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Flashcards in Water Balance in the GI tract Deck (40)
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1

What type of process is absoption of water and what is it driven by

PAssive process
By the transport of solutes (particularly Na+) from the lumen of the intestines to the bloodstream

2

How much water enters the GI tract per day

9.3L

3

How much water enters the small intestine per day

8.3L

4

How much water enters the large intestine

1L

5

How much of the water that reaches the large intestine is absorbed

90%

6

What does faeces contain

100ml of water
50ml of cellulose, bilirubin and bacteria

7

What defines diarrhoea

Loss of fluid and solutes form the GI tract in excess of 500ml per day

8

What largely drives the absorption f water in the GI tract

Reabsorption of Na+

9

What is intestinal fluid movement always coupled to?

Solute movement

10

How may water move

Via transcellular or paracellular routes

11

What does the reabsorption of Na+ provide

A local osmotic force for reabsorption of water

12

What are the major mechanisms of postprandial Na+ absorption in the jejunum

Na+/ glucose and Na+/ amino acid co-transport

13

Where does Na+/H+ exchange take place

The apical and basolateral membranes in the jejunum

14

What stimulates the exchange at the apical membrane in the jejunum

Alkaline environment of the lumen due to the presence of bicarbonate from the pancreas

15

What are the primary mechanisms of Na+ absorption in the interdigestive period

Na+/H+ and Cl-/HCO3- exchange in parallel

16

What regulates NaCl+ absorption

Intracellular cAMP, cGMP and Ca2+ which all reduce NaCl absorption

17

A reduction in what is a cause of diarrhoea

NaCl

18

What type of cells mediate electrogenic Na+ absorption in the distal colon

Epithelial Na+ channels (ENaC)

19

What can cause an increase in the the Na+ absorption in the distal colon

Aldosterone

20

What are the 3 actions of aldosterone

opens ENaC
Inserts more ENaC into membrane from intraceullular vesicle pool
Increases synthesis of ENaC and Na+/K+ ATPase

21

How can Cl- be absorbed

Passively via transcellular or paracellular routes

22

What causes the driving force in the lumen of the small intestine

The electrogenic transport of Na+ (Na+/glucose and Na/ amino acid)

23

What causes the driving force in the lumen of the large intestine

Electrogenic movement of Na+ through ENaC

24

At what rate do cellular mechanisms of Cl- secretion occur

At a basal rate often overshadowed by a higher rate of absorption

25

Where does cellular mechanisms of Cl secretion occur

Crypt cells

26

What drives the inward movement of Na+, K+ and Cl- and via what?

Low intracellular Na+
via NKCC1

27

What does the increasing concentration of Cl- provide

an electrochemical gradient for Cl- to exit the cell via CFTR on the apical membrane

28

What provides a voltage depend secretion of Na+ through paracellular pathway

Lumen negative potential

29

What is the overall effect of CFTR

Secretory diarrhoea

30

In normal circumstances, why is there little secreiton of Cl-

The apical CFTR is either closed or not present

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