Exam 3 Review:  Chapter 23:  Large Intestine Anatomy

large intestine = colon - The portion of the gastrointestinal tract which extends from the ileum to the anus, forming an arch in the abdominal cavity around the convolutions of the small intestine and including the cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal; it is a muscular membranous tube whose wall consists of an inner simple columnar epithelium, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; it functions to complete the final absorption (less than 5%) of nutrients from food, to reabsorb the water added to the chyme by the secretions of the digestive system, and to compress and compact the remaining wastes into feces, which it stores and excretes.  nickname - large bowel

mesocolon - The portion of the abdominal mesentery which holds the lower colon against the dorsal abdominal wall.

cecum - The large blind pouch forming the beginning of the large intestine in the lower right quadrant of the abdominal cavity, and from which the appendix extends; its wall consists of an inner simple columnar epithelium, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; it receives chyme from the small intestine via the ileocecal valve.

appendix - A vestigial process which extends from the lower end of the cecum and which resembles a small worm-like pouch; its wall consists of an inner simple columnar epithelium, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; it has no significant function.

ascending colon - The part of the large intestine which ascends from the cecum to the transverse colon on the right side of the abdominal cavity; its wall consists of an inner simple columnar epithelium, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; it functions to complete the final absorption (less than 5%) of nutrients from food, to reabsorb the water added to the chyme by the secretions of the digestive system, and to compress and compact the remaining wastes into feces.

transverse colon - The part of the large intestine which lies across the upper part of the abdominal cavity; it begins at the right colic flexure as a continuation of the ascending colon and ends at the left colic flexure where the descending colon begins; its wall consists of an inner simple columnar epithelium, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; it functions to complete the final absorption (less than 5%) of nutrients from food, to reabsorb the water added to the chyme by the secretions of the digestive system, and to compress and compact the remaining wastes into feces.

descending colon - The part of the large intestine which descends from the transverse colon to the sigmoid colon on the left side of the abdominal cavity; its wall consists of an inner simple columnar epithelium, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; it functions to complete the final absorption (less than 5%) of nutrients from food, to reabsorb the water added to the chyme by the secretions of the digestive system, and to compress and compact the remaining wastes into feces.

sigmoid colon - The S-shaped section of the large intestine between the descending colon and the rectum on the lower left side of the abdominal cavity; its wall consists of an inner simple columnar epithelium, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; it functions to complete the final absorption (less than 5%) of nutrients from food, to reabsorb the water added to the chyme by the secretions of the digestive system, and to compress and compact the remaining wastes into feces, which it stores prior to excretion.

taeniae coli - The set of three ribbon-like bands of smooth muscle which form the interrupted external layer of the  muscularis of the large intestine; they play a role in haustral churning, peristalsis, and mass peristalsis movements in the large intestine.

haustra - The series of shallow pouches which form the gross structure of the wall of the large intestine; contraction of the smooth muscle in the walls of these pouches assists in extracting the water added to the chyme by the secretions of the digestive system, and compresses and compacts the remaining wastes into feces, a process called haustral churning.

epiploic appendages - Small irregular pouches filled with adipose tissue which are situated along the outer wall of the large intestine beneath the visceral peritoneum.

right colic flexure - The bend in the large intestine which is found at the juncture of the ascending and transverse portions.

left colic flexure - The bend in the large intestine which is found at the juncture of the transverse and descending portions.

rectum - The terminal portion of the large intestine, extending from the sigmoid colon to the anal canal; its wall consists of an inner simple columnar epithelium, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; it functions to reabsorb the water added to the chyme by the secretions of the digestive system, and to compress and compact the remaining wastes into feces, which it stores prior to excretion.

rectal valves - Large transverse folds in the mucosal wall of the rectum which support the weight of the feces to prevent premature release of feces, especially during bouts of flatus (gas expulsion).

anal canal - The terminal section of the rectum where feces are stored prior to excretion; its wall consists of an inner simple columnar epithelium which changes to a stratified sqaumous epithelium in the distal portion, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa;  it discharges feces through the anus with powerful peristaltic waves of contraction.

anus - The opening at the lower end of the large intestine through which solid waste is eliminated from the body by the process of defecation; its wall consists of an inner simple columnar epithelium which changes to a stratified sqaumous epithelium in the distal portion, a lamina propria of loose fibrous connective tissue, a muscularis, and a serosa; its mucous membrane merges with the skin of the perineum exteriorly.

external anal sphincter - The outer rings or bands of skeletal muscle extending from the coccyx to the central tendinous part of the perineum and surrounding the anus immediately beneath the skin; their contraction and relaxation are under voluntary control and are stimulated to initiate or control defecation.

internal anal sphincter - The inner rings of smooth muscle formed by the thickening of the circular smooth muscle of the rectum; their contraction and relaxation are under involuntary control; its action contributes to the control of defecation.

 9.  structures which increase the surface area of the large intestine.

          haustrae  (Note:  technically also the rectal valves, but that is not their purpose)