125b Absorption

Question 1

tight junctions

Answer 1

as you move down small intestine and into large intestine, get tighter to prevent water movement

Question 2

absorption of water?

Answer 2

not actively pumped, follows electrolytes (Na) along with Cl (often paracellular route)

Question 3

general scheme for water and NaCl abosrption

Answer 3

Na is transported actively transcellular (across 2 membranes vai basolateral Na/K ATPase) - increases Na concentration on basolateral side and causes water and Cl to follow

Question 4

water and electrolytes absorption

Answer 4

occurs in both small (entirely nutrients) and large intestine (not in mouth and stomach)

Question 5

Na/water absorption - ileum and proximal colon

Answer 5

Na/H exchange makes inside of cell basic which drive HCO3 out via Cl/HCO3 exchangers

net: Na and Cl in AND H and HCO3 out into lumen

Question 6

Na/water absorption - distal colon

Answer 6

simple Na channel allows entry from lumen

Question 7

Na/K ATPase on basolateral side of cell

Answer 7

drives a gradient - low Na inside with negative charge – gradient for Na entry into cell throughout intestine

Question 8

K absorption

Answer 8

occurs passively mostly via gradient
as H20 leaves lumen, K concentration increases which creates a gradient to leave intercellularly

solvent drag also helps

active secretion/absorption - colon; does occur to a small amount; secretion adaptively in response to bacterial toxins (part of secretory diarrhea)

Question 9

Na/water absorption - jejunum and ileum

sodium dependent glucose import??

Answer 9

jejunum and illeum - cotransporters Na/Glucose and Na/amino acids (Na entry allows glucose and aa to be driven against gradient)

Question 10

Na/water absorption - upper intestine

Answer 10

Na/H exchanger - H combines with bicarb from pancreas which allows reabsorption

Question 11

Cl absoprtion

Answer 11

mostly passively
transcellularly but most paracellular via Na gradient

also parallel Na/H and Cl/HCO3 exchangers

Question 12

what determines absorption?

Answer 12

what you eat - very little control

except 1,25 (OH) D3 from PTH (in response to low Ca) – controls Ca uptake

Ca is insoluble so not normally absorbed
Fe is also insoluble

Question 13

iron absorbtion

Answer 13

most not absorbed from enterocyte - crossing both membranes issue

most stored within enterocytes

out of cell is related to plasma concentration with empty spaces on transferritin

heme is absorbed easily