[Physiology] Large Intestine Flashcards
what is the legnth of the colon
(1.5 – 1.8 metres)
what are the four parts of the colon
ascending, transverse, descending, sigmoid
what muscle layers are complete in the colon
Circular muscle layer complete but longitudinal muscle layer incomplete
what are the three bands present in the colon
teniae coli (entire length of colon)
what do contractions of the tenia coli result in
pouches (haustra) – puckered appearance
what is the mucosa comprised of in the large intestine
simple columnar epithelium – flat
what is the rectum
Straight, muscular tube (between end of sigmoid colon and anal canal)
what type of mucosa is found in the rectum
simple columnar epithelium
how is the muscularis externa characterised in the rectum
thick compared to other regions of alimentary canal
how much is the distance between distal rectum and anus
2-3cm
is the muscularis externa thicker in the rectum or anus
anal canal as there is an internal anal sphincter
what type of muscle is the external anal sphincter comprised of
skeletal muscle
what type of epithelium is found in the anal canal
simple columnar gradually turning into stratified squamous
what is the role of the colon in nutrient absorption
no role in humans
what does the colon actively do
Actively transports sodium from lumen into blood
what effect does actively transporting sodium from lumen into blood
osmotic absorption of water, dehydrating the chyme producing solid faecal pellets
what takes long residence time in the colon
bacterial colonisation
colonic microflora
10^14 bacteria
Bacterial fermentation of undigested carbohydrate
Short chain fatty acids (energy source in ruminants)
Vitamin K (blood clotting)
Gas (flatus) - nitrogen, CO2, hydrogen, methane, hydrogen sulphide
what is the anus normally closed by
internal anal sphincter and external anal sphincter
internal anal sphincter
smooth muscle under automatic control
external anal sphincter
skeletal muscle under voluntary control
what occurs following a meal
Wave of intense contraction (Mass Movement Contraction) from the colon to the rectum
what is distension of rectal wall produced by
produced by mass movement of faecal material into rectum
once there is a mass movement of faecal material into rectum what is stimulated
mechanoreceptors → defaecation reflex → urge to defaecate
what type of control is the defaecation reflex under
arasympathetic control – via pelvic splanchnic nerves (no sympathetic influence)
describe the parasympathetic control of defacation
Contraction of rectum
Relaxation of internal and contraction of external anal sphincters
Increased peristaltic activity in colon
how are faeces expulsed
↑ Pressure on external anal sphincter - relaxes under voluntary control ⇒ expulsion of faeces
as faeces are expulsed under voluntary control what is there
a voluntary delay in defication
what causes constipation
No absorption of toxins from faecal material following long periods of retention
what is the frequency of bowel movements like in a constipated individual
vary considerably from individual to individual
what are some associated symptoms with constipation
Headaches
Nausea
Loss of appetite
Abdominal distension
what is diarrhoea
Too frequent passage of faeces which are too liquid
what are some causes of diarrhoea
pathogenic bacteria
protozoans
viruses
toxins
food
what is a major killer of children under 5 years of age in developing countries
diarrhoea
how many cases of child diarhoea are there in a year
1500 million
0.5 million deaths
what are examples of Enterotoxigenic Bacteria
vibrio cholerae, Escherichia coli
what does enterotoxigenic bacteria do
Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells
what is increased as a result of maximal turn on of intestinal chloride secretion from crypt cells
H2O secretion increased
what is elevated by enterotoxigenic bacteria
intracellular second messengers:
cAMP
cGMP
calcium
H2O secretion swamps absorptive capacity of villus cells → profuse watery diarrhoea (25 litres per day for cholera)
what is the treatment for secretory diarrhoea
Give sodium/glucose solution
or
Secretion still going ⇒ wash away infection
Oral rehydration therapy (ORS)
