Most of the blood of the body returns to the heart by capillaries flowing into venules and finally into veins before reaching the heart. In a portal system blood moves from one capillary system to another capillary system before reaching the heart. The hepatic portal system takes blood from the capillary beds of many of the abdominal organs and carries it to the liver where metabolic processing takes place. The hepatic portal vein receives blood from various veins including the splenic vein, the gastroepiploic vein, the left gastric vein and the colic veins which take blood to the superior mesenteric and inferior mesenteric veins. Once the blood is processed in the liver it enters the systemic circulation by the hepatic veins.
The return of blood from other parts of the pelvic and abdominal cavities does not go through the hepatic portal system but enters the inferior vena cava. The renal veins take blood from the kidneys to the inferior vena cava. The gonadal veins take blood from the testes or the ovaries. The left gonadal vein enters the left renal vein while the right gonadal vein enters the inferior vena cava. The intercostal veins take blood to the hemiazygos and the azygos veins.
Answer Key: a. Azygos v., b. Inferior vena cava, c. Hepatic vv, d. Renal v., e. Posterior intercostal vv., f. Hemiazygos v., g. Gonadal v., h. Hepatic portal v., i. Superior mesenteric v., j. Right colic v., k. Gastric v., I. Splenic v., m. Gastroepiploic v., n. Inferior mesenteric v.
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