large intestine Flashcards
what are the parts of the large intestine?
- caecum (appendix)
- colon (ascending, transverse, descending and sigmoid)
- rectum
describe the caecum
- most proximal part of the large intestine
- located between the ileum (distal small intestine) and the ascending colon
- acts as a reservoir for chyme which it receives from the ileum
what are the 90* turns in the large intestine called?
- hepatic flexure
- splenic flexure
describe the hepatic flexure
When it meets the right lobe of theliver, it turns 90 degrees to movehorizontally. This turn is known as theright colic flexure(or hepatic flexure), and marks the start of the transverse colon.
describe the splenic flexure
Where it turns another 90 degrees to point inferiorly, this turn is known as the left colic flexure (or splenic flexure).
what are the taenia coli?
3 longitudinal bands of smooth muscle on the outside of the ascending, transverse and descending colon
what are haustrations?
circumferential contraction of the inner muscular layer of the colon
what are appendice epiploicae?
Pouches of peritoneum filled with fat mainly on the transverse and sigmoid colon, though not the rectum
describe the rectum
- most distal segment of thelarge intestine
- important role as a temporary store of faeces
- continuous proximally with thesigmoid colon
- terminates into theanal canal
- the rectum begins as a continuation of the sigmoid colon. Itis macroscopically distinct from the colon, with anabsence of taenia coli, haustra, and omental appendices.
what is the function of rectal valves?
Support the weight of the faeces and slow movement to the anus, which would produce the feeling of wanting to defecate. They contain circular muscle.
what are the Internal haemorrhoidal plexus?
A collection of veins in rectum. These veins communicate directly between the portal and systemic venous system. Any drugs given rectally can act much quicker by bypassing metabolism by passing through the gut.
what is the colon?
The colon is the distal part of the GI tract and extends from the caecum at the right iliac fossa to the anal canal.
what is the ileo-caecal juntion?
- junction between ileum and colon
- Ileo-caecal ‘valve’
- fold of mucosa, allows chyme to pass from S.I. to L.I., but not vice versa.
- the vermiform (‘worm-like’) appendix leads off from the caecum.
- neither caecum nor appendix appear to have any essential function in human beings
what is the epithelium in the large intestine?
simple columnar with goblet cells
what are the similarities in structure of the large intestine to the small intestine?
– Epithelium: simple columnar, with goblet cells
– Intestinal crypts (of Leiberkuhn)
– Mucosal glands (mucus
what are the differences in structure between the large and small intestine?
– No villi in large intestine
– Incomplete layer of longitudinal muscle- Taenia coli in large intestine
– Ring-like arrangement of circular muscle- Haustrae in large intestine
what are the histological layers of the colon?
mucosa
submucos
muscularis externa
what are crypts?
glands found in the epithelial lining of the small intestine and colon. The crypts and intestinal villi are covered by epithelium of 2 types – goblet cells which secrete mucous and enterocytes that secrete water and electrolytes.
what are crypts?
glands found in the epithelial lining of the small intestine and colon. The crypts and intestinal villi are covered by epithelium of 2 types – goblet cells which secrete mucous and enterocytes that secrete water and electrolytes.
what is the function of the colon?
absorption
- approx 0.5-1.0 litre chyme enters L.I. from ileum
- colon absorbs fluid and electrolytes from S.I. chyme
- failure to reabsorb = diarrhoea
what are intestinal bacterial flora?
- in large intestine
roles:
– Ferment dietary fibre (cellulose) and lipid.
– Gases produced (‘flatus’)
– Synthesise some vitamins:
– Vitamin B complex (energy, brain function and cell metabolism- prevents infection, growth of RBCs); vitamin K (fat soluble, and is needed for blood clotting, and helping wounds to heal)
what is the motility in the large intestine?
- Mixing movements
- Similar to segmentation in S.I.
- Contraction of circular muscles
- ‘Squeezing’ action on chyme
- Mainly in caecum & ascending colon
- propulsive movements, peristalsis and mass movements
describe peristalsis in the large intestine
– ‘short range’ peristalsis in transverse and descending colon
– propels semi-solid faecal matter towards rectum
describe mass movements in the large intestine
– Infrequent, more sustained contractions
– usually after meals (gastro-colic reflex)
– Moves chyme/faeces from proximal colon to distal colon
– Rectal distension associated with desire to defaecate
