Intestinal Transport Flashcards
What is the enterosystemic fluid cycle?
net movement of fluid into and out of intestinal lumen
Why is it very important to reabsorb secretions delivered to proximal part of SI?
secretory fluids from accessory organs, stomach and intestine itself make up a substantial fraction of ECF volume
What are the major reabsorptive sites of the enterosystemic fluid cycle?
- distal small intestine
- large intestine
What channels are usually closed but will open in response to hormone and neurotransmitters binding basolateral membrane?
Cl- channels
Cholera causes what?
Cl- channels stay open which leads to major loss of Na, Cl, and water
The apical membrane has what channels?
Cl- channels
What ion follows chloride into lumen?
Na+
What are the mechanisms for fluid and electrolyte absorption?
transcellular and paracellular routes
What determines the route of fluid and electrolyte absorption?
permeability of tight junctions between enterocytes
If tight junctions are leaky, what route is used for fluid and electrolyte absorption?
paracellular route
Where are tight junctions leaky?
duodenum and jejunum
If tight junctions are “tight”, what route is used for fluid and electrolyte reabsorption?
transcellular route
Where are tight junctions “tight”?
stomach and colon
What is the major site for Na+ reabsorption?
jejunum
The ileum has an overall net absorption of what?
NaCl
In intestinal absorption, the fluid absorbed is always what?
isosmotic
Na+ absorption in the jejunum occurs via?
Na+ dependent co-transporters in enterocyte apical membrane
The ileum has what exchange in its enterocyte apical membrane?
Cl-/HCO3- exchange
The ileum has what transporter in its enterocyte basolateral membrane?
Cl- transporter
The colon contains what channels in its apical membrane?
Na+ and K+ channels
The synthesis of Na+ channels in the colon is induced by what?
aldosterone
The synthesis of Na+ channels in the colon by aldosterone induction results in what?
increased Na+ absorption and increased K+ secretion
What results in the increased loss of K+ due to increased flow rate of intestinal fluid?
diarrhea
Loss of large volumes of ECF type fluid from GIT causes what?
- decreaseed ECF volume
- decreased intravascular volume
- decreased arterial pressure
High bicarbonate losses relative to Cl losses can lead to what?
hyperchloremic metabolic acidosis with normal anion gap
What are some causes of diarrhea?
- decreased surface area for absorption due to infections or inflammation of SI
- non absorbable solutes cause retention of water in SI lumen (osmotic diarrhea)
- excessive secretion of fluid by crypt cells (secretory diarrhea)
