Water balance in the GI tract Flashcards Preview

GastroIntestinal (GI) > Water balance in the GI tract > Flashcards

Flashcards in Water balance in the GI tract Deck (14):
1

What is water absorption related to?

It is a passive process
Driven by Na+ (and other solutes)

2

How can water move?

It can move through transcellular or paracellular routes

3

What are the mechanisms of movement for sodium ?

Na+/glucose co transporter
Na+/amino acid co transporter
Na+/H+ exchange
Na+/H+ and Cl-/HCO3 exchange
Apical epithelial Na+ exchange

This occurs in the small intestine the most - Generally postprandially.

4

What controls the epithelial Na+ channel?

Aldosterone

this transporter is found in the colon.
Absorption of Na+ causes negative charge in the lumen.

5

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)

6

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

7

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

8

How does Cl- absorption occur?

Occurs passively via transcellular and paracellular

9

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)

10

What is the cellular mechanisms for Cl- secretion?

Occurs at the basal lateral membrane - Usually cells in the crypts and langerhans

11

What are the processes that are involved on the basolateral membrane?

Na+/K+ATPase
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

12

What is overactivity of CFTR related to?

Diarrhoea

13

What increases the CFTR secretion of Cl-?

bacterial enterotoxins
hormones and neurotransmitters
immune cells products
some laxatives

14

What causes the indirect activation of CFTR?

cAMP
cGMP
Ca2+
(This is activated indirectly)