Large intestine structure and function Flashcards
How long is the large intestine?
1.5-1.8m
What are the 4 parts of the large intestine?
Ascending
Transverse
Descending
Sigmoid
What are the muscle layers of the large intestine?
Complete circular muscle layer
Incompletele longitudinal muscle layer
What are taenia coli?
3 bands of longitudinal smooth muscle spinning the entire length of the colon
What is the composition of the epithelium?
Simple columnar epithelium containing large straight crypts with large numbers of goblet cells
What is the function of crypts in the large intestine?
Allows for lubrication for movement of faeces
What is the structure of the rectum?
Straight muscular tube with a simple columnar epithelium mucosa and thick muscular extrana
What is the structure of the anal canal?
Stratified squamous epithelium
Very thick muscular externa
2-3cm long
What is the function of the large intestine?
Actively transport Na into the blood, causing absorption of water , leading to dehydration of chyme and solid faecal pellets
What does the long residence time in the colon cause?
Bacterial colonisation
How much bacteria is in the colon at any given point?
1kg
Whathappens to undigested carbohydrates in the colon?
Bacterial fermentation to short chain fatty acids
What are the products of bacterial fermentation of carbohydrates in the colon?
Short chain fatty acids
Vit K
Gases- N, CO2, H, methane, hydrogen sulphide
What normally closes the anus?
Internal and external anal sphincters?
What types of muscle are present in the anal sphincters?
Internal= smooth External= skeletal
What happens in the rectum following a meal?
Wave of mass movement contraction in the colon that spreads to the rectum
Mass of faecal material is moved to rectum, causing distension
The mass activates mechanoreceptors, activating the defection reflex
What is the defection reflex?
“urge to go”
Parasympathetic control via the pelvic splanchnic nerves
Initiates contraction of rectum, relaxation of internal and contraction external anal sphincters
Increased peristaltic activity in the colon
What are the symptoms of constipation?
Headaches
Nausea
Loss of appetite
Abdominal distension
What is the cause of constipation?
Distension of the rectum
What is diarrhoea?
Too frequent passage of faeces which are too liquid
What are the causes of diarrhoea?
Pathogenic bacteria Protozoans Viruses Toxins Food Nervousness
What are enterotoxigenic bacteria?
Bacteria which produce protein enterotoxins
What do enterotoxins do in the colon?
Turn on maximum intestinal chloride secretion from crypt cells, causing increases H2O secretion
How to enterotoxins act?
By activating intracellular second messengers e.g. cAMP, cGMP and Ca
What is the treatment for diarrhoea?
Na and glucose solutions to drive H2O reabsorption
Oral rehydration therapy
