Large Intestine Structure and Function Flashcards
what is the caecum?
a blind sac at the start of the large intestine (large in herbivores)
name the four parts of the large intestine
> ascending
transverse
descending
sigmoid
what layer of muscle is complete throughout the large intestine?
the circular layer
what do contractions of teniae coli produce in the large intestine?
pouches - haustra
how many bands of teniae coli are there in the large intestine?
three
what type of epithelium makes up the mucosa in the large intestine?
simple columnar
describe the crypts in the large intestine
they are large and straight with a large number of goblet cells
describe the anatomy of the rectum
it is a straight, muscular tube between the end of the sigmoid colon and the anal canal
what epithelium is found in the rectum?
simple columnar epithelium
is the muscularis externa thicker or thinner compared to other regions of the alimentary canal?
thicker
what type of muscle comprises the external anal sphincter?
skeletal muscle
how does the epithelium change in the anal canal?
from simple columnar to stratified squamous
what absorption takes place in the colon?
active transport of sodium into the blood leads to the osmotic absorption of water
what can long residence time in the colon lead to?
bacterial colonisation
how much colonic microflora is there in the human gut?
1kg
what does bacterial fermentation of undigested carbohydrate lead to?
> short chain fatty acids
vitamin k
gas
name the gases produced in the colon
> nitrogen > methane > co2 > hydrogen > hydrogen sulphide
describe the events in the rectum following a meal
> mass movement contraction from colon to rectum = distension of faecal material into rectum
mechanoreceptors triggered
defaecation reflex stimulated
creates urge to defecate
what is the nerve innervation of the defaecation reflex?
parasympathetic control via pelvic splanchnic nerves
describe the defaecation reflex
> contraction of rectum
relaxation of internal sphincter
contraction of external sphincters
increased peristaltic activity in colon
what symptoms are associated with constipation?
> headaches
nausea
loss of appetite
abdominal distension
what can cause diarrhoea?
> pathogenic bacteria > protozoans > viruses > toxins > food > stress
what are the effects of protein enterotoxins produced by enterotoxigenic bacteria?
the maximally turn on intestinal chloride secretion from crypt cells creating an increase in h2o secretion
how to protein enterotoxins turn on intestinal chloride secretion?
They elevate intracellular secondary messengers:
> cAMP
> cGMP
> calcium
why does increased h2o secretion create watery diarrhoea?
it swamps the absorptive capacity of villus cells
what is the treatment for enterotoxins?
oral rehydration therapy: sodium glucose solution
how does sodium/glucose solution help treat diarrhoea?
it drives h2o absorption allowing for rehydration, and since secretion is ongoing the infection is washed away.
