Large Intestine - Structure and Function Flashcards
What are the 4 parts of the large intestine?
Ascending
Transverse
Descending
Sigmoid
What are the bands in the large intestine called and how many are there?
Teniae coli
3 that run along the entire length of colon
What does contraction of teniae coli do?
Forms haustra (pouches)
What is the mucosa layer of the large intestine made of?
Simple columnar epithelium - flat
What are the crypts in the large intestine like?
Large, straight with a lot of goblet cells so there is plenty lubrication for the movement of faeces
What is the mucosa of the rectum made of?
Simple columnar epithelium
How does the muscularis externa in the rectum differ from the rest of the alimentary canal?
Thicker
What is the rectum?
Straight, muscular tube between the sigmoid colon and the anal canal
Where is the anal canal?
2-3cm between distal rectum and anus
How does the muscularis externa of the anal canal differ from the rectum?
Thicker than the rectum because of the internal anal sphincter
What is the external anal sphincter made of?
Skeletal muscle
How does the epithelium change in the anal canal?
Simple columnar -> stratified squamous
What is the role of the colon in absorption?
No nutrient absorption
Actively transports Na from lumen to blood = absorption of water = dehydration of chyme = solid faecal pellets
What is the role of microflora in the colon?
Supplies vitamin K
How is the anus kept closed?
By internal anal sphincter (smooth muscle under automatic control) and external anal sphincter (skeletal muscle under voluntary control)
What happens following a meal to lead towards defaecation?
Wave of intense contraction (MMC) moves through the colon to the rectum
Distension of the rectal wall is produced by mass movement of faecal material into rectum which is picked up by mechanoreceptors leading to defaecation reflex
How is the defaecation reflex controlled?
Under parasympathetic control via pelvic splanchnic nerves
NO sympathetic influence
What makes up the defaecation reflex?
Contraction of rectum
Relaxation of internal anal sphincter
Contraction of external anal sphincter
Increased peristaltic activity in colon - causes increased pressure on external anal sphincter = relaxes it
What happens in constipation?
No absorption of toxins from faecal material following long periods of retention
What are the symptoms associated with constipation?
Headaches
Nausea
Loss of appetite
Abdominal distension
What is diarrhoea?
Too frequent passage of faeces which are too liquid
What are the causes of diarrhoea?
Pathogenic bacteria Protozoans Viruses Toxins Food Stress
What does enterotoxigenic bacteria do?
Produces protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells causing an increase in water secretion
How does enterotoxins increase Cl secretion and hence water secretion?
Elevate intracellular second messengers:
cAMP
cGMP
calcium
How is secretory diarrhoea treated?
Sodium/glucose solution which drives water absorption = rehydration
