Large intestine Flashcards
describe the anatomical locations from the start to the end of the large intestine
terminal ileum ileocecal valve caecum ascending colon transverse colon descending colon sigmoid colon rectum
what are haustra
small pouches caused by sacculation (sac formation), which give the colon its segmented appearance
Haustral contractions are slow segmenting, uncoordinated movements that occur approximately every 25 minutes.
what is a barium enema
X-ray used to detect abnormalities of the large intestine via rectum injection
describe the layers of cells from the ,men to the outside in the large intestine
simple columnar epithelium mucous cells intestinal cells intestinal gland muscular mucosal submucosa musculares externa
what is the musclaris external made out of in the large intestine
longitudinal muscle and circular layer
describe the role of the ileoceacal valve
flutter valve is one way
there is periodic relaxation which allows flow to occur
ill distention opens it
caecal distension closes it
what is haustration
slow contractions of circular muscle squeeze contents to and fro as in segmentation
what is mass movement
few times a day there is a peristaltic wave
what is motility in the colon NOT for
moving contents along
what happens to haustra during mass movement
they disappear
what is control of the control one by
intrinsic via the enteric nervous system (some para control)
where do enteroendocrine and neurocrine influences come from in the colon
cells releasing 5-HT and Peptide YY
what reflexes trigger mass movements
gastrocolic and orthocolic
what causes digesting in the colon
bacteria not enzymes
what do bacteria turn these substances into fibre urea + amino acids cysteine/methionine bilirubin primary bile acids conjugated bile acids fermentation
short chain fatty acids such as butyric acid hydrogens nd methane ammonia hydrogen sulphide urobilligen and stercobillins secondary bile acids unconjugated bile acids 1L nitrogen, hydrogen and CO1
how are short chain fatty acids absorbed in the colon
and specific mechanism
secondary active transport via Na+ linked transporter
important souche of energy for coloncytes
lumen has SMCT1 symporter with SCFA and Na
Na out the other side and K back in
how is salt absorbed in the colon and what is the mechanism
ENaC channels apical surface allows transcellular sodium transport - then Na out and K in with K leaking out
paracellular Cl- flux followed by water
stimulated by aldosterone
how is chloride secreted in the colon
NKCC1 on basal surface brings K 2Cl and Na into cell and Cl out via CFTR which requires cAMP and Ca
what causes increase of chloride secretion in colon
cholera and E coli toxins increase cAMP
C difficile toxin increases Ca2+
what does increases in chloride in the colon cause
secretory diarrhoea
what happens to k in the colon
can undergo absorption and secretion
passive secretion exceeds active
balance determined by plasma K, aldosterone and cAMP
what type of muscle is
the internal anal sphincter
external anal sphincter
smooth
skeletal
describe the process of what happens when faeces enters the rectum
feaces enters the rectum and the pressure rises
triggers relaxation of the internal anal sphincter and the urge to defecate
the external anal sphincter contracts
what aids in increasing the rectosigmoid angle
sitting or squatting
relaxation of the puborectalis muscle
what helps to provide motive force for defaecation
rectal peristalsis - triggers colonic mass movement plus raised intraabdominal pressure
what is valsalva manoeuvre
deep breath and contraction of abdominal muscles to aid increases in intraabdominal pressure
