LI Flashcards
sections
caecum
ascending
transverse
descending
sigmoid
rectum
anal canal
caecum
dilated region with an inf blind end, continuous with the ascending colon superiorly
veniform appendix
fine tube closed at one end which leads to the caecum
contains more lymphoid tissue but composed like the LI
appendix has NO digestive function
ascending colon
passes up from the caecum to the level of the liver where it curves acutely to the left at the hepatic flexure become the TC
transverse colon
extends across the abdominal cavity, infront of the duodenum and stomach to the spleen- splenic flexure which curves acutely down to the descending colon
descending colon
passes down the las curving towards midline
sigmoid
found at the iliac crest level continues to become the rectum
anal canal
leads from the rectum to the exterior
two sphincter muscles, control the anus,
internal: smooth muscle under autonomic control
external sphincter: formed by skeletal muscle under voluntary control
taenia coli
three bands of longitudinal tissue run alongside the caecum and the colon, stopping at the junction of the SC and rectum, these give a sacculated appearance
how are anal sphincters formed
thickened circular muscles
where is there the most amount of lymphoid tissue
submucosal layer
non specific defence against microbes
mucosal layer of the colon and upper rectum
goblet cells within the simple tubular glands
what is the anal canal lined with
stratified squamous epithelium continuous with the mucous membrane lining above the rectum
merges with the skin beyond the anal sphincter
upper portion of the upper canal forms 6-10 vertical folds anal columns, each column contains a terminal branch of superior rectal artery and vein
four functions
defeacation
microbial activity
mass movement
absorption
absorption
contents passed through the caecum are fluid, water absorption occurs, this continues until a semi solid consistency is reached
mineral salts, vitamins and some drugs are absorbed into the blood capillaries
microbial activity
heavily colonised by bacteria which synthesises vitamin K and folic acid
gas = nitrogen, hydrogen, carbon dioxide, methane
mass movement
no peristalsis occurs however at some sections, a strong wave of peristalsis occurs which sweeps contents along the TC into the descending sigmoid colon
gastro-colic reflux
combination of stimulus and response
defection
mass movement travels into the rectum from the SC
nerve ending are stimulated by stretching
external anal sphincter is under conscious control through the pudenal nerve
involves involuntary contractions of rectum and relaxation of internal anal sphincter
contraction of abdominal muscles and lowering of the diaphragm increases intra-abdominal pressure assisting defection
repeated suppression of this reflux could lead to constipation as more water is reabsorbed.
where does is begin
right iliac fossa
arterial blood supply
superior and inferior mesenteric arteries
superior mesenteric artery supplies the caecum, ascending and most of the TC
inferior mesenteric artery supplies the remaining colon and proximal art of the rectum
middle and inferior rectal arteries supply the distal part of the rectium and anal, and internal iliac arteries
venous drainage
superior and inferior mesenteric veins drain from parts supplied by the arteries.
these veins join the splenic and gastric veins to form the portal vein
veins which drain from the distal part of the rectum and anus goin the internal iliac veins, blood then drains to the IVC bypassing portal circulation
why is faeces brown
stereobilirubin
faeces consists of
dead and live microbes
water
mucus secrete by the LI lining aiding lubrication of faeces
fibre
epithelial cells shed from the walls
why is there fibre in faeces
so it is bulky enough the stimulate defection
