small bowel and large intestine Flashcards
large intestine anatomy: recall the anatomy, anatomical relations and structure of the large intestine (and compare to the small intestine)
5 components of large intestine
colon, caecum, appendix, rectum, anal canal
3 main functions of large intestine
reabsorption of water and electrolytes, elimination of waste, microenvironment for gut bacteria
length and width of large intestine
150cm x 6cm - shorter and wider than small intestine
blood supply of large intestine
middle colic artery (branch of superior mesenteric artery) and inferior mesenteric artery; region between two is sensitive to ischaemia
what section does middle colic artery supply
ascending and first 2/3rds transverse portions
what section does inferior mesenteric artery supply
final 1/3rd transverse colon, descending, sigmoid and rectum
how is innervation distributed
parasympathetic via vagus nerve innervates ascending and most of transverse colon, pelvic nerves innovate distal colon
where does sympathetic innervation arise from
lower thoracic and upper lumbar spinal cord - inhibitory function
what does the ileocaecal valve separate
distal lumen from caecum
features of ileocaecal valve
muscular, tonically active, constricted; only relaxes to allow passage of fluid chyme into large intestine; prevents microbiota from migrating into ileum
what is the caecum
blind pouch distal to ileocaecal valve
what is the appendix
thin, finger-like extension protruding from caecum, potentially acting as a safe refuge for gut bacteria
how is appendicitis treated
surgical removal of appendix
where does ascending colon start and finish
starts at ileocaecal valve and runs up right-hand side of body to hepatic flexure
where does transverse colon start and finish
starts at hepatic flexure and runs across abdomen to splenic flexure
where does descending colon start and finish
starts at splenic flexure and runs inferiorly to first bend of sigmoid colon
where does the sigmoid colon start and finish
s-shaped that starts at descending colon and runs until the rectum
what is the rectum and what is its function
dilated portion of colon that acts as storage site for faeces following mass movement in sigmoid colon
difference in histological structure of rectum
transverse rectal folds in submucosa, no taeniae coli in musclaris externa
in rectum, what do transverse rectal folds form
convenient shelves for faeces to occupy until convenient time to defaecate
function of anal canal
control movement of things out of GI tract
what surrounds anal canal
2 anal sphincters, internal and external
features of internal anal sphincter
smooth muscle under central control
features of external anal sphincter
striated muscle under voluntary control
what nerves control external anal sphincter
somatic motor fibres in pudendal nerves
4 unique features of large intestine
appendices epoploicae, longitudinal muscle, circular muscle, nodules of lymphoid tissue
what are appendices epiploicae
fatty tags arising from serosa; perhaps protective function vs intra-abdominal infections
features of 3 longitudinal muscle bands (taeniae coli) in large intestine
equally spaced, relatively thicker than typical longitudinal muscle layers, within muscularis externa, shorter than length of colon so colon forms regular pouches (hastra)
features of circular muscle in large intestine
segmentally thickened; bundles of muscle from taeniae coli (3 longitudinal bands) penetrate circular muscle at irregular intervals to keep them together and anchor them
where are nodules of lympod tissue located in large intestine
solitary nodules (Peyer’s patches in distal small intestine)
what is Hirschsprung’s disease
loss of intramural ganglia
where is myenteric plexus glanglia
concentrated beneath taeniae coli
hormonal/paracrine control: aldosterone
promotes Na+ and water absoprtion
what controls wall regulation
enteric hormonal system
