Human Anatomy - A Course of Lectures - Kostylenko Yu.P. 2015

General Anatomy of the Cardiovascular System

Lecture Plan:

6.1. Significance of the Circulatory system for humans.

6.2. General Anatomy of arterial vessels.

6.3. Structure OF THE microcirculatory Blood bed.

6.4. General anatomy of venous vessels.

6.5. Characteristics of human circulatory loops.

6.6. Certain features of The Vascular System of the HEAD.

6.7. General Anatomy of the heart.

6.8. Features of Fetal Circulation.

6.1 Significance of the circulatory system for humans

As is well-known, The basis of life is METABOLISM. The continuous delivery of nutrients and oxygen necessary for vital activity to living Tissues, and the equally uninterrupted removal of Metabolic waste products and carbon dioxide, are carried out in the body via a mobile liquid medium.

In The Human Body, as in all vertebrates, There are two relatively closed vascular systems through which fluid circulates: the circulatory system, which is well-developed, and The Lymphatic system, which is less pronounced and not present in all Organs and tissues.

The human circulatory system provides a constant, rhythmic movement of the liquid medium—blood—throughout the entire body and can be conditionally divided into two parts: the central part, The Heart, and the peripheral part, the Blood Vessels.

Among the vessels, a distinction is made between Arteries, through which blood moves from the heart to the organs and tissues; Veins, through which blood flows from the organs and tissues to the heart; and the intermediate link between arteries and veins—the microvascular bed.

6.2 General anatomy of arterial vessels

The largest arterial vessel, into which blood enters directly from the heart under significant pressure, is the aorta. A large number of arteries branch off from the aorta toward organs and tissues, subsequently dividing into smaller vascular trunks. There are three MAIN TYPES OF arterial branching: dichotomous, when a vascular trunk divides into two subsequent ones; stem (or trunk-based), when side branches depart from the main vessel, usually at an acute angle open toward the periphery; and dispersed, in which a single vessel breaks up into several or numerous small arteries.

In a living person, arteries appear as trunks of a regular cylindrical shape. In a corpse, their shape changes somewhat: the cylinder appears compressed from the sides. This is due to the fact that after clinical death, arterial vessels continue to contract and push blood into the capillaries for some time, As a result of which they appear empty. The lumens of the arteries become partially filled with gases of decomposition. In this regard, an incorrect name for arteries has taken ROOT (from *aer* — air, *tereo* — I keep), because ancient anatomists believed that air moved through the arteries.

As arteries branch out toward the periphery, their caliber becomes smaller and smaller. Consequently, arterial vessels are generally divided into large (8 mm in diameter and larger), medium (2–8 mm), and small (2 mm and smaller). Each arterial vessel usually maintains a uniform caliber and a straight direction until it gives off side branches.

The wall of arteries, like that of hollow Internal Organs, consists of three tunics: the inner tunic (*tunica intima*), the middle tunic (*tunica media*), and the outer tunic (*tunica adventicia*). The inner tunic is lined on the inside by a single layer of squamous epithelium—endothelium—beneath which, in the Connective Tissue foundation, lies a relatively weakly expressed internal elastic membrane.

The middle tunic is the thickest and consists predominantly of circular and longitudinal Muscle layers, interspersed with elastic fibers.

The third, outer tunic is represented by Connective tissue with a small amount of muscle and elastic fibers. In addition to the aforementioned structures, numerous blood vessels that nourish the arterial wall, as well as nerves, run through the walls of the arteries.

Depending on the content of elastic and muscle fibers in the vessel wall, elastic, muscular, and mixed-type arteries are distinguished. The former receive the blood ejected during cardiac systole, expand, and recoil without significant participation of muscular elements. Conversely, in muscular-type arteries (predominantly of small and medium caliber), the contraction of smooth myocytes in the muscular tunic generates a secondary pulse wave capable of propelling blood through the extensive capillary bed. These arteries are sometimes referred to as the "peripheral heart."

All arteries connect with one another more or less extensively through their branches. Such connections between adjacent vascular trunks are called anastomotic vessels (anastomoses).

Blood vessels connecting two or more distant vascular trunks are called collateral vessels. Both types of vascular connection are of vital importance in cases where impaired Blood flow through one trunk is either fully or partially compensated by blood inflow from other vessels. At the same time, the body contains some arteries that lack these connections.

The distribution of arteries in the human body follows certain regular patterns:

1) Arteries are located along the course of the neural tube and nerves. Thus, the main arterial trunk—the aorta—runs parallel to the Spinal Cord, while in the limbs, arteries course near major nerves, forming neurovascular bundles.

2) Arteries are divided into parietal and visceral (supplying the body walls and internal organs, respectively); Examples include the parietal and Visceral Branches of the descending aorta.

3) Each limb receives a single main trunk: the Subclavian Artery for the upper limb and the external iliac artery for the lower limb.

4) The Arteries of the trunk retain a segmental arrangement, as seen in the intercostal and lumbar arteries.

5) The majority of arteries are distributed according to THE PRINCIPLE OF bilateral Symmetry.

6) Arteries run adjacent to veins and Lymphatic vessels, forming a common vascular complex.

7) The course of arteries corresponds to the Skeletal structure. For instance, the aorta runs along THE Vertebral Column, and the intercostal arteries run along the Ribs. Proximal limb segments containing a single bone (humerus, Femur) contain a single main vessel, whereas intermediate segments with two bones contain two main arteries.

8) Arteries follow the shortest path from the parent trunk to the organ, following an approximately straight line.

9) Arteries are located on the flexion surfaces of the body, since the vascular tube stretches and collapses during extension.

10) Around the JOINTS OF THE Limbs, arteries form vascular networks.

After passing through the ramifications of the Arterial System, blood reaches the microcirculatory bed. Microcirculation refers to the directed movement of fluids in the tissues surrounding Blood and Lymphatic microvessels.

6.3 Structure of the Blood Microcirculatory Bed

Blood microvessels constitute the first component of the microcirculation system. Its second component comprises the pathways for substance transport within tissues, while the third component is formed by lymphatic microvessels. All three Components of the microcirculation system are functionally interconnected and interact with one another. Microcirculation ensures tissue metabolism and maintains the constancy of the internal environment necessary for the body. Impairments in microcirculation underlie many pathological processes, primarily Vascular Diseases.

The blood microcirculatory bed consists of several links, each possessing distinct anatomical and functional features.

Arterioles represent the initial link of the microcirculatory bed, with a diameter of 15–30 µm. Similar to arteries, the wall of an arteriole consists of three tunics—intima, media, and adventitia—however, the smooth muscle Cells of the media in these microvessels are arranged in a single layer. Due to the presence of smooth myocytes, the arteriolar wall can contract, narrowing their lumen.

Precapillaries, or precapillary arterioles, have a diameter of 8–20 µm and typically branch off from arterioles at a right angle. At their points of origin and along their course, smooth muscle cells form precapillary sphincters, which regulate blood flow into the capillaries. Through their contractile activity, arterioles and precapillaries ensure the distribution of blood among individual areas of the capillary bed.

Blood capillaries are the primary structural unit of the microcirculatory system. They play a leading role in the Metabolic exchange between blood and tissues. The blood flow velocity in capillaries is 0.8 mm/s. Capillaries are distributed almost universally, being absent only in the epithelium of the Skin and mucous membranes, tooth dentin and enamel, heart valve endocardium, and the cornea and internal transparent media of the Eyeball.

Capillaries are thin-walled endothelial tubes devoid of contractile elements. They can be straight, corkscrew-shaped, spiral, hairpin-looped, or wound into coils. The average length of a capillary is about 750 µm. Capillaries lack side branches; therefore, instead of branching, they divide into new capillaries and interconnect to form capillary networks. The shape, spatial orientation, and density of capillary networks are organ-specific and closely related to the Structural and functional Features of the organs. Capillary diameters range from 2–4 to 30–40 µm.

Capillaries with a narrow lumen and thick wall are found in the Lungs, Brain, and visceral smooth muscle. Glands possess capillaries with a larger luminal diameter, while the widest lumens are observed in the capillaries of the Liver, Spleen, Bone Marrow, and certain Endocrine glands. Capillaries feature arterial and venous segments, although morphological distinctions between them are detectable only at the electron-microscopic level.

Depending on their functional state, the following types of capillaries are distinguished:

8. Functioning, open capillaries, through which formed blood elements move.

9. Plasma, semi-open capillaries, containing only Blood Plasma.

10. Closed, reserve capillaries.

The ratio between the number of open and closed capillaries is determined by the functional state of the organ. If the level of metabolic processes remains reduced for a prolonged period, the number of closed capillaries increases, and some of them undergo regression. This occurs, for instance, in Muscles during a significant decrease in physical activity in bedridden patients, during limb immobilization due to fractures, etc. Conversely, under increased functional load on a particular organ, new capillary formation (angiogenesis) may occur within it.

Postcapillaries, or postcapillary venules, are formed by the convergence of several capillaries. They possess thin, distensible walls devoid of muscle cells. The diameter of postcapillaries ranges from 8 to 30 µm. Postcapillaries empty into venules, which together constitute the initial components of the Venous system.

Venules have a diameter of 30-100 µm; their walls are thicker than those of postcapillaries, and smooth muscle cells begin to appear within them. Venules interconnect via anastomoses to form complex networks.

Arteriovenous anastomoses play a crucial role in regulating blood flow within the microcirculatory bed. They serve as direct connections between arterioles and venules.

Assuming that the diameter of an anastomosis is 10 times greater than that of a blood capillary, according to Poiseuille's law, blood flow through the anastomosis per unit time exceeds that of a capillary by 10⁴, i.e., 10,000 times. Thus, in terms of blood propulsion, a single arteriovenous anastomosis is equivalent to 10,000 capillaries (Fig. 6.1).

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Fig. 6.1 Diagram of the microcirculatory bed structure:

1 — arteriole;

2 — venule;

3 — capillaries;

4 — arteriovenous anastomoses.

The structure of microvascular complexes is closely related to organ architecture. The latter determines the Spatial Organization of the entire microcirculatory bed. In laminar structures and membranes, vascular networks have a two-dimensional arrangement; in hollow organs, they are arranged in layers, forming multi-tiered structures; whereas in parenchymal organs, they exhibit a three-dimensional organization.

6.4 General Anatomy of Venous Vessels

The volume of the venous bed exceeds that of the arterial bed. This is due to the fact that the flow velocity of arterial blood is significantly higher than that of venous blood.

Like arterial walls, the walls of veins consist of three tunics: internal, middle, and external. However, venous walls are thinner, and their muscular and elastic elements are poorly developed. Externally, a vein appears as a thin-walled, flaccid vessel which, unlike an artery, does not always maintain a cylindrical shape and is easily compressible.

Due to sluggish venous blood flow under certain conditions (such as prolonged standing), prerequisites for venous stasis may arise, potentially leading to VARICOSE VEINS OF the lower extremities.

Adaptive structures that prevent venous stasis are largely the venous Valves present in the lumen of many veins, especially those in the lower limbs. These valves are formed by folds (duplicates) of the tunica intima in the shape of pockets, which allow centripetal flow of venous blood while preventing its backflow.

The VEINS OF THE limbs are divided into superficial (subcutaneous) and deep veins, which are extensively interconnected by anastomoses. Deep veins typically accompany each corresponding artery in pairs and are termed venae comitantes.

The veins of the human body can be divided into four systems: 1) the cardiac wall venous system, 2) the SUPERIOR VENA CAVA system, 3) the INFERIOR VENA CAVA system, and 4) the hepatic portal system.

The superior and inferior vena cava systems are not entirely isolated from each other; rather, they are connected by anastomoses known as cava-caval anastomoses.

The most important cava-caval anastomoses include:

1) anastomoses between the superficial veins of the anterior and lateral walls of the chest and abdomen;

2) anastomoses between the lumbar, azygos, and hemiazygos veins;

3) vertebral venous plexuses (the most prominent cava-caval anastomosis).

The portal vein collects blood from all unpaired abdominal organs, with the exception of the liver. The necessity of a portal system lies in the fact that venous blood draining from The Stomach, Small Intestine, and Large Intestine carries dissolved toxic compounds alongside nutrients; these toxins are detoxified in the liver (by stellate macrophages), and only thereafter does the purified blood enter the general circulation.

The portal vein forms portosystemic (portacaval) anastomoses with both vena cava systems. The most significant portacaval anastomoses are:

1) The portacaval anastomosis in the region connecting the veins of the abdominal part of the Esophagus with the veins of the cardiac part of the stomach. The esophageal veins are tributaries of the azygos and hemiazygos veins, which drain into the superior vena cava, whereas the gastric veins drain into the tributaries of the portal vein.

2) Portosystemic anastomosis in the walls of the rectum. The rectal venous plexus located here has two outflow pathways: the superior rectal veins carry blood into the inferior mesenteric vein, which empties into the portal vein, whereas the middle and inferior rectal veins are tributaries of the internal iliac vein, which belongs to the inferior vena cava system.

3) Portosystemic anastomoses on the anterior abdominal wall in the umbilical region are formed by the interconnection of tributaries of the superior and inferior epigastric veins with the paraumbilical veins, which extend from the umbilical ring within the round ligament of the liver alongside the obliterated umbilical vein and empty into the left branch of the portal vein.

4) Portosystemic anastomoses of the retroperitoneal space. This group of anastomoses is formed by connections between the tributaries of the splenic and mesenteric veins (colic veins) on the one hand, and the paired tributaries of the inferior vena cava (renal, testicular/ovarian, and lumbar veins) and the roots of the azygos and hemiazygos veins on the other hand.

Portosystemic anastomoses do not function under normal conditions; they open when BLOOD FLOW IN the portal venous system is impaired (portal Hypertension syndrome). This pathology can be caused by liver cirrhosis—where intrahepatic Branches of the portal vein narrow due to connective tissue proliferation—tumor compression, congenital narrowing of the hepatic veins (Budd-Chiari syndrome), and similar conditions.

When portosystemic anastomoses become active, venous blood from the stomach and intestines containing toxic substances bypasses The Liver and enters the superior or inferior vena cava system, resulting in systemic poisoning, or intoxication. Simultaneously, the veins of the esophagus and rectum dilate, and a tangle of distended, tortuous veins forms beneath the abdominal skin, known as the "caput medusae." Rupture of these dilated esophageal veins can cause massive Hemorrhage, which is frequently the cause of death in patients with liver cirrhosis.

6.5 CHARACTERISTICS OF THE Human Circulatory Loops

The pathway of Blood Circulation in all mammals (including humans) is divided into two main loops: the systemic circulation, which delivers nutrients and oxygen to all organs and Tissues of the body, and the Pulmonary Circulation, which serves to oxygenate the blood in the lungs.

Some authors also distinguish a separate cardiac circuit, which provides Blood supply to the heart, and the placental circuit (functioning during Embryogenesis).

The systemic circulation originates in the left ventricle of the heart. Through the aorta and its numerous branches, blood enters the capillary bed, where nutrients and oxygen are delivered to the tissues across the thin capillary walls. From the capillaries, blood is collected by veins into the superior and inferior vena cavae, which empty into the right atrium.

The pulmonary circulation begins in the right ventricle. Through the pulmonary trunk and its branches, blood flows into the capillary bed of the lungs. Across the walls of the pulmonary capillaries and alveoli, Carbon dioxide is eliminated from the blood and oxygen is absorbed. From the pulmonary capillary bed, blood is collected into two right and two left Pulmonary veins, which empty into the left atrium (Fig. 6.2).

6.6 Certain Features of the Vascular System of the Head

The topography and structure of the Blood vessels of the head have certain peculiarities, primarily concerning the venous bed. A characteristic feature of the veins of the head is that most of them run independently of the arteries. In the cranial region, intracranial and extracranial veins are distinguished.

The former include cerebral veins, meningeal veins, and Dural Venous Sinuses. Sinuses are endothelial-lined venous channels situated within the thickness of the dura mater, primarily at the sites where its processes attach to the cranial bones. In cross-section, the lumen of the sinuses has a triangular contour. Their walls, formed by tightly stretched sheets of the dura mater, do not collapse when cut and remain gaping upon injury. The rigidity of the venous sinus walls ensures unimpeded blood outflow during various fluctuations in intracranial pressure, which is essential for the uninterrupted activity of the brain—explaining why such structures are found exclusively in the Skull.

Fig. 6.2 Scheme of blood circulation:

1 — pulmonary (small) circulation loop;

2 — systemic (large) circulation loop.

The following sinuses are distinguished: 1) superior sagittal sinus; 2) inferior sagittal sinus; 3) straight sinus; 4) transverse sinus; 5) sigmoid sinus; 6) cavernous sinus; 7) intercavernous sinus; 8) superior petrosal sinus; 9) inferior petrosal sinus. Blood from all venous sinuses collects into the sigmoid sinus and then drains into the Internal jugular vein.

Cerebral veins are divided into superficial and deep groups. Superficial veins run in the pia mater of the brain and empty into the dural sinuses. Deep veins carry blood into the internal cerebral veins, which lie within the tela choroidea of the Third ventricle; the right and left internal veins unite to form the great cerebral vein, which empties into the beginning of the straight sinus.

In addition to cerebral veins, labyrinthine veins and the superior ophthalmic vein empty into the sinuses. Meningeal veins collect blood from the dura mater; they exit the cranial cavity and drain partly into the retromandibular vein and partly into the internal jugular vein. The latter is a direct continuation of the sigmoid sinus and drains the bulk of the blood from the cranial cavity.

Intracranial veins communicate with extracranial veins via diploic veins and emissary veins. Diploic veins lie within the channels of the spongy substance of the cranial vault bones, between the outer and inner tables, and communicate extensively with the venous sinuses and emissary veins.

Emissary veins pass through the foramina of the cranial bones, connecting the dural sinuses and diploic veins with the veins of the soft tissues of the Head and Neck. Blood can flow through them in both directions, which is why infectious processes can spread via these vessels into the cranial cavity (Figs. 6.3, 6.4).

The parietal emissary vein is located in the parietal foramen and connects the superior sagittal sinus with the superficial temporal vein. The mastoid emissary vein also passes through the mastoid foramen, connecting the sigmoid sinus with the occipital vein. The condylar emissary vein is located in the condylar canal, linking the sigmoid sinus with the external vertebral venous plexus. The occipital emissary vein passes through the occipital protuberance area, connecting the confluence of sinuses with the occipital vein. Furthermore, intracranial veins communicate with extracranial veins via the venous plexuses of the hypoglossal canal, foramen ovale, and carotid canal.

Facial veins are divided into superficial and deep. Blood from the external PARTS OF THE face is drained primarily by the facial vein. The initial segment of this vein, known as the angular vein, anastomoses with the superior ophthalmic vein, which enters the cranial cavity and empties into the cavernous sinus. This anastomosis is one of the pathways through which infectious agents (e.g., from a furuncle of the upper lip or External Nose) can enter the cranial cavity, leading to life-threatening complications.

Fig. 6.3 Schematic diagram of the dural venous sinus of the brain:

1 — diploic vein; 2 — emissary vein; 3 — sinus; 4 — cerebral vein.

Fig. 6.4 Diploic veins.

The deep facial veins primarily drain blood into the pterygoid venous plexus, located around the pterygoid muscles. From this plexus, blood is carried via the short maxillary vein into the retromandibular vein, which connects with the facial vein and empties into the internal jugular vein. The pterygoid venous plexus anastomoses both with intracranial veins, through the venous plexus of the foramen ovale, and with the superficial facial veins.

The deep and superficial veins are connected by the inferior ophthalmic vein, which near the margin of the Orbit anastomoses with tributaries of the facial vein; the inferior ophthalmic vein may drain into the maxillary vein or the pterygoid plexus, and in some cases, it enters the cranial cavity and empties into the cavernous sinus. The most important branch connecting the superficial and deep veins is the deep facial vein (anastomotic facial vein). This vessel runs at the level of the alveolar arch of the Mandible and connects the facial vein with the pterygoid venous plexus. Among the anastomoses between the superficial and deep facial veins, the veins of the nasal mucosa and the maxillary sinus are also clinically significant.

6.7 General Anatomy of the Heart

In humans, the heart is a hollow, four-chambered muscular organ whose function is to rhythmically draw in blood (during the relaxation of the chamber walls) and pump it into the circulatory system. The size of an individual's heart typically corresponds to their fist and is conical in shape. The long axis of the heart runs from the apex downward and upward, from left to right, and from anterior to posterior, measuring approximately 12–13 cm. The maximum transverse dimension of the heart is 9–10 cm, and the anteroposterior dimension is 6–7 cm. The average weight of the male heart is 300 g, and the female heart is 220 g (accounting for 1/213 of body mass in men and 1/230 in women).

Normally, the right and left sides of the heart do not communicate with each other. However, the right atrium communicates with the right ventricle, just as the left atrium communicates with the left ventricle. The surface of the heart features sulci (grooves) that serve as external landmarks for defining the boundaries between the heart chambers. Specifically, the coronary sulcus externally separates the atria from the ventricles, while the anterior and posterior interventricular sulci separate the ventricles from one another.

Like any hollow organ, the heart wall consists of three layers. The inner layer, the endocardium, lines the heart chambers and is formed by connective tissue covered with endothelium. The heart valves mentioned above are folds of the endocardium. The middle layer, the myocardium, is composed of Cytology/practical/59.html">Striated cardiac muscle tissue. The myocardium of the atria and ventricles is separated by connective tissue fibrous rings (referred to by some authors as the "cardiac Skeleton"), which are located around the atrioventricular orifices. The atrial myocardium has two layers, whereas the ventricular myocardium has three.

The outer layer of the heart is called the epicardium, which is the visceral layer of the serous Pericardium. The pericardium (pericardial sac) is a closed sac enclosing the heart on all sides, except for a small area at its base where large blood vessels enter and leave the heart. The pericardium consists of two fused membranes: the outer fibrous pericardium and the inner serous pericardium.

The latter, like any serous membrane, consists of parietal and visceral (epicardium) layers, between which lies a slit-like cavity containing 15–20 ml of serous fluid.

Conduction system of the Heart. The uninterrupted, rhythmic activity of the heart is ensured by the cardiac conduction system. This system is a collection of specialized cardiomyocytes (conducting cardiomyocytes, atypical cardiomyocytes, P-cells, pacemaker cells) that differ from contractile cardiomyocytes in size, shape, and ultrastructural organization.

The conduction system of the heart includes the sinuatrial (sinus) node — a cluster of conducting cardiomyocytes located between the openings of the superior and inferior venae cavae and the right auricle. An impulse originates in the sinuatrial node, spreads across the atrial myocardium, and reaches the atrioventricular node, which is situated beneath the endocardium in the lower part of the interatrial septum. The atrioventricular bundle (bundle of His) emerges from the atrioventricular node and, at the beginning of the interventricular septum, divides into right and left branches that ramify within the walls of the respective ventricles.

Normally, the impulse first originates in the sinuatrial node (sinus rhythm) at a rate of 60–70 beats per minute, which is why the sinuatrial node is designated as the primary pacemaker (pacemaker of the first order). In certain cases, when sinuatrial node function is impaired, the atrioventricular node can assume the pacemaker function (secondary pacemaker), resulting in an impulse rate, and consequently a heart rate, of approximately 50 beats per minute.

The cardiac conduction system provides the myocardium with its most vital property — automatism (the capacity for autonomous rhythmic contraction of a denervated heart). Due to this circumstance, heart transplantation surgeries have become possible in recent times.

Innervation of the Heart. The heart is innervated by the Autonomic Nervous system. Sympathetic nerves are branches of the cervical and thoracic cardiac nerves arising from the cervical and thoracic ganglia of the Sympathetic trunk. Parasympathetic nerves are branches of the cervical and thoracic segments of the Vagus nerve.

The autonomic nerves ensure the adaptation of Cardiac Activity to changing environmental demands. The sympathetic system enhances heart activity, whereas the parasympathetic system inhibits it.

Blood Supply to the Heart. The heart is supplied with blood by two coronary arteries: the right and left, which originate from the ascending aorta.

The right coronary artery, upon emerging from the aorta, runs along the right part of the coronary sulcus and descends along the posterior interventricular sulcus. The left coronary artery, upon emerging from the aorta, divides into two branches: the anterior interventricular branch and the circumflex branch. The anterior interventricular branch descends along the anterior interventricular sulcus, where it forms an anastomosis with the right coronary artery near the apex of the heart. The circumflex branch runs along the left part of the coronary sulcus, where it also anastomoses with branches of the right coronary artery.

Thus, the right and left coronary arteries of the heart form two major anastomoses with each other — in the region of the apex of The Heart and within the coronary sulcus. This arrangement is crucial for ensuring an uninterrupted blood supply to the heart during its contraction.

Venous blood drains from the heart: 1 — into the veins of the coronary sinus of the heart; 2 — directly into the right atrium via the anterior cardiac veins; 3 — into the right atrium via the smallest cardiac veins (Thebesian veins).

Certain Developmental anomalies of the Heart. The main congenital heart anomalies are divided into several groups:

1. Anomalies of heart shape, size, and structure.

2. Anomalies of heart position.

3. Anomalies in The Development of the cardiac septa.

4. Anomalies of the cardiac inlets, outlets, and valves.

5. Anomalies in the Water/144.html">Origin of the great vessels.

6. Combined heart defects.

Below are only some of the most frequently occurring or clinically significant developmental defects.

I. Anomalies of heart shape, size, and structure:

1. Acardia (syn.: absence of the heart) — observed only in non-viable fetuses.

2. Macrocardia (syn.: cardiomegaly) — excessive Development of the myocardium. Unknown as an isolated defect.

3. Microcardia — small heart size; unknown as an isolated defect, typically combined with hypoplasia of other organs.

4. Three-chambered heart — division of the right ventricle into two chambers. A very rare defect. It is accompanied by a ventricular septal defect, venous drainage anomalies, and subvalvular pulmonary stenosis.

5. Cor triatriatum — division of the right or left atrium into two compartments by a specialized membrane. Occurs very rarely.

6. Cardiac duplication — the result of dual cardiac primordia. Occurs extremely rarely.

II. Anomalies of cardiac position:

Dextrocardia (syn.: mirror-image dextrocardia) — isolated dextrocardia with a reversed arrangement of the atria and ventricles in the thoracic cavity relative to the Normal Anatomy (cardiac chamber inversion), along with transposition of the great vessels.

III. Anomalies in the development of the cardiac septa:

1. Ventricular septal defect — in most cases, this is a component of complex malformations. The frequency of ventricular septal defects ranges from 12.1% to 39.4%.

2. Atrial septal defect — one of the most common Congenital heart defects, characterized by communication between the right and left atria through the fossa ovalis in the atrial septum.

3. Cor biloculare (two-chambered heart) — absence of both the atrial and ventricular septa. A rare, lethal malformation. It is typically associated with persistent truncus arteriosus.

IV. Anomalies of the cardiac inlets, outlets, and valves:

1. Aneurysm of the aortic sinuses — stretching and thinning of the aortic wall in its ascending portion in the area of the semilunar valve origins, within the sinus region. A rare defect. Congenital sinus aneurysms accompany developmental Disorders of the aortic semilunar valves and, specifically, congenital hypoplasia of the aortic orifice wall.

2. Valvular heart anomalies — in most cases, they constitute a component of complex congenital heart defects.

4. Pulmonary stenosis — isolated narrowing of the pulmonary trunk occurs in 2.5% of cases, in combination with other defects in 14%, and accounts for 8.9% of all congenital heart defects in newborns.

5. Aortic stenosis — observed in 5–10% of cases; in 20% of cases, aortic stenosis is combined with other malformations, such as patent ductus arteriosus, coarctation of the aorta, ventricular septal defect, and pulmonary stenosis.

V. Anomalies in THE ORIGIN OF the great vessels:

1. Truncus arteriosus — persistence of the embryonic arterial trunk, resulting in a single vessel emerging from the heart, positioned over a ventricular septal defect.

2. Transposition of the aorta and pulmonary trunk (syn.: transposition of the great vessels) is characterized by the origin of the aorta from the right ventricle and the pulmonary trunk from the left ventricle. It occurs in 2.2–13.5% of cases.

VI. Combined congenital heart defects:

1. Lutembacher syndrome is a Combination of an atrial septal defect with acquired mitral stenosis.

2. Taussig-Bing syndrome involves transposition of the aorta, sinistroposition of the pulmonary trunk, a high ventricular septal defect, and right ventricular hypertrophy.

3. Pentalogy of Fallot (syn.: Fallot's pentalogy) includes pulmonary stenosis, a high ventricular septal defect, dextroposition of the aortic root, right ventricular hypertrophy, and an atrial septal defect.

4. Tetralogy of Fallot includes pulmonary stenosis, a high ventricular septal defect (up to 2 cm in diameter), secondary dextroposition of the aortic root, and Hypertrophy of the right ventricular wall.

5. Trilogy of Fallot is a combination of valvular pulmonary stenosis, an atrial septal defect, and right ventricular wall hypertrophy.

6.8 Features of Fetal Circulation

The characteristics of fetal circulation are due to the fact that the pulmonary circulation is inactive, as the respiratory organs begin to function only after the newborn's first breath. In utero, the enrichment of fetal blood with nutrients and the removal of carbon dioxide and metabolic waste occur via the Placenta, establishing placental circulation. The Specific features of fetal blood supply include:

1. The pulmonary circulation is non-functional in the fetus.

2. The fetal vascular system contains specific fetal shunts and communications (foramen ovale between the atria, ductus arteriosus, and ductus venosus).

3. Mixed blood circulates through the fetal vessels.

4. Preferential blood supply (blood with a higher relative oxygen content) is directed to the upper body (head) and the liver.

5. Maternal and fetal blood do not mix, being separated by a complex of structural layers known as the placental barrier.

6. The umbilical cord typically contains one vein and two arteries. Oxygenated blood flows to the fetus via the umbilical vein, while deoxygenated blood flows away from the fetus through the umbilical arteries.