LARGE INTESTINE

Question 1

Large intestine

Answer 1

• 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

Question 2

Rectum

Answer 2

portion ending at anal canal

has three curves and three infoldings, called the transverse rectal folds (rectal valves)

Question 3

Anal canal

Answer 3

• 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

Question 4

Bacterial flora

Answer 4

populate large intestine

about 800 species of bacteria

digest cellulose and other undigested carbohydrates

body absorbs resulting sugars

Question 5

Flatus

Answer 5

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

Question 6

Absorption and motility

Answer 6

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

Question 7

Feces

Answer 7

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

Question 8

Haustral contractions

Answer 8

occur every 30 minutes

this kind of colonic motility is a form of segmentation

distension of a haustrum stimulates it to contract