician if the fetus is born in a “shirt”)

ANSWERS TO SITUATIONAL PROBLEMS IN EMBRYOLOGY

In humans, during emryogenesis, extraembryonic organs are formed: amnion, yolk sac, chorion, allantois, placenta.

In fish and birds, the yolk sac performs trophic and hematopoietic functions.

In humans, the yolk sac is formed by extraembryonic endoderm and extraembryonic mesoderm (mesenchyme).

The yolk sac appears in the second week of development, and from the third week hemotrophic nutrition begins, so the yolk sac loses its trophic function.

The yolk sac is an organ that mainly performs hematopoietic function and the formation of primary germ cells in humans.

There are three phases in fertilization.

Remote interaction. Chemicals are used to prevent many sperm from entering the egg.

Contact interaction - the cytoplasm of contacting gametes combines.

Penetration of the sperm into the cytoplasm of the egg, compaction of the peripheral part of the cytoplasm of the egg and formation of the fertilization membrane.

The crushing is complete, uneven, asynchronous. Some blastomeres are large, dark, and fragment slowly. This is an embryoblast. It forms the body of the embryo and extra-embryonic organs, except for the trophoblast. The second type of blastomeres - small, light, rapidly dividing - is the trophoblast. After 50-60 hours, the crushed embryo takes the form of a dense ball - a morula. On the third day, the blastocyst begins to form, which is a hollow vesicle formed from the outside by the trophoblast and filled with liquid, with the embryoblast in the form of a knot of cells, which is attached from the inside to the trophoblast at one pole of the blastocyst.

In humans, gastrulation occurs in two phases. As a result of delamination, two layers are formed: the outer one is the epiblast (primary ectoderm) and the inner one is the hypoblast (primary endoderm). At the second stage, as a result of the formation of the primitive streak and the immigration of cell masses, the mesoderm and notochord are formed. By day 17, the human embryo has formed 3 germ layers. On days 20–21, the notochord, the neural tube (from the ectoderm), is finally formed, closing by day 25. The intestinal tube is formed.

The formation of tissue primordia occurs due to determination and commitment, differentiation, proliferation and cell death. Determination is a genetically programmed path of development of cells and tissues. At the gastrulation stage, cells are not sufficiently determined, so they are the source of the development of several tissues. Commitment is a restriction of the possible paths of cell development. Differentiation is changes in the structure of cells that are associated with their functional specialization, caused by the activity of certain genes. During the process of differentiation, specialization of tissue primordia and the formation of various types of tissues occur.

The rudiments of organs and systems are formed from tissues.

In humans, gastrulation occurs in two phases. As a result of delamination, two casts are formed: the outer one is the epiblast (primary ectoderm) and the inner one is the hypoblast (primary endoderm). At the second stage, as a result of the formation of the primitive streak and the immigration of cell masses, the mesoderm and notochord are formed.

The source arises in the process of differentiation.

Primary ectoderm.

Germinal ectoderm.

Rudiments of the sympathetic ganglia.

4.1. In human embryogenesis, extraembryonic organs are formed: amnion, yolk sac, chorion, allantois, placenta.

4.2. The connection between the embryo and the mother's body is ensured by the placenta.

4.3. The human placenta is hemochorial, discoidal, villous.

4.4. A branched chorion is distinguished, the villi of which greatly grow and branch. Smooth chorion - no villi. It is located in the region of the parietal and bursa parts of the falling shell.

4.5. At the border of the smooth and branched chorion, part of the main sheath along the edge of the placental disc grows tightly to the chorion and does not collapse, forming an endplate. If the formation of this plate is disrupted, blood flows out of the lacunae with maternal blood and the placenta exfoliates.

The process of development and maturation of eggs is called progenesis.

Eggs are characterized by the presence of yolk, which is a protein-lipid complex. This inclusion is located in the cytoplasm and is used to nourish the embryo.

Based on the amount of yolk, yolkless (alecithal) are distinguished. Small yolk (oligolecithal). Among them, primary (in the lancelet) and secondary (in placental mammals and humans) are distinguished. Polylecithal (multiyolk) (in birds).

In low-yolk eggs, the yolk granules are evenly distributed - called isolecithal. In polylecithal eggs, the yolk is often located at one pole. Such eggs are called telolecithal. Among them, a distinction is made between moderately telolecithal (mesolecithal in amphibians) and strongly telolecithal (in birds). If the yolk is in the center of the cell, then the cells are called centrolecithal.

The amount of yolk in the egg depends on the development conditions (in the external or internal environment) and the duration of development. In humans, the small amount of yolk is explained by the fact that the development of the embryo occurs in the mother’s body and nutrition is provided by the mother through the placenta.

On the fifth day, the blastocyst enters the uterus and is freely located in it. At first, the blastocyst has the appearance of a hollow vesicle, which is formed from the outside by the trophoblast and the embryoblast in the form of a nodule attached from the inside to the trophoblast. The bubble is filled with liquid. From the fifth day, the number of lysosomes in the trophoblast increases, and trophoblast outgrowths appear. The embryonic nodule turns into the embryonic shield. Preparations are underway for the first phase of gastrulation.

There are two stages in implantation: adhesion (sticking) and invasion (penetration). On the resulting trophoblast villi, two layers are formed: the inner cytotrophoblast and the outer symplastotrophoblast, which produces proteolytic enzymes that melt the uterine mucosa. An implantation pit appears in it, into which the blastocyst penetrates.

On the 7th day, process cells - extra-embryonic mesoderm - are evicted from the embryonic shield. It participates in the formation of the amnion (together with the extra-embryonic ectoderm), the yolk sac (together with the extra-embryonic endoderm) and the chorion (together with the trophoblast).

The blastocyst, ready for implantation, can immerse itself in the mucous membrane of the fallopian tube.

Pipe rupture with intra-abdominal bleeding; surgery (tubectomy)

The stage is called germ layer differentiation.

There are 4 stages of differentiation:

Ootypic differentiation - at the zygote stage is represented by presumptive rudiments - sections of the fertilized egg.

Blastomer differentiation at the blastula stage.

Rudimentary differentiation at the early gastrula stage.

Histogenetic differentiation at the late gastrula stage.

At the stage of blastomere differentiation, unequal blastomeres appear (roof, bottom blastomeres...).

Germ layers arise during the early gastrulation stage.

The rudiments of various tissues appear at the stage of histogenetic differentiation. The rudiments of organs and systems begin to form from tissues.

8.1. The embryo becomes multilayered at the gastrulation stage.

8.2. In the lancelet, gastrulation proceeds by invagination (invagination), and in amphibians it occurs mainly by epiboly (fouling) plus partial invagination.

8.3. In humans, gastrulation occurs in two ways: delamination (splitting - two layers are formed: the outer layer - the epiblast (primary ectoderm) and the inner hypoblast (primary endoderm)). The second method is immigration (eviction, movement of cellular material).

8.4. Between the two stages of gastrulation, extraembryonic organs are formed: the amniotic and vitelline vesicles, the chorion - organs that provide conditions for the development of the embryo.

8.5. By day 17, the embryo has formed all 3 germ layers - ectoderm, endoderm and mesoderm.

Fertilization is the formation of a single-celled organism - a zygote. As a result of fragmentation, the embryo becomes multicellular. Gastrulation is the formation of a multilayer embryo. Histogenesis, organogenesis and systemogenesis - tissues appear in the embryo, from the combination of which organs and systems are formed. The human body is formed.

Secondary isolecithal egg

In the fallopian tubes

Complete, uneven, asynchronous. It begins in the fallopian tube and ends in the uterus.

Blastocyst is a germinal vesicle. At the early blastocyst stage (3–4 days), formed in the fallopian tube, the embryo enters the uterine cavity. There, the free blastocyst stage (days 5–6) is followed by implantation (days 6–7), lasting 40 hours. In a blastocyst there is a trophoblast (outer cell mass) on the outside, and a cavity with liquid on the inside. At one pole of the vesicle there is an embryoblast (inner cell mass) attached to the trophoblast. Gestation period is the end of the first week from fertilization (about 6 days).

Gastrulation in humans occurs in two phases: phase 1 – delamination on the 7th day with the formation of epi- and hypoblast; Phase 2 on day 14 (immigration). In the embryo, three germ layers are formed and the main organs (axial) are formed.

The amnion, yolk sac, and chorion appear between the two phases of gastrulation

After the second stage, the allantois is formed and the placenta begins to form

Composition of the amnion: extraembryonic ectoderm and mesoderm (mesenchyme)

The amnion is a water membrane - a hollow organ filled with fluid produced by its epithelium. The fetus develops in it and makes movements. The amnion protects the fetus from drying out and has the effects necessary for the formation of the digestive and respiratory organs. The fetus swallows amniotic fluid and secretes urine into it. The obstetrician opens the amnion for normal labor (if it has not opened itself).

Endosperm is the nutritious tissue of the seed of a monocot and dicotyledonous plant 3) The main function of seeds is plant reproduction

4) The pistil consists of an ovary and a style and stigma

5) The pistil is the organ where the ovule and egg are formed

6) the main part of the flower is a bright perianth that attracts pollinators

7) a seedling of any plant consists of two parts, a root and a shoot

8) The growth cone is an actively working growth part of the shoot

9) internodes are areas of the stem between the leaves

10) leaf organ of photosynthesis, gas exchange and evaporation

11) stomata are respiratory cells in the skin of the leaf

12) Flower is the organ of sexual reproduction from which the fruit develops after pollination and fertilization

13) all plant organs consist of cells and tissues

14) modification of organs is due to the acquisition of new functions in connection with the life of the plant in changing environmental conditions

15) cambium cells carry out the growth of the stem in length

16) rhizome is a modified shoot and tuber is a modified stem

17) plants form main lateral and adventitious root systems 18) Pollination is the transfer of pollen from the anthers of the stamen to the stigma 19) The pistil of a flower is pollinated by insects and the wind

20) the main parts of the vegetative shoot are the stem, leaves, buds; the main parts of the generative shoot are the flower, fruit, seeds.

1. Inside the seed, under the skin, is the embryo of a new plant.
2.Endosperm is an important nutritious tissue of the seed of a monocotyledonous and dicotyledonous plant.
3.The main function of seeds is to spread plants.
4. The pistil consists of an ovary, a style and a stigma.

5. The pistil is the organ where the ovule with the egg is formed.

6.The main part of the flower is a bright perianth that attracts pollinators.

7. The seedling of any plant consists of two parts - the root and the shoot.

8.The growth cone is the actively working growth part of the shoot.

9. Internodes - areas of the stem between the leaves.

10. Leaf is an organ of photosynthesis, gas exchange, evaporation.

11. Stomata are respiratory cells in the skin of a leaf.

12. A flower is an organ of sexual reproduction, from which the fruit develops after pollination and fertilization.

13. All plant organs consist of cells and tissues.

14.Modification of organs is due to the acquisition of new functions in connection with the life of the plant in changing environmental conditions.

15. Cambium cells carry out the growth of the stem in length.

16. The rhizome is a modified shoot, and the tuber is a modified stem.

17.Plants form main, lateral and adventitious root systems.

18. Pollination is the transfer of pollen from the anthers of the stamen to the stigma of the pistil.

19.The pistil of a flower is pollinated by insects and the wind.

20. The main parts of the vegetative shoot are the stem, leaves, buds; the main parts of the generative shoot are the flower, fruit, seeds.

Please help, thank you in advance!

1. Inside the seed, under the skin, is the embryo of a new plant.
2.Endosperm is the nutritious tissue of the seed of a monocotyledonous and dicotyledonous plant.
3.The main function of seeds is plant propagation.
4. The pistil consists of an ovary, a style and a stigma.
5. The pistil is the organ where the ovule with the egg is formed.
6.The main part of the flower is a bright perianth that attracts pollinators.
7. The seedling of any plant consists of two parts - the root and the shoot.
8.The growth cone is the actively working growth part of the shoot.
9.Internodes are the areas of the stem between the leaves.
10. Leaf is the organ of photosynthesis, gas exchange and evaporation.
11. Stomata are respiratory cells in the skin of a leaf.
12.A flower is an organ of sexual reproduction, from which the fruit develops after pollination and fertilization.
13. All plant organs consist of cells and tissues.
14.Modification of organs is due to the acquisition of new functions in connection with the life of the plant in changing environmental conditions.
15. Cambium cells carry out the growth of the stem in length.
16. The rhizome is a modified shoot, and the tuber is a modified stem.
17.Plants form main, lateral and adventitious root systems.

2. Cosmic role of green plants. (table)
Results of vital processes of green plants (4 points)
The meaning of these processes (4 points)

The study of the development of the human body from the formation of a single-celled zygote, or fertilized egg, until the birth of a child. Embryonic (intrauterine) human development lasts approximately 265–270 days. During this time, more than 200 million cells are formed from the original one cell, and the size of the embryo increases from microscopic to half a meter.
In general, the development of a human embryo can be divided into three stages. The first is the period from fertilization of the egg to the end of the second week of intrauterine life, when developing embryo(the embryo) implants into the wall of the uterus and begins to receive nutrition from the mother. The second stage lasts from the third to the end of the eighth week. During this time, all the main organs are formed and the embryo acquires the features of a human body. At the end of the second stage of development, it is already called a fruit. The length of the third stage, sometimes called fetal (from the Latin fetus - fetus), is from the third month to birth. At this final stage, the specialization of organ systems is completed and the fetus gradually acquires the ability to exist independently.

GENIT CELLS AND FERTILIZATION

A person has a mature sex cell(gamete) is a sperm in a man, an ovum (egg) in a woman. Before gametes fuse to form a zygote, these sex cells must form, mature, and then meet.

Human germ cells are similar in structure to the gametes of most animals. Fundamental difference The difference between gametes and other cells of the body, called somatic cells, is that the gamete contains only half the number of chromosomes of a somatic cell. There are 23 of them in human germ cells. During the process of fertilization, each germ cell brings its 23 chromosomes into the zygote, and thus the zygote has 46 chromosomes, i.e., a double set of them, as is inherent in all human somatic cells. See also CELL.

While similar in their main structural characteristics to somatic cells, the sperm and egg are at the same time highly specialized for their role in reproduction. A sperm is a small and very motile cell (see SPERM). The egg, on the contrary, is immobile and much larger (almost 100,000 times) than the sperm. Most of its volume is made up of cytoplasm, which contains reserves of nutrients necessary for the embryo during the initial period of development (see EGG).

For fertilization, the egg and sperm must reach maturity. Moreover, the egg must be fertilized within 12 hours after leaving the ovary, otherwise it dies. Human sperm lives longer, about a day. Moving quickly with the help of its whip-shaped tail, the sperm reaches the duct connected to the uterus - the fallopian tube, where the egg enters from the ovary. This usually takes less than an hour after copulation. Fertilization is believed to occur in the upper third of the fallopian tube.

Despite the fact that the ejaculate normally contains millions of sperm, only one penetrates the egg, activating a chain of processes leading to the development of the embryo. Due to the fact that the entire sperm penetrates the egg, the man brings to the offspring, in addition to nuclear material, a certain amount of cytoplasmic material, including the centrosome, a small structure necessary for the cell division of the zygote. The sperm also determines the sex of the offspring. The culmination of fertilization is considered to be the moment of fusion of the sperm nucleus with the nucleus of the egg.

CRUSHING AND IMPLANTATION

After fertilization, the zygote gradually descends through the fallopian tube into the uterine cavity. During this period, over a period of about three days, the zygote goes through a stage of cell division known as cleavage. During fragmentation, the number of cells increases, but their total volume does not change, since each daughter cell is smaller than the original one. The first cleavage occurs approximately 30 hours after fertilization and produces two completely identical daughter cells. The second cleavage occurs 10 hours after the first and leads to the formation of a four-cell stage. Approximately 50–60 hours after fertilization, the so-called stage is reached. morula - a ball of 16 or more cells.

As cleavage continues, the outer cells of the morula divide faster than the inner cells, resulting in the outer cell layer (trophoblast) being separated from the inner cluster of cells (the so-called inner cell mass), maintaining connection with them in only one place. A cavity, the blastocoel, is formed between the layers, which is gradually filled with liquid. At this stage, which occurs three to four days after fertilization, cleavage ends and the embryo is called a blastocyst, or blastula. During the first days of development, the embryo receives nutrition and oxygen from the secretions of the fallopian tube.

Approximately five to six days after fertilization, when the blastula is already in the uterus, the trophoblast forms finger-like villi, which, moving vigorously, begin to penetrate the uterine tissue. At the same time, apparently, the blastula stimulates the production of enzymes that promote partial digestion of the uterine lining (endometrium). Around day 9–10, the embryo implants (grows) into the wall of the uterus and is completely surrounded by its cells; With implantation of the embryo, the menstrual cycle stops.

In addition to its role in implantation, the trophoblast is also involved in the formation of the chorion, the primary membrane surrounding the embryo. In turn, the chorion contributes to the formation of the placenta, a membrane with a spongy structure, through which the embryo subsequently receives nutrition and removes metabolic products.

EMBRYONAL GERM LAYERS

The embryo develops from the inner cell mass of the blastula. As fluid pressure increases within the blastocoel, the cells of the inner cell mass become compact and form the germinal shield, or blastoderm. The embryonic shield is divided into two layers. One of them becomes the source of the three primary germ layers: ectoderm, endoderm and mesoderm. The process of separation of first two and then the third germ layer (the so-called gastrulation) marks the transformation of the blastula into the gastrula.

The germ layers initially differ only in location: the ectoderm is the outermost layer, the endoderm is the inner layer, and the mesoderm is intermediate. The formation of the three germ layers is completed approximately a week after fertilization.

Gradually, step by step, each germ layer gives rise to certain tissues and organs. Thus, the ectoderm forms the outer layer of the skin and its derivatives (appendages) - hair, nails, skin glands, lining oral cavity, nose and anus, – as well as the entire nervous system and sensory organ receptors, such as the retina. From the endoderm are formed: lungs; the lining (mucosa) of the entire digestive tract except the mouth and anus; some organs and glands adjacent to this tract, such as the liver, pancreas, thymus, thyroid and parathyroid glands; lining of the bladder and urethra. Mesoderm is the source of the circulatory system, excretory, reproductive, hematopoietic and immune systems, as well as muscle tissue, all types of supporting trophic tissue (skeletal, cartilaginous, loose connective tissue, etc.) and the inner layers of the skin (dermis). Fully developed organs usually consist of several types of tissues and are therefore related by their origin to different germ layers. For this reason, it is possible to trace the participation of one or another germ layer only in the process of tissue formation.

EXTRAGEMONY MEMBRANES

The development of the embryo is accompanied by the formation of several membranes that surround it and are rejected at birth. The outermost of them is the already mentioned chorion, a derivative of trophoblast. It is connected to the embryo by a body stalk of connective tissue derived from the mesoderm. Over time, the stalk lengthens and forms the umbilical cord (umbilical cord), connecting the embryo to the placenta.

The placenta develops as a specialized outgrowth of the membranes. The chorionic villi pierce the endothelium of the blood vessels of the uterine mucosa and plunge into the blood lacunae filled with the mother’s blood. Thus, the blood of the fetus is separated from the blood of the mother only by the thin outer membrane of the chorion and the walls of the capillaries of the embryo itself, i.e., direct mixing of the blood of the mother and the fetus does not occur. Nutrients, oxygen and metabolic products diffuse through the placenta. At birth, the placenta is discarded as an afterbirth and its functions are transferred to the digestive system, lungs and kidneys.

Within the chorion, the embryo is contained in a sac called the amnion, which is formed from the embryonic ectoderm and mesoderm. The amniotic sac is filled with fluid that moisturizes the embryo, protects it from shocks and keeps it in a state close to weightlessness.

Another additional shell is the allantois, a derivative of endoderm and mesoderm. This is the storage place for excretory products; it connects with the chorion in the bodily stalk and promotes respiration of the embryo.

The embryo has another temporary structure - the so-called. yolk sac. Over a period of time, the yolk sac supplies the embryo with nutrients by diffusion from the maternal tissues; Later, progenitor (stem) blood cells are formed here. The yolk sac is the primary site of hematopoiesis in the embryo; subsequently this function passes first to the liver and then to the bone marrow.

EMBRYO DEVELOPMENT

During the formation of extraembryonic membranes, the organs and systems of the embryo continue to develop. At certain moments, one part of the cells of the germ layers begins to divide faster than the other, groups of cells migrate, and cell layers change their spatial configuration and location in the embryo. During certain periods, the growth of some types of cells is very active and they increase in size, while others grow slowly or stop growing altogether.

The nervous system is the first to develop after implantation. During the second week of development, the ectodermal cells of the posterior side of the germinal shield rapidly increase in number, causing the formation of a bulge above the shield - the primitive streak. Then a groove is formed on it, in the front of which a small pit appears. In front of this fossa, the cells quickly divide and form the head process, the precursor of the so-called. dorsal string, or chord. As the notochord elongates, it forms an axis in the embryo, providing the basis for a symmetrical structure human body. Above the notochord is the neural plate, from which the central nervous system is formed. Around the 18th day, the mesoderm along the edges of the notochord begins to form dorsal segments (somites), paired formations from which the deep layers of skin, skeletal muscles and vertebrae develop.

After three weeks of development, the average length of the embryo is only slightly more than 2 mm from crown to tail. Nevertheless, the rudiments of the notochord and nervous system, as well as eyes and ears, are already present. There is already an S-shaped heart, pulsating and pumping blood.

After the fourth week, the length of the embryo is approximately 5 mm, the body is C-shaped. The heart, which forms the largest bulge on the inside of the body's curve, begins to subdivide into chambers. Three primary areas of the brain (brain vesicles), as well as the visual, auditory and olfactory nerves are formed. The digestive system is formed, including the stomach, liver, pancreas and intestines. The structuring of the spinal cord begins, and small paired limb rudiments can be seen.

A four-week human embryo already has gill arches that resemble the gill arches of a fish embryo. They soon disappear, but their temporary appearance is one example of the similarity of the structure of the human embryo with other organisms (see also EMBRYOLOGY).

At five weeks of age, the embryo has a tail and the developing arms and legs resemble stumps. Muscles and ossification centers begin to develop. The head is the largest part: the brain is already represented by five brain vesicles (cavities with fluid); there are also bulging eyes with lenses and pigmented retinas.

In the period from the fifth to the eighth week, the actual embryonic period of intrauterine development ends. During this time, the embryo grows from 5 mm to approximately 30 mm and begins to resemble a person. His appearance changes as follows: 1) the curvature of the back decreases, the tail becomes less noticeable, partly due to reduction, partly because it is hidden by the developing buttocks; 2) the head straightens, the outer parts of the eyes, ears and nose appear on the developing face; 3) the arms are different from the legs, you can already see the fingers and toes; 4) the umbilical cord is fully defined, the area of ​​its attachment on the abdomen of the embryo becomes smaller; 5) in the abdominal area, the liver grows greatly, becoming as convex as the heart, and both of these organs form a lumpy profile of the middle part of the body until the eighth week; at the same time, the intestines become noticeable in the abdominal cavity, which makes the stomach more rounded; 6) the neck becomes more recognizable mainly due to the fact that the heart moves lower, as well as due to the disappearance of the gill arches; 7) external genitalia appear, although they have not yet fully acquired their final appearance.

By the end of the eighth week, almost all internal organs are well formed, and the nerves and muscles are so developed that the embryo can produce spontaneous movements. From this time until birth, the main changes in the fetus are associated with growth and further specialization.

COMPLETION OF FETAL DEVELOPMENT

During the last seven months of development, the weight of the fetus increases from 1 g to approximately 3.5 kg, and the length increases from 30 mm to approximately 51 cm. The size of the baby at the time of birth can vary significantly depending on heredity, nutrition and health.

During fetal development, not only its size and weight, but also body proportions change greatly. For example, in a two-month-old fetus, the head is almost half the length of the body. In the remaining months it continues to grow, but more slowly, so that by the time of birth it is only a quarter of the body's length. The neck and limbs become longer, while the legs grow faster than the arms. Other external changes are associated with the development of the external genitalia, the growth of body hair and nails; the skin becomes smoother due to the deposition of subcutaneous fat.

One of the most significant internal changes is associated with the replacement of cartilage by bone cells during the formation of a mature skeleton. The processes of many nerve cells are covered with myelin (a protein-lipid complex). The process of myelination, together with the formation of connections between nerves and muscles, leads to increased mobility of the fetus in the uterus. These movements are well felt by the mother after about the fourth month. After the sixth month, the fetus rotates in the uterus so that its head is down and rests on the cervix.

By the seventh month, the fetus is completely covered with vernix, a whitish fatty mass that disappears after birth. It is more difficult for a child born prematurely to survive during this period. As a rule, the closer the birth is to normal, the greater the chance of survival for the baby, since in the last weeks of pregnancy the fetus receives temporary protection from certain diseases due to antibodies coming from the mother's blood. Although childbirth marks the end of the intrauterine period, human biological development continues during childhood and adolescence.

DAMAGING EFFECTS ON THE FET

Birth defects can result from a variety of causes, such as disease, genetic abnormalities, and numerous harmful substances that affect the fetus and the mother. Children with birth defects may be disabled for life due to physical or mental disabilities. Growing knowledge about the vulnerability of the fetus, especially in the first three months when its organs are forming, has now led to increased attention to the antenatal period.

Diseases. One of the most common causes of birth defects is viral disease rubella. If a mother contracts rubella in the first three months of pregnancy, it can lead to irreparable abnormalities in the development of the fetus. Young children are sometimes given the rubella vaccine to reduce the chance that pregnant women who come into contact with them will get the disease. See also RUBELLA.

Sexually transmitted diseases are also potentially dangerous. Syphilis can be transmitted from mother to fetus, resulting in miscarriages and stillbirth. Detected syphilis must be immediately treated with antibiotics, which is important for the health of the mother and her unborn child.

Fetal erythroblastosis can cause stillbirth or severe anemia in the newborn with the development of mental retardation. The disease occurs in cases of Rh incompatibility between the blood of the mother and the fetus (usually with a repeat pregnancy with an Rh-positive fetus). See also BLOOD.

Another hereditary disease is cystic fibrosis, the cause of which is a genetically determined metabolic disorder, affecting primarily the function of all exocrine glands (mucous, sweat, salivary, pancreas and others): they begin to produce extremely viscous mucus, which can clog both the ducts themselves glands, preventing them from secreting secretions, and small bronchi; the latter leads to severe damage to the bronchopulmonary system with the eventual development of respiratory failure. In some patients, the activity of the digestive system is primarily disrupted. The disease is detected soon after birth and sometimes causes intestinal obstruction in the newborn on the first day of life. Some manifestations of this disease are amenable to drug therapy. Galactosemia is also a hereditary disease, caused by the lack of an enzyme necessary for the metabolism of galactose (a product of the digestion of milk sugar) and leading to the formation of cataracts and damage to the brain and liver. Until recently, galactosemia was a common cause of infant mortality, but methods have now been developed early diagnosis and treatment through special diet. Down syndrome (see DOWN SYNDROME), as a rule, is caused by the presence of an extra chromosome in cells. A person with this condition is usually short in stature, with slightly slanted eyes and reduced mental abilities. The likelihood of a child having Down syndrome increases with maternal age. Phenylketonuria is a disease caused by the lack of an enzyme necessary to metabolize a certain amino acid. It can also be a cause of mental retardation (see PHENYLKETONURIA).

Some birth defects can be partially or completely corrected through surgery. These include birthmarks, club feet, heart defects, extra or fused fingers and toes, abnormalities in the structure of the external genitalia and genitourinary system, spina bifida, cleft lip and cleft palate. Defects also include pyloric stenosis, i.e. narrowing of the transition from the stomach to the small intestine, absence of the anus and hydrocephalus - a condition in which excess fluid accumulates in the skull, leading to an increase in the size and deformation of the head and mental retardation (see also CONGENITAL VICES).

Medicines and drugs. Evidence has accumulated—many from tragic experience—that some medicines may cause abnormalities in fetal development. The best known of these is the sedative thalidomide, which has caused underdeveloped limbs in many children whose mothers took the drug during pregnancy. Currently, most doctors recognize that drug treatment in pregnant women should be kept to a minimum, especially in the first three months when organ formation occurs. The use of any medications by a pregnant woman in the form of tablets and capsules, as well as hormones and even inhalation aerosols, is permissible only under the strict supervision of a gynecologist.

Drinking large amounts of alcohol by a pregnant woman increases the risk of the baby developing many conditions, collectively called fetal alcohol syndrome, which include growth retardation, mental retardation, cardiovascular abnormalities, a small head (microcephaly), and poor muscle tone.

Observations have shown that cocaine use by pregnant women leads to serious problems in the fetus. Other drugs such as marijuana, hashish and mescaline are also potentially dangerous. A link has been found between pregnant women's use of the hallucinogenic drug LSD and the incidence of spontaneous miscarriages. Experimental evidence suggests that LSD can cause abnormalities in chromosome structure, indicating the possibility of genetic damage in an unborn child (see LSD).

Smoking by expectant mothers also has an adverse effect on the fetus. Studies have shown that, in proportion to the number of cigarettes smoked, cases of premature birth and fetal underdevelopment increase. Smoking may also increase the frequency of miscarriages, stillbirths, and infant mortality immediately after childbirth.

Radiation. Doctors and scientists are increasingly pointing out the danger associated with the continuous increase in the number of sources of radiation, which can cause damage to the genetic apparatus of cells. During the early stages of pregnancy, women should not be unnecessarily exposed to X-rays and other forms of radiation. More broadly, strict control of medical, industrial and military sources of radiation is vital to preserving the genetic health of future generations. See also REPRODUCTION; HUMAN REPRODUCTION; EMBRYOLOGISTS

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