Large Intestine Structure and Function Flashcards
Parts of large intestine
Ilemn Ileocaecal valve Caecum Colon Rectum
Parts of colon
Ascending
Transverse
Descending
Sigmoid
Mucosal epithelium
Simple columnar
Lubrication for movement of faeces
Large, straight crypts lined with large number of goblet cells
Rectum
Straight, muscular tube (between end of sigmoid colon and anal canal)
Mucosa of rectum
Simple columnar epithelium
Muscularis externa of rectum
Thick compared to other regions of alimentary canal
Muscularis of anal canal campared to rectum
Thicker => contains internal anal sphincter
External anal sphincter tissue type
Skeletal muscle
Epithelium of anal canal
Simple columnar to stratified squamous
Nutrient absorption role of colon
No important role in humans
Function of colon
Actively transports sodium from lumen into blood => osmotic absorption of water => dehydration of chyme => solid faecal pellets
Bacterial colonisation in colon as a result of
Long residence time - bacterial fermentation of undigested carbohydrate
Colonic microflora resulting in
Short chain fatty acids (energy source in ruminants)
Vitamin K (blood clotting)
Gas (flatus) - nitrogen, CO2, hydrogen, methane and hydrogen sulphide
Control of internal anal sphincter
Smooth muscle under automatic control
Control of external anal sphincter
Skeletal muscle under voluntary control
Urge to defaecate as a result of
Distension of rectal wall produced by mass movement of faecal material into rectum rsulting in mechanoreceptors triggering defaecation reflex
Control of defaecation reflex
Parasympathetic control via pelvic splanchnic nerves
Constipation resulting in
No absorption of toxins from faecal material following long periods of retention
Symptoms associated with constipation
Headaches
Nausea
Loss of appetite
Abdominal distension
Abdominal distension
When substances, such as gas or fluid, accumulate in the abdomen causing its expansion
Causes of diarrhoea
Pathogenic bacteria Protozoans Viruses Toxins Food
Enterotoxigenic bacteria
Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells
Increasing H2O secretion
Act by elevating intracellular second messengers:
cAMP
cGMP
calcium
H2O secretion swamps absorptive capacity of villus cells
Resulting in profuse watery diarrhoea
Treatment of secretory diarrhoea (enterotexigenic bacteria)
Enterotoxins don’t damage villus cells
Give sodium/glucose solution
Drive water absorption => rehydration
