Human Anatomy: Part 2 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2008

Special Part
Cardiovascular System, systema cardiovasculare - Venous System
Veins of the Systemic Circulation - Embryonic Development of the Cardiovascular System - Development of Veins (Superior and Inferior Vena Cava and Portal Vein of the Liver)

The main vessels draining Blood from the upper part of the trunk are the superior main (cardinal) Veins, and from the lower part—respectively, the inferior cardinal veins. At The Heart level, on the right and left, the superior and inferior cardinal veins (Cuvierian ducts) fuse to form the common cardinal veins, which open into the venous sinus of the heart.

Blood flow is under favorable conditions in the right Cuvierian duct, whereas in the left it encounters unfavorable conditions. Consequently, the right duct develops into a major vessel, while the left undergoes regression in most of its extent. In connection with the regression of the left Cuvierian duct, the left superior and inferior cardinal veins emptying into it also undergo involution. The remaining part of the left Cuvierian duct forms the coronary sinus of the heart, which receives venous blood from the cardiac veins.

Blood drainage from the left half of the trunk is accomplished through anastomoses that form between the superior and inferior cardinal veins. One anastomosis is established between the superior ones, and three between the inferior ones (Fig. 96 A, B). The left brachiocephalic vein develops from the anastomosis between the superior cardinal veins, while the SUPERIOR VENA CAVA is formed from the segment of the right cardinal vein located below the site of opening of this anastomosis and the right Cuvierian duct.

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Fig. 96 (A, B). Development of the INFERIOR VENA CAVA, azygos vein, and superior vena cava

A - Seventh week. Anastomosis formed between the subcardinal, supracardinal, sacrocardinal, and anterior cardinal veins. 1 - anastomosis between the anterior cardinal veins; 2 - anterior cardinal vein; 3 - common cardinal vein; 4 - supracardinal vein; 5 - posterior cardinal vein; 6 - hepatic segment of the inferior vena cava; 7 - posterior cardinal vein; 8 - subcardinal vein; 9 - renal segment of the inferior vena cava; 10 - left renal vein; 11 - left gonadal vein; 12 - sacrocardinal vein.

B - Venous system at birth. Components of the inferior vena cava. 1 - left brachiocephalic vein; 2 - superior vena cava; 3 - left superior intercostal vein; 4 - azygos vein; 5 - coronary sinus; 6 - hemiazygos vein; 7 - hepatic segment; 8 - renal segment; 9 - left testicular vein; 10 - sacrocardinal segment; 11 - left common renal vein

The azygos vein is formed from the segment of the lower right cardinal vein above the opening of the second (lower) anastomosis, whereas the hemiazygos vein develops from the upper anastomosis.

The segment of the lower right cardinal vein above the second lower anastomosis undergoes regression. The left renal vein develops from this anastomosis, and the left common iliac vein from the third one.

As for the inferior vena cava, its lower section is formed by the segment of the lower right cardinal vein situated between the second and third anastomoses.

The upper section of this vessel, extending from the level of the second anastomosis to its opening into the right atrium, develops independently from the mesenchyme—unlike the veins listed above—meaning it does not arise from pre-existing vessels.

One of the primary sources for The formation of the portal System of the Liver is the vitelline veins, which receive the mesenteric veins and transform into paired vitelline-mesenteric veins opening into the venous sinus of the heart. The rapidly growing liver divides their upper part into microvessels that supply blood to the liver.

The afferent sections of these veins are connected by three transverse anastomoses: the upper one is located within the liver, the middle one lies posteriorly, and the lower one anteriorly to the duodenum (Fig. 97).

Following the regression of certain segments of these vessels, an S-shaped curved vessel (the portal vein of the liver) is formed, which is connected by two branches to the Vessels of the liver (Fig. 98).

Following the regression of the right umbilical vein and the involution of the vitelline veins, an anastomosis forms between the left umbilical vein and the portal vein, ensuring the Blood supply to the hepatic portal system. During The Development of the inferior vena cava, the efferent hepatic veins establish a connection with it (transforming into hepatic veins) and lose their connection with the venous sinus of the heart.

The aforementioned enlarging anastomosis between the left umbilical vein and the portal vein transforms into a ductus venosus (duct of Arantius), which channels excess blood into the inferior vena cava, thereby participating in regulating blood flow from the umbilical vein into either the portal vein or the inferior vena cava.

Postnatal Circulatory Changes

After birth, ligation of the umbilical cord halts the supply of oxygenated blood to the newborn's body. CO₂ accumulates in the blood, serving as a stimulus for the respiratory center. The infant begins to breathe, which is manifested by a cry. Blood from the right ventricle is directed into the Lungs, largely bypassing the ductus arteriosus. Very soon after birth, the duct closes through a reduction process (due to the contraction of circular smooth Muscles), which is reinforced by the thickening of its internal lining.

At the same time, the ductus arteriosus may remain functional for 6–8 weeks, regulating blood flow to the lungs.

Blood flows from the lungs into the right atrium. Blood pressure here increases, the valve of the oval foramen closes it, and it gradually becomes obliterated.

The relatively robust development of the fetal pulmonary vessels prepares its Vascular System for birth. The heart begins to function with two circuits of Circulation.

Congenital Anomalies of The Cardiovascular system

An anomaly is a deviation from the general pattern (atypical development caused by hereditary or intrauterine factors).

A malformation—in most cases, this term is used synonymously with "anomaly." In both instances, developmental variants that fall outside the limits of physiological Variability are implied.

Malformations of the heart and Blood Vessels manifest as functional disorders of vital activity, sometimes incompatible with human life. Congenital defects arise primarily during the intrauterine period when harmful external factors affect the maternal Organism early in Pregnancy. Such children require medical Treatment after birth. The most common Congenital heart defects include atrial septal defect, patent ductus arteriosus, Fallot's triad and tetralogy, aortic stenosis, and pulmonary stenosis.

Fig. 97. Development of the vitelline and umbilical veins during the fifth week. Formation of the plexus around the duodenum, development of hepatic sinusoids, and emergence of left-to-right shunts between the vitelline veins.

Fig. 98. Development of the vitelline and umbilical veins in the third month. Formation of the ductus venosus, portal vein, and inferior vena cava. The splenic and superior mesenteric veins drain into the HEPATIC PORTAL VEIN.

Ventricular septal defect accounts for 30–40% of all congenital heart defects. It is most commonly localized in the membranous part of the septum, and in only 2% of cases in the muscular part.

Atrial septal defect constitutes 7–8% of all congenital heart defects. It should be noted that only relatively large septal defects are clinically significant.

Patent ductus arteriosus causes severe hemodynamic disorders associated with blood shunting from the aorta into the pulmonary trunk.

Aortic stenosis accounts for 5–10% of all congenital heart defects, whereas pulmonary stenosis accounts for 10–15%.

Fallot's triad is a congenital anomaly characterized by pulmonary stenosis, atrial septal defect, and right ventricular myocardial hypertrophy. Fallot's tetrad involves pulmonary stenosis, ventricular septal defect, dextroposition of the aorta (with the aorta overriding the septal defect), and marked right ventricular hypertrophy.

Along with these defects, double aortic arch, sinus venosus defects, right ventricular hypoplasia, valve malformations, and THE ORIGIN OF both the aorta and pulmonary trunk from the left ventricle may also occur.

Anomalies of the Blood Vessels

Arteries may be narrowed, as seen in coarctation (localized narrowing) of the aorta.

Persistence of the right and left 4th pharyngeal arches and dorsal aortic roots can result in the formation of a vascular ring encircling the Esophagus and Trachea. Anomalies in the origin of arteries also occur. For example, the right Subclavian Artery may arise more caudally than the other Branches of the aortic arch. Occasionally, anomalies of venous drainage are observed; for instance, Pulmonary veins may drain into the superior vena cava, left brachiocephalic vein, or azygos vein.

Other venous anomalies include complete absence of the inferior vena cava, duplication of the superior vena cava, and the persistence of left posterior cardinal veins.