Large Intestine Flashcards
Where does the large intestine get its blood from?
- Middle colic artery
2. IMA
Which part of the LI does the parasympathetic nerve innervate?
Ascending and transverse.
Distal colon innervated by pelvic nerves
What separates the distal ileum from the caecum?
The ileocaecal valve.
Separate the LI into 3 parts
Ascending = ileocaecal valve to hepatic flexure
Transverse = hepatic flexure to splenic flexure
Descending = splenic flexure to first bend of sigmoid colon
Describe the sigmoid colon
S shaped part of bowel - descending colon to rectum
Describe the internal anal and external anal sphincters
Internal = smooth muscle, central control.
External = striated, voluntary control. Controlled by pudendal nerves
What are unique features of LI?
- Appendices epiploicae
- Longitudinal muscle - 3 bands which form pouches called Hastra
- Circular muscle - segmentally thickened. Bundles of muscles from taeniae coli penetrate circular muscle at irregular intervals - to keep them together
Invaginations called the colonic crypts have which cell at the bottom?
Stem cells
In the LI, do the mucosa have microvilli?
No.
Enterocytes here have short irregular microvilli
Which cells dominate colonic crypts?
How are these cells stimulated?
Goblet cells
ACh from local nerves
Where are enteroendocrine cells more common, SI or LI?
SI
What do basic colonic contractions do?
Kneading process (minimal propulsion), allows chyme to stay in colon longer for more absorption
What does the anti propulsive contractions of the proximal colon achieve?
Impedes propulsion and keeps food in that region for longer.
Haustral contractions in the transverse and descending colon - localised segmental contractions. Haustral contractions shuffle contents forwards and backwards.
What kind of food promotes mass movements?
How many times a day is there a coordinated mass movement?
1-3 times a day.
High-fibre food promotes mass movement
Urge to defecate comes after a mass movement.
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