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Flashcards in 125b Absorption Deck (13)

tight junctions

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


absorption of water?

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


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


water and electrolytes absorption

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


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


Na/water absorption - distal colon

simple Na channel allows entry from lumen


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


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)


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)


Na/water absorption - upper intestine

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


Cl absoprtion

mostly passively
transcellularly but most paracellular via Na gradient

also parallel Na/H and Cl/HCO3 exchangers


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


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