Book 4 - Self Instructional Manual for Cancer Registrars - SEER ...

Small IntestineThe small intestine is a tube measuring about 2.5 cm. in diameter and over 20 feet (600 cm.) inlength coiled in loops which fill most of the abdominal cavity. It has three divisions--duodenum,jejunum, and ileum:• The duodenum is just below the pyloric portion of the stomach and is about 25 cm. long andshaped somewhat like the letter C. It receives chyme from the stomach, bile from thegallbladder, and pancreatic secretions from the pancreas. The common bile duct andpancreatic duct join the duodenum at the ampulla of Vater. The duodenum becomes thejejunum where the tube turns forward and downward.° The jejunum continues for over 200 cm. and then becomes the ileum, although there is nodemarcation between the two divisions.° The ileum is over 300 cm. long and joins the large intestine at the ileocecal valve.The wall of the small intestine is composed of the same three main layers of tissue as the rest ofthe gastrointestinal tract and is covered with serosa. Small aggregates of lymphoid tissue calledPeyer's patches are found in the lamina propria of the small intestine, principally in the distal ileum.The small intestine completes the digestion of the material received from the stomach and movesit along in peristaltic waves to the colon. Increased epithelial surface needed for absorption isprovided by circular folds and villi.1 The absorbed material which reaches the blood stream via theintestinal capillaries and lymphatics includes 1) water, 2) carbohydrates, 3) fat, and 4) protein.The lymphatic drainage of the small intestine is to lymph nodes along the branches of the superiormesenteric and hepatic arteries. Duodenal nodes, in particular, may be described in terms of theirlocation in relation to adjacent organs, such as, the stomach (pyloric), gallbladder (cystic), bile ducts(pericholedochal), pancreas (pancreaticoduodenal) and ampulla of Vater. The terminal ileum drainsto posterior cecal and ileocecal nodes of the superior mesenteric group.Malignantand Benign TumorsIn spite of the relatively long length of the small intestine, tumors are rare. Thirty-five percentof all tumors of the small intestine are benign. Only one-fourth of all tumors in this site areadenocarcinomas, most frequently found in the duodenum. Lymphoma is the next most frequentlydiagnosed tumor of the small intestine with carcinoid tumors (argentaffinomas) and leiomyosarcomasaccounting for the remainder.lvillus--(plural - villi)--A small vascular process or protrusion, usually covered by epithelium,especially such a protrusion from the free surface of a membrane.215