Physiology of the large intestine

Question 1

what are the bulges in the LI called?

Answer 1

Haustra

Question 2

what type of digestion occurs in the LI and how?

Answer 2

Mechanical - chyme enters through ileocaecal valve, haustral churning, peristalsis is slow because we want to compact and concentrate the contents

Chemical (very limited) - only bacterial enzymes present, ferment remaining carbohydrates to produce flatus and break down remaining amino acids

Question 3

what stimulates colonic movement ?

Answer 3

morning awakening

Question 4

what does the gastrocolic reflex cause?

Answer 4

increase motility in colon in response to stretch in the stomach and byproducts of digestion in SI

Question 5

what does faeces contain?

Answer 5

undigested food
inorganic salts
sloughed off epithelial cells
bacterial products
bacteria

Question 6

What is the colonic environment in each section?

Answer 6

Ascending - relatively fluid
Transverse - less water some gas
Descending - risk of impaction (too concentrated) more solid

Question 7

what is the process of defaecation ?

Answer 7

reflex initiated by distension of rectum (parasympathetic input to open internal anal sphincter - involuntary)

This causing increased pressure in the rectum causing the longitudinal muscle to shorten

Voluntary contraction of diaphragm and abdomen (skeletal muscle)

External anal sphincter opens