Large Intestine Structure and Function

Question 1

Where does the ileum finish and the caecum begin?

Answer 1

The ileocaecal valve

Question 2

What is the caecum?

Answer 2

The first part of the colon/ large intestine

Question 3

Why is the caecum described as a blind sac?

Answer 3

Caecum means blind in latin, named because it has no function in humans

Question 4

What two structures enter the caecum?

Answer 4

The ileocaval valve and vermiform appendix

Question 5

What regions of the colon are there?

Answer 5

Ascending, transverse, descending and sigmoid

Question 6

What layers of the muscluaris externa are there in the large intestine?

Answer 6

Circular muscles and longitudinal muscles

Question 7

Which layer of the muscularis externa is incomplete?

Answer 7

Longitudinal

Question 8

What muscles lead to puckered appearance of the large intestine?

Answer 8

Contraction of the teniae coli (run entire length of colon)

Question 9

Describe the histology of the large intestine mucosa?

Answer 9

Mucosa comprised of simple columnar epithelium

Large straight crypts lined with large numbers of goblet cells for lubrication and movement of faeces

Question 10

Describe the rectum?

Answer 10

Straight muscular tube between end of sigmoid colon and anal pit

Question 11

What is the difference between the rectal muscular externa and other regions of the canal?

Answer 11

Thick compared to other regions of the canal

Question 12

What is the anal canal?

Answer 12

2-3cm between the distal rectum and anus

Question 13

Describe the type of muscles in the anal sphincters

Answer 13

Internal - smooth muscle

External - skeletal muscle

Question 14

What is the osmotic role of the colon?

Answer 14

Dehydrates chyme and creates faecal pellets

Question 15

What benefit is three to a long residence time within the large intestine?

Answer 15

Leads to bacterial colonisation which allows fermentation of undigestible carbohydrates to yield short chain fatty acids and vitamin K

Question 16

Describe the anal sphincters at rest

Answer 16

Closed

Question 17

What is a mass movement contraction?

Answer 17

Distention of rectal wall produced stimulates mechanoreceptors which lead to the defection relaxation

Question 18

What nerve is responsible for the defecation relaxation?

Answer 18

Pelvic splanchnic nerve (parasympathetic)

Question 19

What are enterotoxigenic bacteria?

Answer 19

Bacteria which produce enterotoxins - maximally turn on intestinal chloride secretion, causing profuse watery diarrhoea

Question 20

How do enterotoxigenic bacteria stimulate chloride channels?

Answer 20

Act by elevating intracellular secondary messengers like cAMP cGMP and calcium

Question 21

What is the treatment for secretory diarrhoea?

Answer 21

Give sodium/glucose solution to drive H2O absorption

Question 22

What treatment method saves 2 million children lives per year for diarrhoea?

Answer 22

Oral rehydration therapy