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The development of the child's heart. When a fetal heartbeat appears, possible disorders

Every part of the body depends on the ability of the heart to pump blood every second, every minute, every day, starting from the moment a person was born in a woman's womb. At the same time, the cardiovascular system is the first and largest system that begins to function in the embryo.

The fetal cardiovascular system begins to form the very first, since the embryo needs independent blood circulation. This allows other organs to develop fully. The process of development and formation of the embryonic cardiovascular system takes approximately 5 weeks, starting at the third and ending by the eighth.

Today they say that the life of a child does not begin from the moment of his birth, but from the moment of conception. There is strong evidence for this, since on the 22nd day after the fertilization of the egg, the first pulsation of the future heart is noted, and on the 26th day in the fetus, which is only 3 mm in size, the blood begins to circulate on its own.

For thousands of years, the heart has been considered one of the most important organs in the body. Aristotle even believed that there were other organs to "cool" him, including the brain and lungs (which are now known to perform their own vital functions). While it may not be as Aristotle once thought, the heart does indeed fulfill the role that is essential for survival.

Video: 1-9 weeks of pregnancy

Heart tube and embryonic vessels

The development of the heart begins in the third week with the formation of two endothelial tubes called angioblast chordae.

Two heart tubes develop from these formations, which merge into one by the end of the third week due to lateral embryonic bending.

By the fourth week, the developing heart receives blood from three pairs of veins:

Yolk veins.
umbilical veins.
Common cardinal veins.

The yolk veins carry oxygenated blood from the yolk sac and enter the sinus venosus. The umbilical veins carry oxygenated blood from the chorion, the original placenta. The common cardinal veins carry oxygenated blood from the rest of the embryo.

Because the primary liver develops in close association with the transverse septum, the hepatic ducts join and surround the epithelial membranes to form the primary hepatic sinusoids. These primary sinusoids connect with the vitelline veins, which pass through the transverse septum and enter the sinus venosus, also called the venous end of the heart. The left vitelline veins regress and the right vitelline veins form the hepatic veins, with the network of vitelline veins around the duodenum forming the portal vein.

As the liver develops, the umbilical veins lose contact with the heart and regress. The right umbilical vein and the cranial part of the left umbilical vein degenerate at the seventh week of pregnancy, leaving only the caudal part of the left umbilical vein. Its caudal part carries oxygenated blood to the embryo from the placenta. The umbilical vein is connected to the inferior vena cava (IVC) by a ductus venosus that develops in the liver. This bypass directs most of the blood directly to the heart from the placenta, bypassing the liver.

Umbilical vein - ventral view

The outflow of blood from the embryo occurs mainly through the cardinal veins, while the anterior cardinal vein collects blood from the cranial part of the embryo, and the posterior cardinal vein drains the caudal part. These two connections form the common cardinal vein, which enters the sinus venosus.

By the eighth week, the anterior cardinal veins are connected by a vessel that runs obliquely between them. This formation allows blood to flow from the left anterior cardinal vein to the right. Once the caudal portion of the left anterior cardinal vein degenerates, this anastomosis becomes the left brachiocephalic vein. The right anterior cardinal vein and the right common cardinal vein eventually become the superior vena cava (SVC), and the posterior cardinal veins are part of the common iliac veins and the azygos vein (v. azygos).

As soon as the subcardinal and supracardinal veins form, they begin to complement, and soon replace, the posterior cardinal veins. The subcardinal veins appear first and eventually form part of the left renal vein, adrenal vein, gonadal vein, and inferior vena cava (IVC). Above the kidneys, the anastomoses join the supracardinal veins to form the unpaired and semi-unpaired veins. Beneath the kidneys, the right supracardinal vein enters the IVC, while the left supracardinal vein degenerates.

During the fourth and fifth weeks of development, the pharyngeal arches form. They are supplied by the pharyngeal arch arteries, which connect the aortic sac to the two dorsal parts of the aorta. The dorsal aorta runs along the embryo, eventually merging at the tail to form the lower thoracic and abdominal aorta. The remaining right dorsal aorta degenerates, and the rest of the left dorsal aorta becomes the original aorta.

In the dorsal aorta, intersegmental arteries are isolated, which supply blood to the somites (primary segments) and their derivatives. These intersegmental arteries become:

vertebral arteries in the neck;
intercostal arteries in the chest;
lumbar arteries and common iliac arteries in the abdominal cavity;
lateral sacral arteries in the sacral region. The caudal dorsal aorta passes into the medial sacral artery, while any other intersegmental arteries regress.

The yolk sac, allantois, and chorion are supplied by unpaired branches of the dorsal aorta. The yolk sac is supplied by biliary arteries, and once a certain part of it forms the primary intestine, this area is also supplied by biliary arteries.

The bile arteries lead to the development of the celiac arteries, the superior mesenteric artery supplies blood to the midgut; and the inferior mesenteric artery delivers blood to the hindgut.

Two umbilical arteries located in the umbilical cord carry oxygen-deprived blood in the direction of the embryo → placenta. The proximal portion of these arteries becomes the internal iliac and superior vesical arteries, while the distal portion regresses to become the medial umbilical ligaments.

Development of the layers of the heart

As the two endothelial tubes fuse, the primary myocardium begins to form from the tribal mesoderm around the pericardial cavity. This original layer of the heart later becomes its middle layer, the myocardium. The endothelial tube forms the endocardium, the inner layer of the heart. The epicardium, the outer layer, is derived from mesothelial cells from the outer layer of the sinus venosus.

Histology of cardiac tissue

Growth and folding of the heart tube

When the cranial part of the embryonic fold is formed, the heart tube lengthens. As this happens, the heart tube develops alternating contractions and expansions. As a result, the bulb of the heart (bulbus cordis), ventricle, atrium and venous sinus are formed. The bulb of the heart contains several components, including the arterial trunk (truncus arteriosus), arterial cone (conus arteriosus) and cardiac cone.

The arterial trunk is located cranial to the aortic sac with which it is connected, and the arteries of the pharyngeal arch depart from it. It is through them that blood leaves the heart, while returning to the venous sinus of the heart through the umbilical, yolk and common cardinal veins.

The bulb of the heart and the ventricles grow faster than the other developing parts of the heart, causing the organ to bend and fold on its own to form the onion-ventricular circuit. As the kink develops, the atria and sinus venosus move so that they are dorsal to the truncus arteriosus, the bulbus cordis, and the ventricles. During this time, the venous sinus occupies a lateral position, its left and right horns are determined.

The heart is initially attached by the mesentery to the dorsal wall of the pericardial cavity, called the dorsal mesocardium, but as the heart grows, it begins to fill the pericardial cavity and the central portion of the dorsal mesocardium degenerates. The loss of part of this mesentery allows the formation of a connection between the left and right sides of the pericardial cavity due to the formation of a transverse pericardial sinus.

The movement of blood through the primitive heart

The venous sinus receives blood from the common cardinal veins, umbilical veins and yolk veins.

The common cardinal veins carry blood from the embryo.
The umbilical veins carry blood away from the placenta.
The yolk veins carry blood from the umbilical bladder.

After entering the sinus venosus, blood flows through the sinus valve into the primary atrium. It then flows out of the atrium into the primary ventricle through the atrioventricular (AV) canal. When the primary ventricle contracts, it pumps blood into the umbilical cord and through the truncus arteriosus into the aortic sac. From there, blood flows into the pharyngeal arch arteries and then into the dorsal aorta. Then the blood returns to the embryo, placenta and umbilical bladder.

Video: Heart Development

Separation of the developing heart

In the middle of the fourth week of fetal development, the atrioventricular canal, primary atrium, and ventricle begin to separate. This process is completed by the end of the eighth week. It begins with the formation of endocardial cushions, specialized extracellular matrix tissue associated with myocardial tissue. At the end of the fourth week, these cushions appear on the ventral and dorsal walls of the AV canal and begin to grow towards each other. They eventually fuse, dividing the AV canal into left and right components, partially separating the atrium and ventricle and acting as AV valves.

The original atrium is divided into the right and left atria by two septa, the septum primum and secundum (primum and secundum). The primary septum appears first as a thin membrane growing from the roof of the original atrium towards the endocardial cushions, leaving an opening between its edge and the endocardial cushion. This formation is called the foramen primum, and it allows blood to continue to flow from the right atrium to the left. It gradually contracts and eventually closes as the primum septum elongates and fuses with the endocardial cushions to form the original AV septum.

Before the foramen primum is completely closed, apoptosis of cells in the middle of the septum forms perforations. These perforations form a new second opening, an internal compartment, which allows oxygenated blood to flow from the right atrium to the left, even after the primal opening has been closed.

The muscular septum, septum secundum, grows along with the septum primum, to the right of it. It grows downward from the ventro-cranial wall of the atrium during the fifth and sixth weeks of development, gradually overlapping the inner sheath in the septum primum. By blocking the internal opening without merging with the primum, an incomplete barrier between the atria is formed. At this stage of development, the opening between the atria is called the foramen ovale, and it allows oxygenated blood to continue to flow from the right atrium to the left.

Due to the presence of a kind of flap-like valve, the flow of blood in the opposite direction, from the left to the right atrium, is prevented: the thin septum primum is pressed against the more rigid and inflexible septum septum, blocking the return of blood through the foramen ovale. Although the cranial part of the primum septum slowly regresses, some parts of it remain attached to the endocardial cushions. These residual portions of the primary septum form an oval-shaped valve.

After the birth of a child, the pressure in the left atrium increases significantly, becoming much higher than the pressure in the right atrium. This leads to the fact that the primum septum is pressed against the septum septum, and the valves of the primum opening merge with the septum in a second, functionally closing the foramen ovale. When this happens, the foramen ovale becomes the fossa ovale and the two septa form a complete barrier between the atria.

Venous sinus, its derivatives and development of the right atrium

The sinoatrial opening, that is, the opening of the venous sinus in the primary atrium, is originally located on the back wall of the original atrium. This situation changes at the end of the fourth week, when the right sinus horn becomes larger than the left one. This uneven growth moves the sinus opening to the right, so it will subsequently be in the right atrium. As the right sinus horn continues to grow, blood from the head and neck region of the embryo flows into it through the SVC, and blood from the placenta and the rest of the embryo flows into it through the IVC. Subsequently, the venous sinus integrates into the wall of the right atrium in the form of a smooth area, the sinus venarum (sinus venarum). The rest of the inner surface of the right atrium and the ear has a thicker, trabecular appearance. These parts of the adult atrium originate from the primary atrium.

The transition from the smooth to the rough inner surface of the right atrium is internally defined by an atrial ridge called the crista terminalis, which originates from the cranial part of the right sinoatrial valve, and externally by a groove called the sulcus terminalis. The caudal portion of the right sinoatrial valve forms the IVC and coronary sinus valves.

The left sinus horn develops into the coronary sinus; and the left sinoatrial valve eventually fuses with the septum secundum, becoming part of the atrial septum.

Interatrial septum - side view

Primary pulmonary vein, its derivatives and development of the left atrium

Most of the inner wall of the left atrium is smooth and is derived from the primary pulmonary vein, which develops from the dorsal atrial wall to the left of the septum primum. As the left atrium grows, the primary pulmonary vein, as well as its major branches, integrates into the atrial wall. This results in four pulmonary veins entering the left atrium. The left atrium has the same origin as the right atrium - the primary atrium. Thus, its inner surface has a trabecular structure.

Development of the ventricles

The primary ventricle begins to divide into two ventricles with the growth of the median crest, a muscular interventricular (VH) septum with an upper free margin that arises from the base of the primary ventricle near the apex of the heart. The expansion of the developing ventricles on either side of this septum is responsible for the initial increase in the height of the septum. Further growth of the latter occurs due to ventricular myocytes located on both sides of the heart.

Between the upper free edge of this septum and the endocardial cushions there is an opening called the IV hole. Through it, blood continues to flow from the right ventricle to the left until complete closure at the end of the seventh week, when the left and right bulbar crests merge with the endocardial cushion, forming the membrane part of the IV septum. In the fifth week, the bulbar crests are formed by the division of neural crest mesenchymal cells in the walls of the bulbus (heart bulb).

The membranous part of the IV septum occurs when the tissue on the right side of the endocardial cushion extends to the muscular part of the IV septum, eventually merging with the aortopulmonary septum and the muscular IV septum. As soon as the IV opening closes and the membranous part of the IV septum is formed, the aorta becomes the only outflow of blood from the left ventricle, and the pulmonary trunk becomes the only outflow of blood from the right ventricle.

As the ventricles develop, cavitation leads to the formation of muscle bundles. While some of these persist as columns of muscles on the inner surface of the ventricles (trabeculae carneae), others form the papillary muscles and chordae tendinae (heart strings) that connect the papillary muscles to the AV valves.

Posterior papillary muscle - left side image

Bulb of the heart and truncus arteriosus

Bulbar crests are formed from mesenchymal cells of the neural crest. The migration of these cells is induced by bone morphogenic protein (BMP) and other signaling pathways. These bulbar and stem ridges are spirally arranged at a 180 degree angle. Their confluence forms a spiral aortopulmonary septum, which divides the bulb of the heart and the arterial trunk into the aorta and pulmonary trunk.

As the heart continues to develop, the bulbus cordis integrates into the ventricular walls into their smooth portion. In the right ventricle, the bulb of the heart becomes an arterial cone, which contributes to the development of the pulmonary trunk. In the left ventricle, the bulb of the heart becomes the vestibule of the aorta, part of the left ventricle just below the aortic valve.

Formation of heart valves

The aortic and pulmonary semilunar valves develop from three pads of subendocardial tissue present around the aortic orifice and pulmonary trunk. They turn into three tubercles.

Tricuspid and mitral AV valves are formed from proliferative tissue surrounding the AV channels. The structure of the tricuspid valve includes three tubercles, and the mitral (that is, bicuspid) valve has two. In the future, the valves have three and two flaps, respectively.

Anterior protrusion of the mitral valve - cranial view

Conducting system formation

Initially, the primary atrium functions as a pacemaker for the developing heart; but the venous sinus soon assumes this role. At the fifth week, the sinoatrial node (SA) develops in the right atrium near the entrance of the SVC. After the sinus venosus is integrated into the heart, cells from its left wall are found near the opening of the coronary sinus at the base of the atrial septum. With the addition of some cells from the AV region, the AV node and bundle form just above the endocardial cushions. The pathways originating from the AV bundle extend from the atrium to the ventricle and divide into left and right branches of the bundle, which are found throughout the ventricular myocardium. Ultimately, the SA node, AV node, and AV bundle receive nerve innervation from outside the heart. At this stage, the development of the primary conducting system is completed.

Key points:

The cardiovascular system begins to develop the very first, as this allows the entire body to develop fully.
The future heart begins to pulsate already on the 22nd day after the fertilization of the egg.
On the 26th day, independent circulation of blood through the primitive circulatory system is noted.
The development of the heart in the fetus goes through a series of complex and strictly regular stages. Violation of one of them can lead to the death of the embryo or congenital malformations.
Every sexually active woman needs to be extremely careful and take a responsible approach to a possible conception, because at three weeks, when there are no signs of pregnancy, the heart is already beginning to form in the fetus. If at this time he is exposed to negative factors of influence, then he may develop malformations.

Video: Embryology of the development of the heart, malformations

From the moment when the fertilization of the egg occurs until the moment of birth, nine months pass. There are several critical periods in the development of the embryo:

This is his attachment to the wall of the uterus;
When the heart of the embryo begins to beat, the first contractions appear; the formation of the main organs and systems.

Seven days after a fertilized egg has appeared in the woman's body, the embryo attaches to the mucous wall of the uterus. For its survival, this is a vital and necessary process. First, the embryo is attached to the uterine mucosa, and then, as it were, is introduced into it. Attachment and implementation take about 48 hours;
The embryo at the “age” of four weeks is quite a crumb, only about 1 mm in size. However, it is during this period that cells begin to divide inside it. They form three germ layers. The middle layer later "turns" into the circulatory system, muscles, internal organs;
At a period of five obstetric weeks, a hollow tube is formed in the embryo, which plays the role of the primary circulatory system. Later it will become the heart;
Five obstetric weeks of pregnancy is about 25 days of embryo development. It is during this period that the tube makes the first, so far independent of the nervous system, contraction.
Already on the sixth pulsation will become audible and noticeable on ultrasound machines.
It is not yet possible to say that this is a beating heart, it is still single-chamber, and although it pumps blood through the growing body of a child;
In the seventh week, it will become two-chamber, due to the appearance of a muscular septum. During this period, the heart rate is very high, about 150 beats per minute;
The structure of a small heart becomes more complicated by the 10-11th week of pregnancy. Two ventricles, two atria are formed, separating valves and vessels are determined. Also, already from this period, an open oval window is noticeable on ultrasound - it connects the aorta and the pulmonary artery. This is how oxygen from the mother's blood reaches the baby. The foramen ovale should close after birth.

It is possible to determine whether everything is normal with the child's heart, whether it has formed and functions normally, already from a period of 22 weeks.

An embryo is called an embryo in the first two months of its intrauterine development, and it is correct to call it a fetus after the third month of development.

We have already said above that the first shocks can be determined from the 25th day of fertilization. After 30 days, independent blood circulation is already taking place inside the growing organism.

To hear or see beats and contractions, obstetricians use the following methods and tools:

Ultrasound study. For a period of 5-6 weeks transvaginally, for a period of more than 6-7 transabdominally, when the heart of the fetus begins to beat;
Stethoscope - effective after 18-20 weeks.

To determine the state of blood flow and listen to the frequency of contractions, dopplerometry is prescribed. The operation of the device is to measure the speed of blood flow.

Doppler also helps to hear the heartbeat, determine the state of the main organ, and assess the blood flow in the umbilical cord. Doppler is prescribed for a period not earlier than 22-24 weeks of pregnancy, and at 30-34.

At a period of 22-23 weeks of pregnancy, CTG or cardiotocography is also prescribed. The procedure allows you to fix contractions for a certain period. This is an easy way to track an increase or decrease in heart rate depending on the activity of the fetus. The study shows the relationship between the nervous system and the heartbeat.

After the heartbeat appears, more precisely, immediately after it makes the first beats, the process is not yet controlled by the nervous system. The system itself is formed on the 12th day from the moment of fertilization. Up to 23 days, it is a tube. But by the 28th day, the system is almost completely formed.

For a period of 20-25 days, the first nerve fibers grow to the heart. The heart rate changes as the child grows.

The first, uncontrolled shocks occur at a period of five obstetric weeks. Nervous-controlled heartbeats occur from 32 weeks.

In the last trimester, therefore, the connection between the nervous system and the beating of the heart is fully visible. In a healthy child, the heart beats rhythmically, at regular intervals. Arrhythmia is an indicator of either hypoxia (when there is not enough oxygen, the heart rate rises), or the presence of malformations or pregnancy. Poorly distinguishable contractions can serve as indirect signs of polyhydramnios or oligohydramnios.

Modern research methods help to determine at an early stage, firstly, whether the child is alive, secondly, whether everything is in order with him, thirdly, whether there are any anomalies in the development and course of pregnancy that may threaten the life of the child or mother. Therefore, it is important to undergo planned ultrasound, CTG and Doppler as prescribed by the doctor.

So, a new life was born. Whether you wanted it or not, whether the fruit of your love is desirable or not, it doesn't matter. The egg, formed in the ovary, passed through the tubes, settled in the uterine mucosa, accepted and merged with the sperm. This is already a fertilized egg that will grow and eventually become your child.

This life, still only one cell, carries all the information contained in your genes, i.e. the smallest protein molecules, and in your partner's genes. We will return to this. But now, the cells have merged, and in the first two weeks after conception, the processes of formation of cell systems begin, which then turn into tissues and organs.

As the amazing poet Dmitry Kedrin once wrote:

“Still nausea and spots are not even in sight.
And your belt is just as narrow, even if you look in the mirror.
But you are elusive, according to secret female signs
Frightened guessed what you have inside ... "

In the beginning, new life takes the form of a disk. Sometimes such a small protein disk can be seen in the yolk of a broken chicken egg. It is called an embryo, and in the early days it is just a collection of wise cells that know exactly what they need to do. With each subsequent hour, the cells become more and more. They connect and fold into certain shapes, forming first two tubes, then, merging, one. This tube folds and descends from the primary disc to form a loop called the primary cardiac loop. The loop quickly lengthens, significantly outstripping the growth and increase in the number of cells surrounding it, lies to the right, in the form of such a ring as a mooring rope ring, which is thrown onto the bollard when a boat or vessel is moored. This loop normally lies only on the right, otherwise the future heart will lie not on the left, but on the right of the sternum. And on the 22nd day after conception, the first contraction occurs in the thickened lower part of the loop. The heart began to beat. You can try to remember what happened then with the future mother. What state was she in? What happened to her? And, if you, like the vast majority of married and single couples, did not pay attention to this, I can guarantee that you will not remember. You will say: “So what?”, - and you will be right. As a rule, nothing. But still, think about it. The first days may not solve anything. But the next will decide a lot.

The cardiovascular system of the fetus is the first of all its systems to form, because the fetus needs its own blood circulation for the full development of its other organs. The development and formation of the cardiovascular system begins in the third week and, in general, ends by the eighth week of the embryo's life, i.e. takes place over five weeks.

We will briefly describe these stages, but now we ask ourselves the question: “What is 4-5 weeks of pregnancy today?”. A woman is not yet sure if she is pregnant, especially if she does not expect this event too much. She does not change her lifestyle, habits, sometimes harmful. She can work in heavy and hazardous production or do hard physical work at home. She can carry a viral infection in the form of influenza on her feet. Usually a couple does not think yet, tries not to think about the future, but it - this is the future - is not only living, but also beating, shrinking, growing. But wait to execute yourself - there may be other reasons. About them - later. In the meantime, remember: today in the world they believe that the life of a child begins not from the moment of his birth, but from the moment of conception.

So, on the 22nd day, the future heart begins to pulsate, and on the 26th day in the body of the fetus, whose length is 3 millimeters, independent blood circulation begins. Thus, by the end of the fourth week, the fetus has a beating heart and circulation. So far, this is one stream, one curved tube, in the bend of which lies the "motor" - the heart. But every minute processes take place in it that lead to the final formation. It is very important to understand that these processes take place simultaneously in three-dimensional space and in order for “everything to fit together correctly and accurately”, their complete synchronization is needed. Moreover, if this did not happen, i.e. at some point, something did not connect where it was needed, the growth and development of the heart does not stop. Everything goes on. After all, when some musician suddenly plays a false note in the orchestra, the orchestra will still play the symphony. But the false sound will fly away and be forgotten, and few people will pay attention to it, but the forming heart will remember it. And now the growing partition has nowhere to attach, or the valve has nothing to hold on to. This is how birth defects are formed. In order for the heart to become four-, and not two-chambered (as in the third week), it is necessary that its septa grow (interatrial and interventricular), so that the common arterial trunk is divided into an aorta and a pulmonary artery, so that inside the common ventricle it is divided into right and left so that the aorta connects with the left ventricle so that the heart valves are fully formed. All this happens between the 4th and 8th week of pregnancy, (at this time the length of the fetus reaches only 3.5-4 cm). By the end of the second month of pregnancy, everything is already formed in the "inch" (3.5 cm) embryo. Obviously, the earlier in this process there was a violation of normal development, the more the heart becomes deformed, i.e. the more severe his congenital defect. The later this happened, the smaller the structural change will be and the easier it will be to correct the defect in the future.

Quoted from the book G. E. Falkovsky, S. M. Krupyanko. Child's heart. A book for parents about congenital heart defects

“The heart is the source of our feelings, hobbies, love. It allows you to taste the joy of life.
Yes, this amazing organ is the heart!
(from the animated series about the structure of the human body for children "Once upon a time there was a life").

The heart is the most important and complex physical organ of a person.
This is due, on the one hand, to its main functions for the entire human body, on the other hand, it provides a wide variety of congenital malformations.

From the school curriculum in biology, we remember that the human heart has 4 chambers (2 atria and 2 ventricles), which acts as a pumping function. The right half (right atrium and right ventricle) of the heart collects the oxygen-poor used blood and sends it to the lungs. The left half (left atrium and left ventricle) receives oxygenated blood from the lungs and sends it to human tissues and organs. Thus, thanks to the heart, the “clockwork” of supplying the organs with food and returning the used blood with oxygen from the organs to the lungs is maintained. The formation of the heart already begins from early pregnancy and at the stages of embryogenesis performs its main function of fetal circulation. Cardiac embryogenesis is the gradual construction of cardiac structures from 2 to 6 weeks of gestation. It is this period that is especially sensitive in terms of risk factors for the development of congenital malformations of the baby's cardiovascular system, which we will analyze in our next article.

The anlage of the heart appears in the embryo at the end of the 2nd week of development from simple 2 heart tubes, which, merging together, form a common heart tube and blood flows in one continuous stream.
At the end 3rd - beginning of the 4th week the embryo undergoes uneven growth of the heart tube and this leads to a change and complication of the shape. A sigmoid or S-shaped heart is formed, in which a venous sinus is distinguished, followed by a venous section (primary ventricle), an arterial section (primary atrium) and then a common arterial trunk. The heart at this stage is single-chamber and during this period it begins to contract.
In the further stages of development, the venous and arterial parts of the heart grow, and a deep constriction occurs between them. Both knees of the arterial section gradually grow together. This is how the two-chambered heart of the embryo is formed ( 4th week of development).
At this stage there is only a large circle of blood circulation; the small circle develops later in connection with the development of the lungs. A further stage of development is the formation of an interatrial septum (the stage of a three-chambered heart or 5-6 weeks of development ).

On 6th week of development the embryo, the ventricular chamber is divided by means of the interventricular septum, and valves are simultaneously formed and the common arterial trunk is divided into the aorta and pulmonary artery (four-chamber heart stage).

On within 6-7 weeks , in the already practically “ready” heart, the construction of the interventricular septum, which separates the right and left ventricles of the heart, ends.
The blood circulation of the fetus has its own characteristics, unlike adults, since the respiratory and digestive systems practically do not function in utero.
So, how does a baby manage to do without breath, cookies and delicious buns?

All nutrients and oxygen are supplied with the mother's blood through auxiliary devices, which include the placenta, umbilical cord and fetal communications (ductus venosus, foramen ovale and ductus arteriosus).
Fetal communications are the heart structures of the fetus, with the help of which the blood mixes (unlike adults) and most of it enters the left sections, since the lungs do not perform gas exchange. Let's analyze in detail how this happens.

The umbilical vein from the placenta collects rich oxygenated (arterial) blood with nutrients and directs it to the liver, where it divides into 2 branches: the portal vein and the venous duct. The portal vein supplies blood to the abdominal organs (liver, intestines, etc.).
venous duct - 1- fetal communication or vessel connecting the umbilical vein to the fetal heart. Mixing of blood occurs at the level of the inferior vena cava, which in turn collects poor used blood (venous) from the lower part of the body.
Then the mixed blood is sent to the right atrium, where venous blood from the upper pudendal vein comes from the upper part of the body.
The blood flow from the right atrium to the right ventricle is divided into 2 paths associated with the lack of breathing of the baby.
First way begins with the flow of blood from the right atrium into the right ventricle and then into the lungs with the help of the pulmonary trunk, which divides its branches into the right and left lungs.
Since the alveoli do not produce gas exchange and are filled with fluid (a systemic spasm of all arterioles occurs), where 1/3 of the blood returns through the pulmonary veins to the left atrium.
Second way: the remaining 2/3 of the blood is forced to flow through such fetal communications as the oval window and arterial duct.

oval window - 2 - fetal communication is an opening with a valve between the atria. The mixed blood that enters the left atrium flows into the left ventricle and then into the aorta, where it is carried to all organs of the fetus. From the abdominal aorta, 2 umbilical arteries depart, giving blood back to the placenta, carbon dioxide and waste products of the fetus. It is important to note that in the placenta, the blood of the mother and fetus does not mix in any way, the mother's blood cells give off oxygen and receive "waste" from the baby's blood cells.

ductus arteriosus - 3 - fetal communication or a vessel connecting the pulmonary trunk (LS) to the aorta, where blood is discharged into the aorta.

Given such a complex and multi-stage mechanism for the development of the cardiovascular system, various kinds of effects on the body of a pregnant woman in the embryonic and early fetal periods can lead to a wide range of congenital anomalies of this system. And we will talk about this in the next article.

Heart originally has a pair bookmark, it appears in a person at that stage of development, when the embryo is still prostrate in the plane. At this time, the heart is a paired large vessel. In animals with a lower content of yolk in the egg (in amphibians and in lower fish), the heart from the very beginning is laid in the form of a single endothelial tube.

However, in cases where germ develops from a flat germinal shield, the laying of the heart due to the large amount of yolk in the egg (in higher fish, reptiles and, finally, in mammals) should be double, its fusion into a single heart tube occurs a second time.

basis human heart is the area of the so-called cardiogenic plate, which is already observed in the embryos protruding in the plane under the cranial, head end of the body of the embryo in the thickened mesoderm of the splanchnopleura. First, several irregularly shaped slits appear dorsal to this plate, which eventually merge into a continuous single cavity of the future pericardial (pericardial) cavity.

It is generally the first part of the pawned embryonic body cavity. The area of the cardiogenic plate and anlages of the pericardial cavity, located on both sides of the body, after the isolation of the cranial end of the embryo from the environment, moves, as already described above, to its ventral side, then being located ventral to the head intestine.

At the same time, the bookmark of the heart rotates in such a way that its sections, which lie first cranially, are located caudally, and the anlage of the pericardial cavity moves ventral to the anlage of the heart.

First laying of the heart tube is a collection of thickened mesenchymal cells lying in the region of the cardiogenic plate. These cells on both sides of the body are distributed in two longitudinally passing strips, in which gaps subsequently appear; thus, two endothelial tubes extending longitudinally and laterally appear, located on both sides of the head intestine in two folds of mesenchyme, protruding into the anlage of the pericardial cavity.

As convergence of both anlages between themselves, both tubes gradually merge with each other along the midline, forming a single heart tube, and the fusion first occurs in a more cranially located area. At the same time, their mesenchymal membrane also merges into a single, so-called myoepicardial tube, which is the rudiment for the heart muscles and epicardium. At first, the caudal sections of the heart tube are not connected yet.

They are double and present a bookmark of both future atria. In the process of fusion, both anlages of the pericardial cavity merge into a single pericardial cavity. The primary heart tube in this cavity is attached to its posterior wall by a double fold of mesenchyme, which is called the cardiac mesentery - mesocardium. Finally, the caudal sections of the heart tube also unite, due to which a single, generally still straight heart tube arises.

This stage of development is formed during fourth embryonic week. From the very beginning there is no anlage of the ventral cardiac mesentery, and the dorsal cardiac mesentery subsequently disappears almost completely.