Lecture 17 - SI secretion (Freeman)

Question 1

brunners glands

Answer 1

protects duodenal wall from digestion

Question 2

crypts

Answer 2

pits which secrete almost pure ECF (Cl-) into lumen via cystic fibrosis transmembrane regulator (CFTR) which are immediatley absorbed by thte villi

Question 3

crypt epithelium

Answer 3

= secretory

Question 4

villous epithelium

Answer 4

= absorptive

Question 5

what does cAMP do to the neutral absorptive processes in villus tip cells?

Answer 5

blocks them and stimulates Cl- secretion by crypt cells

Question 6

what does activation of Cl- secretory process in the crypt by enterotoxins cause?

Answer 6

Na movement into lumen thru paracellular route, which causes net secretion of salt and water into intestinal lumen.

therefore secretion is enhanced and absorption is blocked and excessive fluid ends up in the lumen = diarrhea

Question 7

what is a common way to treat diarrhea

Answer 7

the substrate-coupled Na absorptive processes in villi are unaffected. so if glucose is added to an oral electrolyte solution it will enhance water and sodium absorption thru the substrate-coupled Na transporter

Question 8

secretory diarrhea and extracellular space

Answer 8

• net secretion and failed absorption (from enterotoxin) –> diarrhea –> fluid lost from ECS and cant be absorbed from lumen –> depletion of ECS and cause death from dehydration and electrolyte imbalance

Question 9

treatment for secretory diarrhea and extracellular space

Answer 9

glucose (salt pump is not functioning, but the substrate-coupled Na pump is!)

Question 10

systems that control intestinal secretion

Answer 10

neural control
endocrine control
agents that INCREASE NET SECRETION
immune system

Question 11

neutral control

Answer 11

adrenergic stimulation enhances absorption

cholinergic stimulation enhances secretion

Question 12

endocrine control

Answer 12

glucocorticoids increase Na absorption in SI and colon

mineralcorticoids increase Na absorption in colon ONLY

Question 13

agents that INCREASE NET SECRETION

Answer 13

GI transmitters: VIP, prostaglandins, and serotinin

they block coupled salt absorption on the villus and induce Cl secretion in the crypts much as enterotoxins

Question 14

immune system

Answer 14

inflammatory cells can help activate events that will increase secretion of Cl (similar to some enterotoxins)

E.coli does NOT damage cell - ENTEROTOXIN does

Question 15

cystic fibrosis

Answer 15

important example on how secretion of Cl- plays a role in digestion

• most common fatal genetic disease
• body’s exocrine glands secrete an abnormally thick sticky mucus
  cause: no channel to secrete Cl- (and therefore salt and water)
  effects: plugs lumen and breathing