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

Special Section
Cardiovascular system, systema cardiovasculare - Venous system
Veins of the systemic circulation - Embryonic development of the cardiovascular system - Development of blood vessels

This section of the textbook discusses the embryonic development of only a few major vascular pathways.

The cranial elongation of the endocardial tubes, which form the inner lining of The Heart (the endocardium), leads to The formation of two ventral aortae. Upon reaching the level of the Pharynx, they curve in a dorsolateral direction to form the aortic arch, and then continue as the dorsal aortae toward the caudal region of the trunk. Initially, these paired Vessels of the primary aorta fuse to form a single median vessel. This fusion begins in the middle of the body and subsequently extends in both cranial and caudal directions.

Two vitelline (mesenteric) aortae branch off from the posterior, unfused segments of the dorsal aortae and extend toward the yolk sac. Within its mesenchyme, they branch into a dense network of small vessels, The Development of which has been described previously. The Veins draining Blood from the yolk sac unite to form two vitelline veins that empty into the venous sinus of the heart.

Although the Blood supply to mammalian embryos is primarily provided by the umbilical (placental) vessels, vitelline vessels also form as a manifestation of recapitulation.

Phylogenetically later is the placental (umbilical) circulatory loop, which establishes The connection between the embryo and the Placenta. Placental vessels form very early and achieve a high degree of development, as they supply the embryo with both oxygen and vital nutrients.

The umbilical (placental) Arteries are a direct continuation of the posterior segments of the dorsal aortae. They course toward the posterior surface of the anterior abdominal wall through the body stalk—which later transforms into the umbilical cord—and branch within the chorionic villi. Oxygenated and nutrient-rich blood returns to the embryonic body via two vitelline veins emptying into the sinus venosus. Later on, over a greater distance, the umbilical veins merge into a single vessel.

Following birth, the placental Circulation is shut down as the connection between the fetus and the placenta is severed, and the Vessels of the Pulmonary Circulation become fully functional.

The Structure/133.html">Discussion of the primary factors characterizing this process must be preceded by An Overview of the facts illustrating the embryonic development of several major arteries and veins.

In vertebrate embryos, six pairs of anastomoses (six pairs of aortic arches) are formed, connecting the ventral and dorsal aortae. Because these arterial trunks are incorporated into the gill arches (see the section on the embryonic Development of the face, digestive, and respiratory systems), they are also referred to as aortic (branchial) arches. Their appearance is a classic example of recapitulation during the development of The Cardiovascular system.

Initially, a single (first) pair of branchial arches develops within the mandibular arches.

Subsequently, five additional pairs of branchial arteries form within each of the branchial arches located caudal to the mandibular arch.

In gill-breathing animals, these arterial arches participate in the Formation of the branchial respiratory apparatus. In higher vertebrates, including mammals, some branchial arches undergo regression, whereas others transform into vessels entirely unrelated to branchial Respiration.

The first two pairs of branchial arteries regress in a six-week-old embryo. The fifth arch is rudimentary and sometimes entirely absent. Consequently, the third, fourth, and sixth pairs of anastomoses remain. The diagrams below (Fig. 95 A, B) illustrate the ventral and dorsal aortae and the connecting branchial arches prior to the regression of their 1st, 2nd, and 5th pairs, as well as after its completion.

The external carotid arteries develop from the segments of the ventral aortae located cranial to the 3rd pair of anastomoses that become freed. The internal carotid arteries form from the 3rd pair and the adjacent segments of the dorsal aortae.

Accordingly, the common carotid arteries develop from the portions of the ventral aortae situated between the 3rd and 4th pairs of anastomoses. The transformation of the 4th pair of anastomoses is asymmetrical: on the left side, the arch enlarges significantly to form the aortic arch, while on the right, it forms the proximal segment of the right Subclavian Artery. The brachiocephalic trunk develops from the section of the right ventral aorta proximal to the 4th arch, giving rise to the right subclavian and right common carotid arteries. The right part of the sixth arch regresses, whereas on the left side, the segment between the dorsal aorta and the Water/144.html">Origin of the pulmonary trunk develops into the ductus arteriosus (Botallo's duct), which shunts blood from the pulmonary circuit to the aorta during the prenatal period.