Physiology of colon and appendix, rectum and anus

Question 1

Explain the 3 parts of the large intestine

Answer 1

1 - Caecum: Junction with small intestine that starts at ileo-caecal valve
2 - The colon: Acending, transverse, descending
3 - Rectum: Continues as anal canal and opening as anus

Question 2

What is the function of the large intestine

Answer 2

Recieves and stores material from small intestine

Absorbs water and salts

B-complex vitamins are produced by large intestine bacteria

Question 3

What are the functions of bacteria in the large intestine

Answer 3

• Metabolsim: Digests non-digestible CHO
• Morphological function: Increase mucus, reduce cell permeability, Increase vascular flow, increase tissue repair
• Immune: influence maturation and development of lymphoid tissue, increases IgA
• Nervous system: Influence synaptic connectivity
• Bone homeostasis function: Increase uptake of calcium

Question 4

What is meant by gastrocolic/duodenocolic reflexes

Answer 4

It is the initiation of peristalsis in the large intestine by the stomach or duodenum

Question 5

Which factors control contractile activity of colon

Answer 5

1. Intrinsic smooth muscle properties
2. Intrinsic nerves
3. Extrinsic nerves
4. Circulating/local chemicals

Question 6

What are the transit times of the large intestine

Answer 6

Caecum: 4 hours
Hepatic flexure: 6 hours
Splenic flexure: 9 hours
Pelvic colon: 12 hours

Question 7

Explain the process of defaecation

Answer 7

When faeces enters the rectum the rectum distends causing the initiation of signals. These signals spread over myenteric plexus to cause peristaltic waves in descending colon, sigmoid and rectum. This results in faeces being propelled to the anus and the internal sphincter relaxing.
When volutarily controlled external sphincter also relaxes and defaecation occurs

Question 8

What are the other responses that also occur during defaecation

Answer 8

Deep inspiration
Fixation of diaphragm
Contraction of abdomen and chest wall
Closure of epiglottis

This increases intraabdominal pressure which assists in expulsion

Question 9

What are the contests of faeces

Answer 9

Inorganic material
Bile pigements
Undigested plant fibres
Bacteria
Water

Question 10

When is constipation classified and what are possible causes

Answer 10

Bowel movement occurs every 2-3 days or up to 3 times a day

Less than 3 times per week is constipation

Causes:
- Prolonged inhibition of defaecation relfex
- Lack of tone in smooth muscle fibres of colon and spasms of large intestine muscle layer
- Slight anorexia

Question 11

What is diarrhoea and what are possible causes

Answer 11

Its when faeces moves faster than usual through the colon and remains liquid

Causes:
- Hypersecretion of fluids
- Abnormally frequent peristaltic waves: emotional stress, chemicals, infection

Question 12

What is the appendix

Answer 12

It is an extension of the bowel and is a narrow pouch of tissue made up of lymphoid tissue in the submucosa

It is a remnant of the caecum to digest cellulose or storgae area for beneficial bacteria