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Gastro > Water Balance in the GI tract > Flashcards

Water Balance in the GI tract Flashcards

1
Q

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

A

PAssive process

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

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2
Q

How much water enters the GI tract per day

A

9.3L

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3
Q

How much water enters the small intestine per day

A

8.3L

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4
Q

How much water enters the large intestine

A

1L

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5
Q

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

A

90%

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6
Q

What does faeces contain

A

100ml of water

50ml of cellulose, bilirubin and bacteria

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7
Q

What defines diarrhoea

A

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

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8
Q

What largely drives the absorption f water in the GI tract

A

Reabsorption of Na+

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9
Q

What is intestinal fluid movement always coupled to?

A

Solute movement

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10
Q

How may water move

A

Via transcellular or paracellular routes

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11
Q

What does the reabsorption of Na+ provide

A

A local osmotic force for reabsorption of water

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12
Q

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

A

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

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13
Q

Where does Na+/H+ exchange take place

A

The apical and basolateral membranes in the jejunum

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14
Q

What stimulates the exchange at the apical membrane in the jejunum

A

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

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15
Q

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

A

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

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16
Q

What regulates NaCl+ absorption

A

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

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17
Q

A reduction in what is a cause of diarrhoea

A

NaCl

18
Q

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

A

Epithelial Na+ channels (ENaC)

19
Q

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

A

Aldosterone

20
Q

What are the 3 actions of aldosterone

A

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

21
Q

How can Cl- be absorbed

A

Passively via transcellular or paracellular routes

22
Q

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

A

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

23
Q

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

A

Electrogenic movement of Na+ through ENaC

24
Q

At what rate do cellular mechanisms of Cl- secretion occur

A

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

25
Q

Where does cellular mechanisms of Cl secretion occur

A

Crypt cells

26
Q

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

A

Low intracellular Na+

via NKCC1

27
Q

What does the increasing concentration of Cl- provide

A

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

28
Q

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

A

Lumen negative potential

29
Q

What is the overall effect of CFTR

A

Secretory diarrhoea

30
Q

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

A

The apical CFTR is either closed or not present

31
Q

What activates CFTR in order for secretion to occur

A

Bacterial enterotoxins
Hormones and neurotransmitters
Immune cells products
Some laxatives

32
Q

Acitvation of CFTR occurs indirectly as a result of what

A

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

33
Q

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

A

opening of channels at the apical membrane

insertion of channels from intracellular vesicles into the membrane

34
Q

What are 5 causes of diarrhoea

A 
Infectious agents - viruses/ bacteria
chronic disease
toxins
drugs
psuchological factors
35
Q

What can diarrhoea result in

A

dehydration
metabolic acidosis
hypokalaemia

36
Q

What are 3 treatment option of severe acute diarrhoea

A

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

37
Q

What are the 3 main causes of diarrhoea

A 
Impaired absorption of NaCl
Excessive secretion
Non-absorbable or poorly absorbable solutes in intestinal lumen 
Hypermotility
Excessive secretion
38
Q

What type of drugs have anti-diarrhoeal activity

A

Morphine- like (opiates)

39
Q

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

A 
Inhibition of enteric neurones
Decreased peristalsis
Increased fluid absorption
Construction of pyloric, ileocaecal and anal sphincters
Increased tone of the large intestine
40
Q

What are 3 major opiates used in diarrhoea

A

Codeine
Diphenoxylate
Loperamide

Gastro (67 decks)

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