Fetal Circulation

The fetus has several adaptations that serve to bypass the lungs, which are not needed to oxygenate the blood. When blood coming from the placenta enters the right atrium, the foramen ovale, a small hole in the septum between the atria, allows some of the blood to go directly into the left atrium, thus bypassing the pulmonary artery. Further, blood pumped out of the right ventricle can shunt directly into the aorta through a short ves-

Aortic arch

Foramen ovale"

Umbilical cord

Umbilical vein (from placenta)

Umbilical cord

Fetal Circulation Model Aortic Arch

Heart

Uterine wall

Placenta

FIGURE 15-7. Fetal circulation and placenta. Color shows relative oxygen content of blood. (Reprinted with permission from Cohen BJ, Wood DL. Memmler's The Human Body in Health and Disease. 9th Ed. Philadelphia: Lippincott Williams & Wilkins, 2000.)

Ductus arteriosus

Heart

Ductus venosus

Descending aorta

Inferior vena cava

Umbilical arteries

(to placenta)

Venous sinus

Uterine /

arteriole Uterine Placental venule capillaries Placental villi

Placenta

Uterine wall

FIGURE 15-7. Fetal circulation and placenta. Color shows relative oxygen content of blood. (Reprinted with permission from Cohen BJ, Wood DL. Memmler's The Human Body in Health and Disease. 9th Ed. Philadelphia: Lippincott Williams & Wilkins, 2000.)

sel, the ductus arteriosus, which connects the pulmonary artery with the descending aorta (see Fig. 15-7). Both of these passages close off at birth when the pulmonary circuit is established. Their failure to close hampers the work of the heart and may require medical attention.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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