Intestinal Secretion

Question 1

Name some of the important features of the structure of the gut

Answer 1

serosa
longitudinal muscle
circular muscle
submucosa
mucosa

Question 2

Name the 11 cell types/structures in the intestine (with functions)

Answer 2

villus epithelial cells (absorptive)
brush border (digestion/absorption)
crypt epithelial cells (secretion)
enteroendocrine cells (hormones)
goblet cells (mucus)
lacteals (chylomicrons)
Brunner's glands (mucus)
Paneth cells (lysosomal hydrolases)
stem cells (progenitor cells)
Peyer's patches (lymphoid follicles)
plexus neurons (sm. muscle regulation)

Question 3

What makes up a duodenal cross section?

Answer 3

columnar epithelium
long, flat villi
crypts with Paneth cells
capillaries
lacteals
smooth muscle
Brunner's glands

Question 4

What makes up a jejunal cross section?

Answer 4

longest villi
absence of Brunner’s glands
absence of Peyer’s patches

Question 5

What makes up an ileal cross section?

Answer 5

cuboidal epithelium
short, broad villi
more goblet cells
prominent Peyer’s patches

Question 6

Describe percent efficiency of gastrointestinal tract in absorbing water

Answer 6

jejunum+duodenum = 50%
ileum = 75%
colon = 90%

Question 7

Name the 4 cell types in crypt epithelium and what they do

Answer 7

enterocytes (absorption)
goblet cells (mucus)
crypt cells (secretion)
stem cells (regeneration)

Question 8

Pathology of Cryptosporidium parvum

Answer 8

infect epithelial cells
influx of neutrophils
neutrophils produce TNFa and IL-1B
PGE2 and PGE1 produced

(PGE2 stimulates epithelial secretion directly)
(PGE1 activates neural reflex that stimulates chloride secretion)

Question 9

Pathology of Clostridial difficile toxin A

Answer 9

causes epithelial cell necrosis
necrosis stimulates mast cells
mast cells activate neural reflex that stimulates chloride secretion
mast cells also produce PGE2

(PGE2 stimulates epithelial secretion directly)

Question 10

Pathology of Cholera toxin

Answer 10

toxin binds apical receptors
enteroendocrine cells release 5-HT
neural reflex of 5-HT and VIP secretomotor neurons triggered
VIP secretomotor neurons stimulate chloride secretion

Question 11

Pathology of heat-stable E. coli enterotoxin

Answer 11

toxin binds to brush border and activates guanylyl cyclase
cGMP increases intracellularly
cGMP activates PKG
PKG opens anion channels allows Cl/HCO3- secretion

Question 12

Name some prostaglandin synthetase inhibitors

Answer 12

sulfasalazine
olsalazine
prednisone

Question 13

Name some opioid agonists

Answer 13

loperamide
diphenyoxylate

(avoid in Collie’s!!)

Question 14

Name some serotonin antagonists

Answer 14

ondansetron
granisetron
tropisetron
dolasetron

Question 15

Name some adrenergic agonists

Answer 15

clonidine

Question 16

Name the 10 causes of diarrhea

Answer 16

luminal maldigestion
villous atrophy (gluten, steroids)
enterocyte dysfunction
membrane maldigestion
mucosal disruption (cytotoxic drugs)
hypersensitivity (protein, carbs)
mucosal inflammation (diet, bacteria)
intestinal neoplasia (lymphoma, carcinoid)
lymphatic disorder
motility abnormalities (canine IBD)