Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 273 Venous Return from the Cranium Numerous veins drain the cerebral hemispheres. The superficial cerebral veins and small veins of the brain stem empty into a network of dural sinuses , including the superior and inferior sagittal sinuses, the petrosal sinuses, the occipital sinus, the left and right transverse sinuses, and the straight sinus. The largest, the superior sagittal sinus, is in the falx cerebri. Most of the inferior cerebral veins converge within the brain to form the great cerebral vein, which delivers blood from the interior of the cerebral hemispheres and the choroid plexus to the straight sinus. Other cerebral veins drain into the cavernous sinus with numerous small veins from the orbit. Blood from the cavernous sinus reaches the internal jugular vein through the petrosal sinuses . The venous sinuses converge within the dura mater in the region of the lambdoid suture. The left and right transverse sinuses begin at the confluence of the occipital, sagittal, and straight sinuses. Each transverse sinus drains into a sigmoid sinus, which penetrates the jugular foramen and leaves the skull as the internal jugular vein, descending parallel to the common carotid artery in the neck. Vertebral veins void the cervical spinal cord and the posterior surface of the skull. These vessels descend within the transverse foramina of the cervical vertebrae, in company with the vertebral arteries. The vertebral veins empty into the brachiocephalic veins of the chest. Th Inferior V na Cava The inferior vena cava (IVC) collects most of the venous blood from organs inferior to the diaphragm. A small amount reaches the superior vena cava via the azygos and hemiazygos veins . 20.13 The Hepatic Portal System The hepatic portal system begins in the capillaries of the digestive organs and ends in the liver sinusoids. Blood flowing in the hepatic portal system is quite different from that in other systemic veins because hepatic portal vessels contain substances absorbed by the stomach and intestines. The hepatic portal system delivers absorbed compounds directly to the liver for storage, metabolic conversion, or excretion. The largest vessel of the hepatic portal system is the hepatic portal vein, which delivers venous blood to the liver. The hepatic portal vein receives blood from three large veins draining organs within the peritoneal cavity: • The inferior mesenteric vein: This vein collects blood from capillaries along the inferior portion of the large intestine. Its tributaries include the left colic vein and the superior rectal veins, which drain the descending colon, sigmoid colon, and rectum. • The splenic vein: This is formed by the union of the inferior mesenteric vein and veins from the spleen, the lateral border of the stomach (left gastroepiploic vein), and the pancreas (pancreatic veins). • The superior mesenteric vein: This vein collects blood from veins draining the stomach (right gastroepiploic vein), the small intestine (intestinal and pancreaticoduodenal veins), and two- thirds of the large intestine (ileocolic, right colic, and middle colic veins). The hepatic portal vein forms through the fusion of the superior mesenteric and splenic veins. The superior mesenteric vein normally contributes the greater volume of blood and most of the nutrients. of 368