gastroenterology - large bowel Flashcards
What does the large bowel consist of?
colon (ascending, tranverse and descending)
caecum
appendix
recturn
anal canal
What is the caecum?
blind pouch just ditsal to ielocecal valve (connects ileum to colon)
what types of organisms have larger caecum?
herbivors
what is the appendix?
thing extention of caecum , not relevant in humans
what are main function of large bowel?
reabsoprtion of electrolyes and water
elimination of undgiested food and waste
what are the 4 types of colon?
asending- right side runs from caecum to the hepatic flexure, turn of colon by liver
transverse colon - from hepatic flexure to splenic flexture
hangs off the stomach, attached by greater omentum
descending - from splenic flexure to sigmoid colon
sigmoid colon - S shaped descending colon to rectum
What is the blood supply to colon?
proximal transverse - middle colic artery
distal 3rd transverse colon - inferior mesenteric artery
regions between the 2 senstive to ischemia
what is the perotenium?
layer surroding colon
Where are nodules of lymoid tissues common?
walls of distal small intestine - pyere’s patch
large intestine - solitary nodules
what is the strucutre of the peritoneum?
fatty tags - appendices epiploicae
and muscle coat with 3 bands (taeniae coli)
What is function of taenia coli?
large intestine motlity
Why do large intestine have their appearance as it is?
taenia coli are shorter
so forms pouched ovoid segments called hasutra
where does more abosrption take place in colon?
proxmial colon
how do large intestines absorb water?
Na+ and CL- absorbed by exchange mechanisms and ion channels
water follows by osmosis
K+ moves passively into lumen
What is the rectum strucutre?
dilated distal portion of alimentary canal
how is rectum distringushed from colon?
by transverse rectal folds in its submucosa and absence of taenia coli in its musclaris externa
what muscles is the anal canal surronded by?
internal (circular muslce)
external (striated muscle)
anal sphincters
What 4 layers in the large bowel made from?
mucosa, submucosa, muscularis, serosa
which layer habours myetenric plexus?
serosa
which 2 layers have glands?
mucosa and submucosa
what are similarties between mucosal layer of small and large intestine?
entercoytes (abosrb cells) and goblets (secrete mucus) are abudant
a lot of crypts - stem cells
Why does mucosa appear smooth?
as have no villi
what is important about strucutre of entrocyes?
have short irregular microvilli - concerned resportion of salt
what has more goblet cells large or small bowel?
large
Where are they more prevelant in large bowel?
in crypts than along the surface
and increase distally towards rectum
what is charactistic of goblet cell?
apical ends are packed with mucus filled secretions granules awaiting release
Why is mucus imporant?
faiclitates the passage of increasing solid colonic contents and covers bacteria and particulate matter
How are goblet cells stimautled
Ach in parasympatheric and enteric nervous system
Which cells dominate the crypts?
goblet
What about other cells?
no paneth cells
and enteroendocrine cells are rare
glycolayx has no digestive enzymes
what is surface of microvilli covered with?
glycocalyx
how do large bowel move food?
segmental contraction,
what does the proximal colon do?
antipropuslive apttern dominate to retain chyme
what does the transverese and descending colon do?
localised segemental contraction of circular muscle called hasustral contraction
causes back and forth mixing
What increases molitiy of LI?
eating increases frequency
what happens 1-3x a day in large powel?
mass movmement- resemble perisatlic wave
propels fibre that is usually indgestible through colon
What does the parasym control?
ascending colon and most of transverse inervated by vagus
more distal innveravted by pelvic nerves
what is inneravted the external sphincter?
somatic motor fibres in the pudendal nerves
what is the defecation (poo) controlled by?
by saral spinal cord - both reflecx and voluntary actions
What are the steps in defeaction?
reflex sudden distension of walls of rectum
pressure receptors send signals via myenteric plexus to intiate peristalic waves in desneind, sigmoid and rectum while internal anal sphinter inhbited
weak intrinstic
