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 - Fetal circulation

The Prenatal period of fetal development is characterized by the non-functioning of the Pulmonary Circulation. During this stage, fetal Nutrition is provided by the Placenta, whose villi grow into the mucous membrane of the Uterus, plunging into Blood lacunae. Arterial blood flows away from the placenta via the umbilical vein, v. umbilicalis (Fig. 87). It passes through the umbilical cord and enters the Abdominal cavity via the umbilical ring in the anterior abdominal wall. Within the abdominal cavity, the umbilical vein divides into two branches: one branch empties into the portal vein, supplying arterial blood to the Liver, while the second branch—known as the ductus—empties into the INFERIOR VENA CAVA, where arterial blood mixes with venous blood.

This mixed blood flows through the inferior vena cava into the right atrium of The Heart, and a portion of it (25%) passes through the foramen ovale in the interatrial septum into the left atrium. The blood from the inferior and superior venae cavae remains practically unmixed in the right atrium; venous blood from the SUPERIOR VENA CAVA is primarily directed into the right ventricle, whereas oxygen-rich blood from the inferior vena cava passes through the foramen ovale into the left atrium (Fig. 87).

Thus, the blood in the right ventricle is predominantly venous. In the left ventricle, despite a minor influx of venous blood from the Lungs, the blood is more arterial in nature. Upon contraction of the right ventricle, blood is ejected into the pulmonary trunk, truncus pulmonalis, which divides into the right and left aa. pulmonales; however, only a minor fraction of this blood reaches the lungs. Located beneath the aortic arch is the arterial duct, ductus arteriosus (Botallo's duct), through which the greater part of the venous blood from the pulmonary trunk enters the aorta and is distributed throughout the systemic circulation.

The arterial duct empties into the descending aorta, distal to the Water/144.html">Origin of the major vessels supplying the HEAD from the aortic arch. This creates conditions for a more intensive oxygen supply to the Brain. The Abdominal Aorta carries mixed blood, which is less oxygenated than that flowing through the aortic arch. Among the branches supplying the pelvic Organs from the internal iliac artery arises the paired umbilical artery, a. umbilicalis. On the anterior abdominal wall, the umbilical Arteries (right and left) lie along the lateral surface of the Urinary Bladder, converging near its apex to pass through the umbilical ring into the umbilical cord and ultimately reach the placenta. There is no mixing of maternal and fetal blood within the placenta. The placental villi are immersed in the lacunae of the uterine mucosa, through which maternal blood circulates. Nutrients, metabolic wastes, Hormones, and water cross by diffusion between the maternal and fetal bloodstreams in both directions.