Large Bowel Flashcards
(26 cards)
Facts about the caecum
Blind pouch just distal to the ileocecal valve - larger in herbivores
Facts about the appendix
Thin, finger like extension of the caecum - not physiologiclaly relevant in humans
What are the principal functions of the large bowel
Reabsorption of electrolytes and water
Elimination of undigested food and waste
1.5m long 6 cm diameter
Differen parts of the colon
Asencding colon runs from caecum to hepatic flexure
Transerse colon runs from hepatic flexure to spelnic flexure, hangs off the stomach - attached by a wide band of tissue called greater omentum
Descending colon - splenic flexure to sigmoid colon
Sigmond colon runs from descneding colon to rectum
Blood supply of colon
Supplied with blood by the middle colic artery (branch of superior mesenteric artery)
Distal third of colon perfused by inferior mesentric artery
Region between two is sensitive to ischemia
What is taenia coli used for
Large intestine motility
What are teh nodules of lymphoid tissue
Small intestine - peyers patches
Large intestine - solitary nodules
What causes haustra
Taenia coli shorter than small intestine
Colon function
Colon absorbs electrolyes and water
Na and Cl absorbed by exchange mechanisms
Water follows by osmosis
K moves passively into lumb
Large intestine can reabsobre 4.5 litres - above this threshold results in diarrhoea
How is the rectum different to the colon
Transverse rectal folds in submucosa and absence of taenia coli
What is the mucosal organisation of large bowel
Mucosa appears smooth at gross level because no villi
Enterocytes have short irregular mcirovilli with reabsorption of salts
Crypts dominated by goblet cells
Goblet cells in large bowel
Mucus - facilitates passage of increasingly solid colonic contents
Acetylcholine - stimulates goblet cell secretion
Difference between large bowel and small bowel
No paneth cells and enteroendocrine cells
Glycocalyx do not contain digestive enzymes
What are the muscle layers of the large bowel
Circular muscles segmentally thickened
Logitudinal laeyrs concentrated in three badns -taenia coli
Between taenia longitudinal layer is thin
Bundles of teniae coli penetrate circular layer at irregular intervals
Is movement of large bowel more or less complicated than small intestine
More complicated
How does the chyme move in the large bowel
Kneading process - 5-10cm/hr
Promotes absorption of electrolytes and water
Proximal colon- antipropulsive patterns domiante to retian chyme
Increase in frequency following a meal
Short propulsive movements every 30 mins
What is the mass movement in the large bowel
1-3 times daily
Propel contents 1/3-3/4 of length
Food that contains fibre promots rapid transport (through colon)
What is the large bowel innervated by
Parasympathetic - Ascending colon and transfverse - vagus
Distally innervated by pelvic nerves
Sympathetic - lower thoracic and upper lumbar spinal cords
External anal sphincter controlled by somatic motor fibres in pudendal nerves
Afferent sensory neurons detect pressure
Enteric nervous system
Myenteric plexus ganglia
How is the defecation reflex controlled
Sacral spinal cord - both reflex and voluntary actions
Distension of walls of rectum - pressure receptors send signals via myenetric plexus to initiate peristaltic waves
Internal anal sphincter inhibited
Weak intrinsic signal augmented by autonomic reflex
External anal sphincter under voluntary control
Urge resisted, sensation subsides
Why is rectum known as the socila part
Distinguish between solid, liquid and gas
Can identify what can be passed appropriately in what circumstance
What is faeces made up of
150g/day adult
two thirds water
solids: cellulose, bacteria, cell debris, bile pigments, salts (k+)
Bile pigments give colour
Bacterial fermentation gives odour
How much does the microbiome of an average human weigh
1.5KG
Role of the intestinal flora
Sythesis and excrete vitamins
Prevent colonization by pathogens by competiting for attachment sites or for essential nutrients
Antagonize otehr bacteria through production of substances which inhibit non-indigenous species
Stimulate production of cross-reactive antibodies which can cross react with certain related pathogens prevent infection
Stimulate development of certain tissues - caecum and lymphatic tissues
Fibre can be broken down by bacteria
Produces short cahin fatty acids - regulat gut hormone, energy source, influence food intake, insulin sensitivity
What are the types of flora
Bacteroides - gram negative, anaerobic, non-spore forming bacteria - initiation colitis and colon cancer
Bifidobacteria - gram positive, non-sporeforming, lactic acid bacteria, frienly bacteria which prevents colonisation of other bacteria
