Large Intestine Structure & Function Flashcards
Order of the large intestine:
Caecum (with vermiform appendix coming off) Ascending Colon Transverse Colon Descending Colon Sigmoid Colon Rectum Anal Canal Anus
What is the caecums function?
Its a blind ended sac acting like a big fermentation sac, much bigger in full herbivores who need bacteria to break down cellulose more
Where is the appendix and what does it do?
Most often retrocaecal but varies
No real known function- but they are associated with lymph nodes so may have an immune function
How long is the colon?
1.5m
Whats different about the muscularis Externa of the large intestine?
The longitudinal muscle layer isn’t complete but instead comes in three strips that run the length of the colon called teniae coli
The colon has a quilted or puffa jacket appearance, what produces this?
The 3 teniae coli, when they contract the circular muscle layer is forced out the gaps and produces the haustra or sacculations.
Whats different about the mucosa of the large intestine to small?
SI has villi
Whats different about the crypts in the large intestine to the small intestine?
They’re much longer in the colon and lined with goblet cells to lubricate movement of faeces
What is the rectum?
A straight muscular tube connecting the sigmoid colon and anal canal.
It has a thicker muscularis externa than most of the canal
What is the anal canal?
A short 2-3cm channel.
Its muscularis externa forms the internal anal sphincter (IAS).
Where is the external anal sphincter, and what is it made from?
In the anal canal, distal to the internal anal sphincter.
Its made of skeletal muscle and so is voluntarily controlled
How does epithelium change leaving the anal canal?
IT changes from simple columnar to stratified squamous like the skin.
What is the main function of the colon?
Actively absorbing sodium in order to take up water.
A huge amount of bacteria exists in the colon, (colonic microflora) why?
The long residence time of faeces allows extensive bacterial colonisation
What are the roles of colonic microflora?
- Breakdown undigested carbohydrates (cellulose) to short chain fatty acids which we use for energy
- Also produce vitamin K which we use for blood clotting