Large Intestine Structure and Function Flashcards
What is the sphincter between the ileum and the caecum?
Ileocecal valve
What are the 4 parts of the colon?
Ascending
Transverse
Descending
Sigmoid
Describe the muscularis externa of the large intestine?
Circular muscle layer complete but longitudinal muscle layer incomplete
What are the 3 bands of longitudinal muscle layer called?
Teniae coli - extends the whole length of colon
What does contractions of teniae coli cause?
Pouches called haustra - puckered appearance
Describe the mucosa of the large intestine
Simple columnar epithelium - flat
Large straight crypts lined with goblet cells
What is the function of goblet cells on the crypts?
Secrete mucus which lubricates the movement of faeces
Describe the histology of the rectum?
Muscular tube
Simple columnar epithelium
Thick muscularis externa
Describe the histology of the anal canal
Muscualris thicker than rectum
Simple columnar but moves to stratified squamous outside body
What is the difference between the internal and external anal sphincter?
Internal - smooth muscle
External - skeletal muscle so under voluntary control
Describe the function of the colon
No important nutrient absorption role
Actively transports Na from lumen into blood so osmotic absorption of water which dehydrates chyme - solid faeces
What does the long residual time in colon cause?
Bacterial colonisation (helps break down cellulose)
Bacterial fermentation of undigested carbohydrate
What are the products of bacterial fermentation of undigested carbohydrate?
Short chain fatty acids
Vitamin K - blood clotting
Gas - nitrogen, CO2, hydrogen, methane, hydrogen sulphide
Describe defaecation following a meal
Wave of intense contraction (MMC) from colon to rectum
Distention of rectal wall activates mechanoreceptors causing defaecation reflex
What nerve system controls the defaecation reflex?
Under parasympathetic control by pelvic splanchnic nerve
(no sympathetic control)
Describe the defaecation reflex
Contraction of rectum
Relaxation of internal and contraction external anal sphincters
Increased peristaltic activity in colon
What does increased pressure on external anal sphincter cause?
Relaxation under voluntary control so them expulsion of faeces
What causes a delay in defaecation?
Descending pathways
What are some symptoms with constipation?
Headaches
Nausea
Loss of appetite
Abdominal distention - due to distention of rectum
Does constipation effect absorption of faecal material?
No absorption of toxins
What is diarrhoea?
Too frequent passage of faeces which are too liquid
What are some causes of diarrhoea?
Pathogenic bacteria
Protozoans
Viruses
Toxin
Food
What are examples of enterotoxigenic bacteria?
Vibrio cholerae
E.coli
Describe enterotoxigenic bacteria
Produce protein enterotoxins which maximally turn on intestinal Cl secretion from crypt cells which increases water secretion
What intracellular messengers does enterotoxins elevate?
cAMP - activates CFTR
cGMP
Calcium
How does water secretion effect villus cells?
Swamps absorptive capacity of villus cells so perfuse watery diarrhoea
Do enterotoxins damage villus cells?
No
What is the treatment of secretory diarrhoea?
Give sodium/ glucose solution
How does sodium/glucose solution help secretory diarrhoea?
Drives H2O absorption so rehydrates
Secretion still going so washes away infection
What is the treatment to secretory diarrhoea called?
ORS - oral rehydration therapy
