Large intestine structure and function Flashcards
Anatomy of the colon
Begins at ileocaecal sphincter Ascending Transverse Descending Sigmoid The circular muscle layer is complete The longitudinal muscle layer is not Teniae coli- into haustra Crypts are a lot longer than in SI and contain goblet cells needed for the lubrificationof faeces
What are teniae coli?
Three bands which are continuous in the colon
What are haustra?
Contraction of the teniae coli leads to the formation of haustra- puffa jacket appearance
Epithelium in the colon
Simple columnar
Epithelium in the rectum
simple columnar
Rectum anatomy
- Straight muscular tube which connects the sigmoid colon to the anal canal
- Muscularis externa is very thick
Anal canal epithelium
From simple columnar to stratified squamous
Anatomy of the anal canal
- Very thick muscularis externa: internal anal sphincter
- Skeletal muscle: external anal sphincter
Role of the colon?
-Absorption of H20 AND Nacl into the blood- concentrates faeces.
H20 follows the uptake of Na
-Large gut flora= breakdown of nutrients into FA, gas (Flatus) and vitamin K (used for blood clotting)
What is the number of colonic flora in the gut compared with the number of cells in the body?
gut flora= 10^14
Cells in the body= 10^12
How does defection occur
Ileocaecal sphincter reflex pushes chyme into the LI
When build up occurs: mass movement contraction= massive peristaltic movement of chyme into the rectum
Mechanoreceptors in the rectum detect change- defection reflex
Rectum contracts
IAS relaxes
EAS contracts
when enough pressure builds up- EAS relaxes
Control of the IAS and EAS
IAS- autonomic control
EAS- voluntary control
Control of defaecation reflex?
Parasympathetic control through pelvic-splanchnic nerves.
