Ions and Fluids

Question 1

Osmotic diarrhea

Answer 1

dietary component that is not absorbed

e.g. lactose intolerance (lactose induced), glucose-galactose malabs

Question 2

Secretory diarrhea

Answer 2

secretion of fluid and electrolytes from the intestine
induced by secretagogues

think bacterial infection (enterotoxins) affect the movement of ions

does not affect Na abs

ORS with Glu and Na reverses

Question 3

Nutrient coupled Na transport

Answer 3

secondary active transport
couples Na influx with movement of nutrients downhill (Glucose-SGLT, AA)
in the Jejunum

Leaves lumen more negative (think Cl transport)

not inhibited by cAMP

Question 4

Na-H+ exchanger

Answer 4

NHE3
couples Na uptake with H+ extrusion

increases IC pH, decreases luminal pH

jejunum

stimulated by bicarb excretion into the duodenum
Often associated with Cl-HCO3- exchanger (except in proximal SI)

Question 5

Electorneutral NaCl Absorption

Answer 5

adjacent Na-H and Cl-HCO3- exchangers that are coupled thru pH

Na abs b/w meals: ilieum and colon

*electroneutral bc for each H+, 1 bicarb

bacterial enterotoxin inhibit Na K ATPase via increasing cAMP—>decreased Na abs

Question 6

Electrogenic Na Absorption

Answer 6

epithelial Na channels on apical surface of the very distal colon
**can work against a large CG: rescue mechanism

still dependent Na-K atpase

stimulated by aldosterone

Question 7

passive Cl transport

Answer 7

occurs in jejunum and distal colon

driven by the negative charge left in the lumen by nutrient coupled Na abs or electrogenic Na abs (distal)

Question 8

Cl-HCO3 exchanger

Answer 8

on apical surface (aka DRA exchanger-downregulated in adenoma)
one Cl in, one HCO3 out
mostly in LI

Question 9

Congenital Cl diarrhea

Answer 9

absence of Cl bicarb transporter
extremely high Cl in stool
high plasma bicarb—-> alkalotic
**specific for intestine

Question 10

Cl secretion

Answer 10

Promotes Na secretion

requires activation by secretagogues (low basal levels)
to stimulate Na K pump, Na/K/Cl cotransport, and K+ Channels

+ CFTR to apical surface
*cAMP dependent—>increases CFTR—>increases Cl secretion—>Na secretion—>H2O secretion

Question 11

K abs

Answer 11

Passive transport: Paracellular with water (J/I)

Active: distal colon: H-K pumps (rescue) (Distal colon)

Question 12

K secretion (passive)

Answer 12

passive K secretion in the distal colon

driven by negative lumen, occurs paracelullar
increased by ald due to more negative lumen

think dehydration—>lumen more negative—>increased passive K+ secretion

Question 13

K secretion (active )

Answer 13

colon
basally low
activated by ald and cAMP

Na/K. Na/K/Cl, K leak channels

Question 14

Ca absorption-active

Answer 14

only in duodenum thru villus epithelium
require vitamin D to synthesize calbindin, which binds Ca in the cytosol
extruded on BL surface thru Ca pumps and Na-Ca exchanger

Question 15

Passive Ca absorption

Answer 15

paracellular uptake
Vit D independent
Jejunum and ilium
Occurs when concentrations in the lumen> ICF
**during lactation, plasma Ca is low=more passive uptake

Question 16

Mg abs

Answer 16

Active transcellular: ileum only
independent of Vit D and Ca
**essential for PTH—>decreased Ca transport

passive paracellular uptake in all of SI

Question 17

Iron abs

Answer 17

prefer to take up Ferrous (Fe2+)

Complexed with Vitamin C (increases absorption or reduces 3+ form)

Question 18

Hemochromatosis

Answer 18

exs iron that can accumulate in the organs
women less vulnerable (think menses)

—>cirrhosis, hepatomas, pancreatic damage, bronze pigment …….

tx:Phelbotomize every few months

Question 19

active transcellular fe transport

Answer 19

only in the duodenum

DMT1: cotransport of Fe2+ and H+ into cytoplasm
(also Cd2+ and Pb2+)

Ferric is reduced by Dcytb so tii can be transported

Question 20

Cholera mechanism

Answer 20

toxin binds apical receptors on crypts
increases cAMP
increases Cl- secretion by CFTR
Na follows, and its absorption is mostly inhibited by cAMP

causing secretory diarrhea

Question 21

ORS mechanism

Answer 21

NUTRIENT COUPLED Na REABS IS NOT INHIBITED BY cAMP

-increasing glucose (or AA) with Na in the lumen will cause an increase in Na reabs and reverse the water loss and therefore the diarrhea