In this schematic drawing of the circulatory system, note how the hepatic portal vein drains one set of the capillaries and leads to another set. A similar relationship exists in the kidneys.

Similarly, the liver helps regulate blood concentrations of recently absorbed amino acids and lipids by modifying their molecules into forms cells can use, by oxidizing them, or by changing them into storage forms. The liver also stores certain vitamins and detoxifies harmful substances.

Blood in the hepatic portal vein nearly always contains bacteria that have entered through intestinal capillaries. Large Kupffer cells lining the hepatic sinusoids phagocytize these microorganisms, removing them from the portal blood before it leaves the liver.

After passing through the hepatic sinusoids of the liver, the blood in the hepatic portal system travels through a series of merging vessels into hepatic veins. These veins empty into the inferior vena cava, returning the blood to the general circulation.

Other veins empty into the inferior vena cava as it ascends through the abdomen. They include the lumbar, gonadal, renal, suprarenal, and phrenic veins. These vessels drain regions that arteries with corresponding names supply.

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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