LARGE INTESTINE Flashcards
Describe the gross and microscopic anatomy of the large intestine and its function
Large intestine
- begins at cecum inferior to ileocecal valve
- appendix attached to lower end of cecum
- densely populated with lymphocytes and is a significant source of immune cells
- ascending colon, right colic (hepatic) flexure, transverse colon, left colic (splenic) flexure, and descending colon frame the small intestine
- sigmoid colon is S-shaped portion leading down into pelvis
Rectum
portion ending at anal canal
has three curves and three infoldings, called the transverse rectal folds (rectal valves)
Anal canal
- final 3 cm of the large intestine
- passes through levator ani muscle and pelvic floor terminates at the anus
- anal columns and sinuses—exude mucus and lubricant into anal canal during defecation
- large hemorrhoidal veins for superficial plexus in anal columns and around orifice
Bacterial flora
populate large intestine
about 800 species of bacteria
digest cellulose and other undigested carbohydrates
body absorbs resulting sugars
Flatus
intestinal gas
average person produces 500 mL per day (flatus) from 7 to 10 L of gas present but reabsorbed
hydrogen sulfide, indole, and skatole produce odor
others are odorless
Absorption and motility
large intestine takes about 12 to 24 hours to reduce the residue of a meal to feces
does not chemically change the residue
reabsorbs water and electrolytes
Feces
consist of 75% water and 25% solids, of which 30% is bacteria, 30% undigested fiber, 10% to 20% fat, small amount of mucus, and sloughed epithelial cells
Haustral contractions
occur every 30 minutes
this kind of colonic motility is a form of segmentation
distension of a haustrum stimulates it to contract