What valve is between the ileum and the caecum?
What is the length of the colon?
Ranges from 1.5 to 1.8m
What are the 4 parts of the large intestine?
Explain how the circular and longitudinal muscles of the colon are different from the small intestine?
Circular muscle is complete but the longitudinal is not
What are the three bands present along the entire length of the colon?
What are tenaei coli?
Three seperate longitudinal ribbons of smooth muscle running through the entire colon
What are the pouches present throughout the colon called?
What produces haustra?
Contractions of the teniae coli
What is the classification of the mucosa in the colon?
Simple columnar epithelium that is flat
What is contained in the crypts within the colon?
Why are goblet cells present in the colon?
Secrete mucous that is used as lubrication for faeces to move
What is the rectum?
Straight, muscular tube between the end of sigmoid colon and anal canal
What is the classification of the mucosa of the rectum?
Simple columnar epithelium
How does the muscularis externa of the rectum compare to other regions of the alimentary canal?
It is thicker
What is the anal canal?
2-3cm between distal rectum and anus
How does the muscularis externa of the anal canal compare to the rectum?
Is thicker forming the internal anal sphincter
What is the internal anal sphincter formed from?
Muscularis externa (smooth muscle)
What is the external anal sphincter formed from?
How does the epithelium change in the anal canal?
Changes from simple columnar to stratified squamous
Does the colon have an important nutrient absorpion role?
Not in humans
What is the function of the colon?
Actively transport sodium from lumen into the blood, causing osmotic absorption of water
This causes dehydration of chyme causing solid faecal pellets
What cause faeces to be solid?
Water is absorbed, causing dehydration of faeces, due to the colon transporting sodium from the lumen to the blood creating an osmotic difference
What causes bacterial colonisation of the colon?
Large residence time
How much bacteria is present in the colonc microflora?
1014 (about 1kg)
What happens to undigested carbohydrates in colon?
What are consequences of bacterial colonisation of the colon?
Bacterial fermentation of undigested carbohydrates, short chain fatty acids and vitamin K
Production of gas
Why does defaecation not occur passively?
Anus is closed by internal anal sphincter (smooth muscle under autonomic control) and external anal sphincter (skeletal muscle under voluntary control)
Explain the mechanism that occurs following a meal that leads to defaecation?
1) Wave of intense contraction (mass movement contraction) from the colon into the rectum
2) Distension of rectal wall produced by mass movement of faecal material into rectum
3) Activated mechanoreceptors activate the defaecation reflex
4) Causes urge to defaecate
What controls the defaecation reflex?
Parasympathetic nervous system (via pelvic splanchnic nerves) with no sympathetic influence
How can defaecation be voluntary delayed?
By descending neural pathways