Physiology and Pharmacology of fluid balance and motility in the GIT Flashcards
(50 cards)
Typically how much water is absorbed by the small intestine?
8.3 litres
Typically how much water is absorbed by the large intestine?
1 litre enters the large intestine - of which 90% is absorbed
What do faeces normally contain?
100ml of water
50ml of cellulose, bilirubin and bacteria
What is diarrhoea defined as?
Loss of fluid and solutes from the GI tract in excess of 500ml per day
What kind of process is absorption of water in the GI tract?
Passive process
What is absorption of water in the GI tract driven by?
The transport of solutes (Particularly Na+) from the lumen of the intestines to the bloodstream
Driven by the reabsorption of Na
How might water move in the GI tract?
Via transcellular or paracellular routes
What does reabsorption of NA+ provide?
Provides an osmotic force for reabsorption of water through cells into vascular capillaries inside villi
What are the major mechanisms of postprandial Na absorption in the small intestine?
Na+/amino acid co-transport
Na+/glucose co-transport
Describe the 2 co-transporters in the small intestine?
They are secondary active transport
They are electrogenic - collectively the transport of NA+ generates a transepitheial potential in which the lumen is negative (this drives the parallel absorption of Cl-)
Are either of the Na+/glucose and Na+/amino acid cotransport regulated by intracellular cAMP or Ca?
No neither are regulated by intracellular cAMP or Ca
Describe some infections of the GI tract causing diarrhoea?
Viral, bacterial, parasitic
Campylobacter jejuni - commonest strain of bacteria causing gastroenteritis in the UK
Travellers diarrhoea - (enterotoxin producing E.Coli) the most frequent cause
Describe some non-infectious causes of diarrhoea?
IBD, IBS, bile-salts excess, Lactase def.
Psychological factors –anxiety, depression
Hyperthyroidism
Drug induced – Magnesium salts, Cytotoxic drugs, Betablockers
What can lead to C.diff colitis?
Borad spectrum antimicrobials
What part of the GI tract does diarrhoea involve?
Can involve the small or large intestine
Describe excessive section as a cause of diarrhoea?
Caused by cholera toxin (commonly)
cholera toxin enters enterocyte
enzymatically inhibits GTPase activity of the Gs subunit
increased activity of adenylate cyclase
increased concentration of cAMP
cAMP stimulates CFTR
hypersecretion of Cl-, with Na+ and water following
Describe rotavirus as a cause of diarrhoea?
Causes inhibition of Na/K/ATPase and structural damage to mucosal cells leading to reduced absorption
What can diarrhoea result in?
dehydration (Na+ and H2O loss)
metabolic acidosis (HCO3- loss)
hypokalaemia (K+ loss)
may be fatal if severe (e.g. cholera)
What might be some treatment options of severe acute diarrhoea?
maintenance of fluid and electrolyte balance (1st line- life saving)
use of antimicrobial agents (severe infective cases only)
use of antimotility and spasmolytic agents (symptomatic relief in selected cases)
When do you need to give IV rehydration in diarrhoea?
When fluid loss is severe (>10% body weight)
When would oral rehydration therapy be sufficient and describe it?
IT would be sufficient in the majority of cases
It is not designs to stop diarrhoea, it is used to restore and maintain hydration till diarrhoea stops
What is gastroenteritis?
Infectious diarrhoea - inflammation of the GI tract that involves stomach and small intestine
Describe the mechanisms of rehydration therapy and the SGLT1?
2 Na+ bind
Affinity for glucose increases, glucose binds
Na+ and glucose translocate from extracellular to intracellular
2 Na+ dissociate, affinity for glucose falls
Glucose dissociates
Cycle is repeated
What remains intact even insecure gastroenteritis?
Glucose facilitated Na absorption in ileum remains intact
