Large intestine structure and function

Question 1

How long is the large intestine?

Answer 1

1.5-1.8m

Question 2

What are the 4 parts of the large intestine?

Answer 2

Ascending
Transverse
Descending
Sigmoid

Question 3

What are the muscle layers of the large intestine?

Answer 3

Complete circular muscle layer

Incompletele longitudinal muscle layer

Question 4

What are taenia coli?

Answer 4

3 bands of longitudinal smooth muscle spinning the entire length of the colon

Question 5

What is the composition of the epithelium?

Answer 5

Simple columnar epithelium containing large straight crypts with large numbers of goblet cells

Question 6

What is the function of crypts in the large intestine?

Answer 6

Allows for lubrication for movement of faeces

Question 7

What is the structure of the rectum?

Answer 7

Straight muscular tube with a simple columnar epithelium mucosa and thick muscular extrana

Question 8

What is the structure of the anal canal?

Answer 8

Stratified squamous epithelium
Very thick muscular externa
2-3cm long

Question 9

What is the function of the large intestine?

Answer 9

Actively transport Na into the blood, causing absorption of water , leading to dehydration of chyme and solid faecal pellets

Question 10

What does the long residence time in the colon cause?

Answer 10

Bacterial colonisation

Question 11

How much bacteria is in the colon at any given point?

Answer 11

1kg

Question 12

Whathappens to undigested carbohydrates in the colon?

Answer 12

Bacterial fermentation to short chain fatty acids

Question 13

What are the products of bacterial fermentation of carbohydrates in the colon?

Answer 13

Short chain fatty acids
Vit K
Gases- N, CO2, H, methane, hydrogen sulphide

Question 14

What normally closes the anus?

Answer 14

Internal and external anal sphincters?

Question 15

What types of muscle are present in the anal sphincters?

Answer 15

Internal= smooth
External= skeletal

Question 16

What happens in the rectum following a meal?

Answer 16

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

Question 17

What is the defection reflex?

Answer 17

“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

Question 18

What are the symptoms of constipation?

Answer 18

Headaches
Nausea
Loss of appetite
Abdominal distension

Question 19

What is the cause of constipation?

Answer 19

Distension of the rectum

Question 20

What is diarrhoea?

Answer 20

Too frequent passage of faeces which are too liquid

Question 21

What are the causes of diarrhoea?

Answer 21

Pathogenic bacteria
Protozoans
Viruses
Toxins
Food
Nervousness

Question 22

What are enterotoxigenic bacteria?

Answer 22

Bacteria which produce protein enterotoxins

Question 23

What do enterotoxins do in the colon?

Answer 23

Turn on maximum intestinal chloride secretion from crypt cells, causing increases H2O secretion

Question 24

How to enterotoxins act?

Answer 24

By activating intracellular second messengers e.g. cAMP, cGMP and Ca

Question 25

What is the treatment for diarrhoea?

Answer 25

Na and glucose solutions to drive H2O reabsorption

Oral rehydration therapy