Flashcards in Water balance in the GI tract Deck (14):
What is water absorption related to?
It is a passive process
Driven by Na+ (and other solutes)
How can water move?
It can move through transcellular or paracellular routes
What are the mechanisms of movement for sodium ?
Na+/glucose co transporter
Na+/amino acid co transporter
Na+/H+ and Cl-/HCO3 exchange
Apical epithelial Na+ exchange
This occurs in the small intestine the most - Generally postprandially.
What controls the epithelial Na+ channel?
this transporter is found in the colon.
Absorption of Na+ causes negative charge in the lumen.
What is the main sodium transporter?
Na+/glucose and Na+/amino acid cotransport
For each co-transported molecule you get two Na+
This is electrogenic, there a net movement of positive charge.
Therefore there is negative charge left in the lumen. This provides driving force of absorbing anions (Cl-)
(Jejunum and Ileum)
How does Na+/H+ occur?
Occurs in the jejunum/ duodenum
On basal and apical membranes (apical dominant)
This process is coupled with protons being moved out of the cell - raises the local pH+ and provides the driving force for H+ to move out of the cell and Na+ to move into the cell
Describe Na+ and H+ exchange with Cl-/HCO3 exchange ? - Where does it occur?
Chloride moves into the cell.
Occurs in Ileum and Proximal colon
This is electro-neutral
How does Cl- absorption occur?
Occurs passively via transcellular and paracellular
Where does Cl- absorption occurs and how?
Cl--HCO3- exchange (ileum, proximal and distal colon)
parallel Na+-H+ and Cl--HCO3- exchange (ileum and proximal colon)
What is the cellular mechanisms for Cl- secretion?
Occurs at the basal lateral membrane - Usually cells in the crypts and langerhans
What are the processes that are involved on the basolateral membrane?
Na+/K+/2Cl- co-transporter (NKCC1)
K+ channels (IK1 and BK)
Negative change is coming out. Sodium is able to come in.
K+ recycles via K+ channels, but intracellular concentration of Cl- increases providing an electrochemical gradient for Cl- to exit cell via CFTR on the apical membrane
What is overactivity of CFTR related to?
What increases the CFTR secretion of Cl-?
hormones and neurotransmitters
immune cells products