Anatomy & Physiology

Anatomy & Physiology Study Guide according to the location of the control center: the cephalic phase, the gastric phase, and the intestinal phase. 23.9 The Small Intestine The small intestine is vital for the digestion and as much as ninety percent of nutrient absorption. For the most part, the rest occurs in the large intestine. The small intestine occupies all abdominal regions except the right and left hypochondriac and epigastric regions. The small intestine has three segments: the duodenum, the jejunum, and the ileum. The duodenum is the closest to the stomach and acts as the “mixing bowl” of the digestive process. It receives chyme from the stomach and digestive secretions from the pancreas and liver. From its connection with the stomach, the duodenum curves in a C that encloses the pancreas. A rather abrupt bend marks the boundary between the duodenum and the jejunum . At this junction, the small intestine reenters the peritoneal cavity, supported by a sheet of the mesentery. The ileum , the final segment of the small intestine, is also the longest. The ileum ends at the ileocecal valve , a sphincter that controls the flow of material from the ileum into the cecum of the large intestine. 23.10 Large Intestines The large intestine, also known as the large bowel, has an average length of about 1.5 meters (4.9 ft.) and a width of 7.5 cm (3 in.). It begins at where the ileum ends and continues in a horseshoe-shaped pattern until it stops at the anus. Thus, making itself lie inferior to the stomach and liver where it almost wholly frames the small intestine. The primary functions of the large intestine are to reabsorb water and compact the intestinal contents into feces. The absorption of essential vitamins is liberated by bacterial action and the storage of fecal material before defecation. We can divide the large intestine into three parts: the pouch-like cecum (the first portion), the colon (the largest portion), and the rectum (the last portion. Material arriving from the ileum first enters the cecum , then the ileum attaches to the medial surface of the cecum and opens into the cecum at the ileocecal valve. The cecum collects and stores materials from the ileum and begins the process of compaction. The slender, hollow appendix , or vermiform appendix, is attached to the posteromedial surface of the cecum. Compared to the small intestine the colon is larger in diameter and has thinner walls. It can be divided into four regions: the ascending colon, transverse colon, descending colon, and sigmoid colon. Tributaries of the superior mesenteric and inferior mesenteric arteries deliver blood to the large intestine. Venous blood is collected from the large intestine by the superior mesenteric and inferior mesenteric veins.

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