Anatomy & Physiology

Anatomy & Physiology Study Guide As it proceeds, the hepatic portal vein receives blood from the left and right gastric veins, which drain the medial border of the stomach, and from the cystic vein, emanating from the gallbladder. After passing through liver sinusoids, blood collects in the hepatic veins, which empty into the inferior vena cava. Since blood from the intestines goes to the liver first, with the liver regulating the nutrient content of the blood before it enters the inferior vena cava, the composition of the blood in the systemic circuit is relatively stable despite changes in diet and digestive activity. 20.14 Placental Blood Supply A pair of umbilical arteries, which arise from the internal iliac arteries and travel through the umbilical cord, provide blood flow to the placenta. Blood returns from the placenta in the single umbilical vein, carrying oxygen and nutrients to the developing fetus. The umbilical vein drains into the ductus venosus, a vascular connection to an intricate network of veins within the developing liver. The ductus venosus collects blood from the veins of the liver and from the umbilical vein and empties into the inferior vena cava. When the placental connection is broken at birth, blood flow ceases along the umbilical vessels, and they soon degenerate. However, remnants of these vessels persist throughout life as fibrous cords. 20.15 Fetal Circulation in the Heart and Great Vessels One of the most interesting aspects of circulatory development reflects the differences between the life of an embryo or fetus and that of an infant. Throughout embryonic and fetal lives, the lungs are collapsed; after delivery, the newborn infant must be able to receive oxygen from inspired air rather than across the placenta. Although the interatrial and interventricular septa develop early in fetal life, the interatrial partition remains functionally incomplete until birth. 20.16 Aging Aging affects the blood, heart, and blood vessels. The capabilities of the cardiovascular system gradually decline. As you age, your cardiovascular system undergoes the following major changes: • Age-related changes in blood may include a decreased hematocrit; constriction or blockage of peripheral veins by a thrombus (stationary blood clot), which can become detached, pass through the heart, and become wedged in a small artery (commonly in the lungs), causing pulmonary embolism; and pooling of blood in the leg veins because valves are not working effectively. • Age-related changes in the heart include a reduction in maximum cardiac output; changes in the activities of nodal and conducting cells; a reduction in the elasticity of the cardiac (fibrous) skeleton; progressive atherosclerosis that can restrict coronary circulation; and replacement of damaged cardiac muscle cells by scar tissue.

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