Digestion and Abs 2 (Johnson) Flashcards
Sources of fluids entering small intestine?
diet saliva gastric secretion bile pancreatic secretion sm intestinal secretion
Fluids are absorbed by:
dueodenum/jejunum (4L)
ileum (3.5L)
colon (1.4L)
What is NOT present in feces?
almost all nutrients, electrolytes, and all but 100-200mL fluid)
By what mechanism are water and electrolytes absorbed?
transcellularly
paracellularly (via tight junctions)
Duodenum tight junctions are very (loose/tight)
loose–water easily absorbed
Tightest tight junctions are found in the:
colon
What are the fat-soluble vitamins?
ADEK
What frees up B12 during absorption?
pepsin
Binds B12 in stomach (protective)
heptacorn
What happens to B12 once it passes in to duodenum?
heptacorn degraded, intrinsic factor complexes with B12
What is the function of intrinsic factor?
binds B12 in duodenum, protects it in passage from small bowel to ileum
in ileum, intrinsic factor is recognized by its carrier and allows for uptake of B12
All mechanisms for Na+ absorption depend on:
gradient established by Na/K/ATPase located at basolateral membrane
How is Na+ taken up from the mucosal solution at apical membrane? (4 mechanisms)
- Na+ channel, most likely located in colon
- Na+ w/ sugar or amino acid
- Na+/Cl- cotransport (elec neutral)
- Na+/H+ exchange (elec neutral)
In the COLON,
HCO3- is exchanged for ____, which is then:
Cl-
reabsorbed into serosal solution w/ H+
Why is stool H2O alkalinic?
the colon exchanges Cl- for bicarb, so high levels of bicarb in feces
What mechanism of electrolyte absorption predominates in the small intestine?
paracellular
The amount of K excreted depends on:
How + why?
aldosterone: activates Na channels and increases # of Na/K/ATPases in basolateral membrane
goal = conserve Na
In the COLON,
K+ is exchanged for ____
Na+
K excreted, Na absorbed
How is water absorption different in the prox small bowel versus the colon?
colon = tight junctions, not much water abs
PSB = “leaky” and water follows Na via osmosis
By the time that small amount of water is excreted, it is (hypo/hyper/iso)-tonic
iso
due to bacteria
The small intestine secretes ___ liter of H2O per day via (what structural component?).
1
crypts
(probably to keep chyme liquidy)
How does secretion of water from crypt cells occur (in terms of ions and water)?
On apical/serosal side:
- -Na is actively pumped out of cell, K diffuses out via channel
- -Na+/K+ brought back in along with 2 Cl-
On basolateral/mucosal side:
- -Cl- leaves cell via channels (2 types)
- -Na+ diffuses paracellularly
NaCl secreted, and H2O follows!
What types of Ca channels are located in crypt cells on apical membrane?
cAMP-activated
Ca-activated
What causes watery diarrhea in bacterial infections?
bacterial toxins (like in cholera) stimulate adenylate cyclase; cAMP then activates Cl- channel (this drives NaCl and H2O secretion)
