Water Balance in the GI tract

Question 1

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

Answer 1

PAssive process

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

Question 2

How much water enters the GI tract per day

Answer 2

9.3L

Question 3

How much water enters the small intestine per day

Answer 3

8.3L

Question 4

How much water enters the large intestine

Answer 4

1L

Question 5

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

Answer 5

90%

Question 6

What does faeces contain

Answer 6

100ml of water

50ml of cellulose, bilirubin and bacteria

Question 7

What defines diarrhoea

Answer 7

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

Question 8

What largely drives the absorption f water in the GI tract

Answer 8

Reabsorption of Na+

Question 9

What is intestinal fluid movement always coupled to?

Answer 9

Solute movement

Question 10

How may water move

Answer 10

Via transcellular or paracellular routes

Question 11

What does the reabsorption of Na+ provide

Answer 11

A local osmotic force for reabsorption of water

Question 12

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

Answer 12

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

Question 13

Where does Na+/H+ exchange take place

Answer 13

The apical and basolateral membranes in the jejunum

Question 14

What stimulates the exchange at the apical membrane in the jejunum

Answer 14

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

Question 15

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

Answer 15

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

Question 16

What regulates NaCl+ absorption

Answer 16

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

Question 17

A reduction in what is a cause of diarrhoea

Answer 17

NaCl

Question 18

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

Answer 18

Epithelial Na+ channels (ENaC)

Question 19

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

Answer 19

Aldosterone

Question 20

What are the 3 actions of aldosterone

Answer 20

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

Question 21

How can Cl- be absorbed

Answer 21

Passively via transcellular or paracellular routes

Question 22

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

Answer 22

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

Question 23

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

Answer 23

Electrogenic movement of Na+ through ENaC

Question 24

At what rate do cellular mechanisms of Cl- secretion occur

Answer 24

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

Question 25

Where does cellular mechanisms of Cl secretion occur

Answer 25

Crypt cells

Question 26

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

Answer 26

Low intracellular Na+ | via NKCC1

Question 27

What does the increasing concentration of Cl- provide

Answer 27

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

Question 28

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

Answer 28

Lumen negative potential

Question 29

What is the overall effect of CFTR

Answer 29

Secretory diarrhoea

Question 30

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

Answer 30

The apical CFTR is either closed or not present

Question 31

What activates CFTR in order for secretion to occur

Answer 31

Bacterial enterotoxins Hormones and neurotransmitters Immune cells products Some laxatives

Question 32

Acitvation of CFTR occurs indirectly as a result of what

Answer 32

Of the generation of second messengers such as cAMP CGMP Ca2+

Question 33

The Cl- conductance mediated by CFTR result from what 2 things

Answer 33

opening of channels at the apical membrane | insertion of channels from intracellular vesicles into the membrane

Question 34

What are 5 causes of diarrhoea

Answer 34

``` Infectious agents - viruses/ bacteria chronic disease toxins drugs psuchological factors ```

Question 35

What can diarrhoea result in

Answer 35

dehydration metabolic acidosis hypokalaemia

Question 36

What are 3 treatment option of severe acute diarrhoea

Answer 36

Maintenance of fluid and electrolyte balance Use of anti-infective agents Use of non-antimicrobial antidiarrhoeal agents

Question 37

What are the 3 main causes of diarrhoea

Answer 37

``` Impaired absorption of NaCl Excessive secretion Non-absorbable or poorly absorbable solutes in intestinal lumen Hypermotility Excessive secretion ```

Question 38

What type of drugs have anti-diarrhoeal activity

Answer 38

Morphine- like (opiates)

Question 39

What are some of the actions of opiates on the alimentary tract

Answer 39

``` Inhibition of enteric neurones Decreased peristalsis Increased fluid absorption Construction of pyloric, ileocaecal and anal sphincters Increased tone of the large intestine ```

Question 40

What are 3 major opiates used in diarrhoea

Answer 40

Codeine Diphenoxylate Loperamide