Large intestine Flashcards
What are taeniae coli?
Three longitudinal muscle bands equally spaced around the colon that mean its easier to contract the circular muscle
What are haustra?
small pouches that give the colon its segmented appearance, because the taeniae coli are shorter than the large intestine
What are the appendicies epiploicae?
Fatty tags
What is the difference between the surface of the small intestine and colon?
Surface of colon is flat and smooth, whereas the small intestine has lots of vili
Why is mucus secreted into the large intestine?
faecal material is compact and less liquidy so mucus needs to facilitate its passage
What secretes mucus onto the surface of the large intestine?
pit glands
how does the ilioceaecal valve open?
Pressure opens valve and allows material to flow through
When does the iliocaecal valve close? why?
When the caecum is expanded, to prevent backflow and prevent bacterial flora from colon entering the ileum
What is meant by the term flutter valve?
one way valve
Is contraction of the colon slow or fast? what is the direction of food?
Slow
Food is moved back and forth
What is a mass movement?
A large peristaltic wave that moves material a long way.
Houstra briefly disappear as all circular muscle is involved in peristalsis
What controls the motility of the colon?
Enteric nervous system
Also enteroendocrine and neurocrine influence from cells releasing 5-HT and Peptide YY
What is the role of peptide YY in motility?
Feeds back to earlier parts of the bowel if movement needs to slow down (i.e. if fats haven’t been absorbed by SI and have moved into the colon) –> ILEAL BREAK
What is the ileal break?
presence of undigested lipids in distal ileum and proximal colon releases peptide YY which slows gastric emptying and small bowel peristalsis
What is the role of gastrocolic and ortocolic reflexes?
Trigger mass movements of the colon
Gastrocolic - triggers colon activity when we eat to clear space
Orthocolic - when you go from horizontal to vertical in the morning it triggers colonic motility
What does the digestion in the colon?
Bacteria - because we can no longer digest anything
What do bacteria digest fibre to?
Short chain fatty acids e.g. methane,
What do bacteria digest urea and amino acids to?
ammonia
What to bacteria digest bilirubin to?
urobilinogen and stercobilins
What to bacteria digest cysteine and methionine to?
Hydrogen sulphide
What do bacteria digest primary bile acids to?
Secondary bile acids
What do bacteria digest conjugated bile acids to?
unconjugated bile acids
What gases are released during fermentation in the colon?
nitrogen
hydrogen
Co2
How are short chain fatty acids picked up?
Active transport using a Na+ linked co transporter
