22-4: Lower GI Tract

Question 1

small intestine

Answer 1

long convoluted tube from stomach to colon, where digestion is completed and virtually all absorption occurs

Question 2

what are the three subdivisions of the small intestine, starting from the stomach?

Answer 2

duodenum (first section connected to stomach)
jejunum (middle section)
ileum (final section connected to large instine)

Question 3

duodenum

Answer 3

connected to stomach at pyloric sphincter; the ducts delivering bile and pancreatic juice unite close to duodenum at ampulla of vater. entry of these juices into the duodenum is controlled by sphincter of oddi (which is opened by CCK)

Question 4

Ileum joins to large intestine at ___.

Answer 4

ileocecal sphincter

Question 5

billi

Answer 5

fingerlike projections of the mucosa in the small intestine greatly increasing surface area for digestion and absoroption. Each houses a capillary bed and a modified lymph capillary called a lacteal so absorbed nutrients can enter the blood or lymph directly

Question 6

microvilli

Answer 6

tiny projections of the plasma membrane of each epithelial cell in the mucosa further increasing surface area; sometimes called the brush border

Question 7

intestinal juice

Answer 7

secreted by intestinal gland, mostly water with mucus; slightly alkaline due to bicarbonate ions from pancreas

Question 8

membrane enzymes (brush border enzymes)

Answer 8

digestion enzymes embedded in the plasma membrane of the microvilli, completing the final stages of digestion of carbohydrates and proteins

Question 9

What digestive processes occur in small intestine?

Answer 9

final digestion of carbohydrates, lipids, and proteins; virtually all nutrient absorption

Question 10

what types of motion occur in the small intestine?

Answer 10

segmentation is the most common - mixes chyme with intestinal juice and brings it in contact wit hteh villi

peristalsis - propel chyme forward into the large intestine

Question 11

How are carbohydrates digested?

Answer 11

begin in mouth with salivary amylase, and continues in small intestine with pancreatic amylase - hydrolyze stach into oligo- and disacchrides

brush border enzymes complete breakdown into monosacchrides, which are absorbed directly into the blood of villi by facilitated diffusion and transported to liver by the hepatic portal vein to be stored as glycogen

indigestible carbs (eg. cellulose) don’t have an enzyme to break them down, so they provide bulk to keep things moving through colon

Question 12

How are proteins digested?

Answer 12

begins in stomach with pepsin; pancreatic enzymes chymotrypsin and trypsin continue hydrolysis of proteins into dipeptides in intestine

brush border enzymes complete final digestion into monomers which are absorbed into the epithelial cells of the villi and diffuse directly into the blood of the capillaries

Question 13

How are fats digested?

Answer 13

all lipids digested in small intestine; mechanical digestion by bile allows more surface area for pancreatic lipase to hydrolyze neutral fats into monomers

diffuse into epithelial cells of intestinal mucosa, which are then remade into triglycerides and a protein coat is added, now called chylomicrons

Chylomicrons are too large to enter capillaries, so they enter the lacteals and the lymph stream instead fo the blood

Question 14

How is water absorbed?

Answer 14

most of the fluid is reabsorbed from the lumen of the small intestine into the capillaries of the villi by osmosis (due to the solutes that entered the blood)

Question 15

What is the function of the large intestine?

Answer 15

liquid chyme entering is now very low in nutrients; LI absorbs most of the remaining water, leaving behind a semisolid residue which it will then eliminate from the body as feces

Question 16

What are the regions of the large intestine?

Answer 16

cecum (pouch connected to ileum by iliocecal sphincter that receives chyme from small intestine; appendix is attached, which contains masses of lymph tissue)

colon, divided into ascending colon > hepatic flexure > transverse colon > splenic flexure > descending colon > sigmoid colon

Question 17

tenia coli

Answer 17

longitudinal layer of muscularis, which has been reduced to a ribbon of muscle in large intestine

Question 18

haustra

Answer 18

puckering sacs of colon’s walls

Question 19

rectum

Answer 19

last part of GI tract in the pelvic cavity; last inch is the anal canal which opens to the outside at the anus

Question 20

What sphincters does the anal canal contain?

Answer 20

internal anal sphincter - smooth muscle
external anal sphincter - skeletal muscle

both normally closed

Question 21

bacterial flora

Answer 21

bacteria living in the colon ferment some of the indigestible carbs, producing flatus. They also decompose bile pigments and synthesize vitamin K as well as some B vitamins

Question 22

Is there digestion in the large intestine?

Answer 22

no, no enzymes - most of the remaining water and electrolytes are reabsorbed into the blood, and mucus is secreted for lubrication

Question 23

defecation

Answer 23

the expulsion of feces through anus - stretching of the rectal wall initiates the defecation reflex

Question 24

feces

Answer 24

undigested food (fiber), bacteria, bile pigments, mucus, sloughed off epithelial cells, and water

Question 25

In the defecation reflex, ___ receptors in the rectal wall send impulses to the ___ spinal cord, which triggers a ___ impulse on ___ neurons going to the rectum. This causes ___.

Answer 25

stretch; sacral; motor; parasympathetic; muscles in the wall of the recum to contract and propel feces forward, and the internal anal sphincter to relax and open

Question 26

How does the external anal sphincter open?

Answer 26

as feces enter the anal canal, impulses reach the brain allowing us to decide whether to relax the external anal sphincter

In infants, the defecation reflex causes automatic emptying of the rectum; in potty training, children learn to control their external sphincter

Question 27

diarrhea

Answer 27

any condition that rushes chyme through the large intestine before it has had enough time to absorb the remaining water. Stress or microbes that irritate the mucosa increase intestinal motility, producing liquid feces. prolonged boutes can result in dehydration or electrolyte imbalances

Question 28

constipation

Answer 28

decreased intestinal motility causes feces to remain in the colon for extended periods, and too much water is reabsorbed. the stool becomes hard and difficult to pass. It can be caused by low fluid intake, not enough fiber i nthe diet, lack of exercise, medications, or laxative abuse

Question 29

haustral contractions

Answer 29

slow segementation of the large intestine

Question 30

Valsalva’s maneuver

Answer 30

we aid defecation by closing the glottis (with false vocal cords) and contracting abdominal muscles