B5.020 Prework 1 Water and Electrolyte Absorption and Secretion

Question 1

when does diarrhea manifest

Answer 1

both the small intestine and colon have a large reserve capacity for reabsorption, diarrhea manifests when this is exceeded

Question 2

intracellular tight junctions

Answer 2

restrict passive flow across the intestinal epithelium in response to established osmotic gradients

Question 3

function of transcellular proteins

Answer 3

workhorse of intestinal luminal activity
move molecules and water through cells
may work against electrochemical gradients (require energy)
subject to transcriptional and post-transcriptional regulation

Question 4

active transport

Answer 4

requires ATP for movement of molecules across the membrane

Question 5

primary active transport

Answer 5

the ATP driven Na+/K+ stores energy by creating a steep concentration gradient for Na+ entry into the cell

Question 6

secondary active transport

Answer 6

as Na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient into the cell

Question 7

paracellular trans-epithelial transport

Answer 7

movement of solutes and water through tight junctions

dictated primarily by electrochemical gradient

Question 8

3 key points surrounding the process of trans epithelial transport

Answer 8

1. membrane transport proteins drive transcellular transport of ions
2. transport of ions sets up electrochemical gradients
3. electrochemical gradients allow paracellular transport of fluid through tight junctions

Question 9

differences between small intestine and colon absorption functions

Answer 9

small intestine: tight junctions more permeable, larger passive flux of fluids, absorption of nutrients, vitamins, minerals, salt and water
colon: tight junctions less permeable, only absorption of sodium and water favored

Question 10

effect of motility on absorption/secretion

Answer 10

motility/transit time increased: less time for absorption across epithelium
motility/transit time decreased: more time for absorption across epithelium

Question 11

function of villi

Answer 11

absorption
fluid absorption primarily depends on Na+ transport
Na+ may be coupled with Cl-, nutrients, bile acids, and other solutes

Question 12

function of crypts

Answer 12

secretion

primarily follows Cl- and bicarb

Question 13

small intestine ion transport mechanisms

Answer 13

bicarb secretion
electroneutral NaCl absorption
chloride secretion

Question 14

small intestine nutrient/mineral/other transport mechanisms

Answer 14

Na+ coupled nutrient absorption
H+ coupled nutrient absorption
N+ coupled bile acid absorption
Ca2+ absorption
Fe absorption

Question 15

colon ion transport mechanisms

Answer 15

Na+ absorption
K+ secretion and absorption
Cl- secretion
short chain fatty acid absorption

Question 16

mediators that regulate transport mechanisms in diarrhea

Answer 16

infection
inflammation
gut hormones
chemical mediators
enteric nervous system

Question 17

action of Na+/K+ ATPase

Answer 17

on basolateral side of enterocytes
actively drives sodium out of cell and potassium in at a ratio of 3:2
creates a Na+ electrochemical gradient between enterocyte and lumen

Question 18

glucose/AA transport

Answer 18

fostered by the electrochemical gradient established by Na+/K+ ATPase
proteins along apical aspect of enterocyte utilize Na+ transport to facilitate absorption of glucose and AAs

Question 19

SGLT1 transporter in context of diarrhea

Answer 19

preserved function
allows oral rehydration using glucose coupled sodium absorption to promote fluid absorption by coupling sodium with glucose in solution

Question 20

NaCl transport

Answer 20

NaCl is absorbed in conjunction with export of H+ and bicarb
relies on Na+/K+ ATPase to establish gradient
Na+/H+ cation exchanger works in conjunction with Cl-/HCO3- exchanger allowing NaCl reabsorption

Question 21

KCC1

Answer 21

co transport of Cl- and K+

Question 22

CFTR function

Answer 22

coupled import of Na, K, and Cl in basolateral membrane
as intracellular Cl increases, Cl is secreted via apical CFTR
CFTR expression highest in ileum and colon
relevant to secretory diarrhea

Question 23

osmotic diarrhea

Answer 23

solute driven water losses, more prominent in colon
non absorbed solutes create intraluminal concentration gradients that draw in fluid into the lumen and promote fluid loss
carb malabsorption common example

Question 24

secretory diarrhea

Answer 24

crypt secretion leads to more prominent small intestine losses
due to dysregulation of intestinal ion transport which leads to imbalance of ion secretion/absorption
favors secretion, water follows