Large Intestine Structure and Function Flashcards
Name the valve between the small intestine and large.
Iliocaecal valve
What is the role of the ileocecal valve?
Controls entry of food into large intestine and closes to prevent backflow
Why is it important that there is no backflow once food has entered the large intestine?
Large intestine contains a lot more bacteria
What is the name of the first part of the large intestine?
Caecum
Which structure is attached to the caecum?
Appendix
How long is the large intesine?
Approx. 1.5-1.8m
After the caecum, list the remaining parts of the large intestine in the order they would be.
Caecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Describe the muscle layers of the large intestine
Similarly to the small intestine, it has a circular and longitudal muscle layer.
However, the circular layer is competed, the longitudal layer is incomplete.
This means longitudal muscle does not fully encircle the diameter of the large intestine
What is the name of the three bands which span the length of the colon?
Teniae coli
What is responsible for the puckered appearance of the large intestine?
Haustra (pouches) formed by incomplete longitudal muscle
What are in the crypts of the large intestine?
Goblet cells
What do the goblet cells in the large intestine produce and why is this required?
Mucous, lubrication for movement of faeces
What comes after the sigmoid colon?
Rectum
What is the rectum?
Straight muscular tube connecting sigmoid colon and anal canal
What is the mucosa of the rectum composed of?
Simple columnar epithelium
Why is the muscularis externa of the rectum thicker than other areas of the GIT?
Important to have strong muscles to hold the faeces in
What is the anal canal?
Short distance between rectum and anus
What is the name of the thickened muscle (thicker than rectum) in the anal canal?
Internal Anal Sphincter
Is the Internal Anal Sphincter voluntary or involuntary?
Involuntary
What type of muscle is the Internal Anal Sphincter composed of?
Smooth muscle
What is the Internal Anal Sphincter controlled by?
Autonomic NS
What type of muscle is the External Anal Sphincter composed of?
Skeletal
Is the External Anal Sphincter voluntary or involuntary?
Voluntary
What type of epithelium is in the anal canal?
Stratified squamous
What are the three parts of the GIT with stratified squamous peithelium?
Mouth
Oesophagus
Anal canal
What is the main function of the colon?
Actively transport sodium from the lumen to the blood to help with the absorption of water and dehydration of chym
What happens to the chyme in the colon because it stays there for a longer period of time?
Bacterial colonisation
How much weight of an adult human is composed of bacteria?
1kg
What can happen to undigested carbohydrate in the colon?
Bacterial fermentaion
Which vitamin can the bacteria in the colon help with forming?
Vitamin K
What do we need vitamin K for?
Clotting of blood
Was it formed in the colon as a result of the bacterial fermentaion?
Gas- nitrogen, hydrogen, CO2, methane, hydrogen sulphide
Describe how defaecation work following a meal.
-External and internal anal sphincters usually closed.
-After a meal, wave of intense contraction moving food from the colon to the rectum.
-Mechanoreceptors provide defaecation reflex meaning there is an urge to defaecate
What is the defaecation reflex controlled by?
Parasympathetic NS via pelvic splenic nerves
What happens after contraction of the rectum?
Relaxation of internal and external anal sphincters
What pushes the faeces out of the body?
Increased peristaltic activity in colon
What happens if you don’t want to take a poo right then?
Increased pressure on external and internal anal sphincters until we get to a toilet
How is constipation different for different people?
Different people have a poo different amounts. For example, some people go once or multiple times a day, some only go once every three days.
Constipation means going less frequently than is normal for you- for example, if someone goes once a day and hasn’t been for a few days.
What are some symptoms associated with constipation?
Headaches
Nausea
Loss of appetite
Abdominal discomfort
Is there any reabsorption of toxins if faeces is retained for long periods of time?
No
What are some of the lifestyle management of constipation?
Drinking plenty
Lots of fibre
More exercise
What is diarrhoea?
Too frequent passing of faeces which are too liquid
What are some of the causes of diarrhoea?
Pathogenic bacteria
Protozoans
Viruses
Toxins
Food
Stress
What is the most common cause of death for children <5 in developing countries?
Diarrhoea
What happens when we have movement of chlorine from the basolateral membrane to the lumen of the large intestine?
(same as w small intestine and the CFTR transporter of chlorine!)
Helps movement of water into the lumen
What happens if there is an issue with the CFTR transporter and more and more chlorine is getting into the lumen of the colon?
More water will also come in causing watery faeces
What is meant by enterotoxigenic bacteria?
Bacteria which secrete toxins
Give an example of an enterotoxigenic bacteria which increases the release of water and chlorine.
Vibrio cholerae
How do enterotoxigenic bacteria increase water secretion?1
Elevating intracellular second messengers like cAMP, calcium or cGMP which increases the secretion of water
How much water is usually produced by the small intestine in a day?
1.5L
What can the bacteria Vibrio cholerae cause?
Cholera
How much water can the small intestine produce when infected by Vibrio Cholerae?
25L
As well as loss of water in diarrhoea, what else can happen?
Loss of water = dehydration
Loss of minerals
What is the treatment of secretory diarrhoea?
Hydration therapy- sodium/glucose solution
Do enterotoxins damage villi cells?
No so they can keep absorbing water
Why is a sodium/glucose solution used in hydration therapy?
Drives water absorption causing rehydration
If there is severe infection caused by diarrhoea, which other treatment may be required?
Antibiotics
