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Flashcards in 125b Absorption Deck (13):
1

tight junctions

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

2

absorption of water?

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

3

general scheme for water and NaCl abosrption

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

4

water and electrolytes absorption

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

5

Na/water absorption - ileum and proximal colon

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

6

Na/water absorption - distal colon

simple Na channel allows entry from lumen

7

Na/K ATPase on basolateral side of cell

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




8

K absorption

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)

9

Na/water absorption - jejunum and ileum

sodium dependent glucose import??

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

10

Na/water absorption - upper intestine

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

11

Cl absoprtion

mostly passively
transcellularly but most paracellular via Na gradient

also parallel Na/H and Cl/HCO3 exchangers

12

what determines absorption?

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

13

iron absorbtion

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