Flashcards in Physiology and Pharmacology of the Large Intestine Deck (21)
What comprises the large intestine?
colon, caecum, appendix, rectum
How much ileocaecal matter does the large intestine receive every day?
What are the features of the ileoceacal sphincter?
maintains a positive resting pressure
relaxes in response to distension of the duodenum
contracts in response to distension of the ascending colon
What controls the ileocaecal sphincter?
vagus nerve, sympathetic nerves and enteric neurons
What are the primary functions of the large intestine??
absorption of H20, Na, Ck and secretion of K, HCO3 and mucus
absorption of short chain fatty acids
Reservoir of storage
Periodic elimination of faeces
What are the patterns of motility in the large intestine?
haustration, peristalic propulsive movements, defaecation
how often does peristalisis occur in the large intestine?
1-3 times a day triggered by a meal via the gastrocolic response
What controls the gastrocolic reponse?
extrinsic nerve plexuses
What activates defacation?
activation of rectal stretch receptors
What does activation of the rectal stretch receptors trigger?
activation of the afferents in the spinal cord -> parasympathetic efferents -> contraction of sm. muscle -> relaxation of internal anal sphincter
activation of afferents in brain-> urge to poop -> altered firing in efferents to spinal cord
What is diarrhoea defined as?
the loss of 500ml of fluid from the GI tract in a day
What are the principle mechanisms of Na reabsorption in the Gut?
Na-Amino acid cotransport
Parallel Na-H &Cl/HCO3 exchange
What are the causes of diarrhoea?
What is the treatment of severe acute diarrhoea?
maintenance of fluid and electrolyte balance
use of anti-infective agents
use of non-antimicrobial antidiarrhoeal agents
What does diarrhoea cause?
Impaired absorption of NaCl
Non-absorbable solutes in the lumen
How does Cholera affect secretion?
enzymatically inhibits GTPase activity of Ga subunit which increases the AC activity and thus cAMP
cAMP stimulates the CFTR causing hypersecretion of Cl, Na and water
What does rehydration therapy target?
What can be contained within oral rehydration salts?
What are used as anti-motility agents in Diarrhoea?
How do opiates act as anti-motility agents?
inhibition of enteric neurons
decreased peristalsis, increased segmentation
increased fluid absorption
constriction of pyloric, ileocolic and anal sphincters