The large intestine Flashcards
What are haustra?
The small pouches of the colon formed by sacculation.
What are the taenia coli?
Three separate ribbons of longitudinal muscle running the length of the colon. Contract lengthwise to produce the haustra.
How does the iliocaecal valve function?
Flutter valve - only opens one way (towards the colon). Opens in response to ileal distension and closes in response to caecal distension.
What is haustration?
Slow contraction of the circular muscle cause segmentation of large bowel contents.
Is peristalsis frequent or infrequent in the large bowel?
Very infrequent - few times per day.
Which nervous system mostly controls large bowel motility?
The intrinsic (enteric) nervous system. Some parasympathetic control.
What is the ‘ileal brake’?
The presence of undigested lipid in distal ileum and proxial colon causes the release of peptide YY which slows gastirc emptying and peristalsis in the small bowel.
How is digestion performed in the colon?
By commensal bacteria.
What are the digestive products of fibre?
Short chain fatty acids such as butyric acid, hydrogen, and methane.
What are the digestive products of urea and amino acids?
Ammonia
What are the breakdown products of bilirubin?
Urobilinogen and stercobilins.
Which amino acids are digested to produce hydrogen sulphide?
Cystiene and methionine
How are short-chain fatty acids absorbed by the colon?
Secondary active transport, via Na+-linked transporter
Important source of energy for colonocytes
How is salt absorbed from the colon?
ENaC channels allow transcellular sodium transport. Paracellular Cl- flux, followed by water. Stimulated by aldosterone.
Which secondary messengers cause the secretion of chloride into the bowel lumen?
cAMP and calcium. C. diff increases calcium, cholera and E.coli increase cAMP - both cause secretory diarrhoea.
