Physiology of Defecation

Question 1

What are the 3 functions of the Colon?

Answer 1

1) Production of vitamins
2) Excretion of waste
3) Absorption of water and electrolytes

Question 2

Describe the layers of the colonic wall

Answer 2

Mucosa –> MM –> SM –> MP –> SubS –> S

Question 3

What structure is made of 3 ‘stripes’ of longitudinal muscle?

Answer 3

Taeniae Coli

Question 4

What is the name for bits ‘hanging off’ the colon?

Answer 4

Epiploicae Appendices

Question 5

Describe the epithelium of the Colon

Answer 5

1) Columnar Epithelium

2) Goblet Cells: Mucous for lubrication

Question 6

How is water and electrolytes absorbed in colon?

Answer 6

W: By osmosis
E: Active Transport

Question 7

How are vitamins of the colon produced?

Answer 7

Colonic microbiome break down indigestible fibres to produce vitamin K and B

Question 8

Describe extrinsic nerve supply to colon

Answer 8

Parasympathetic: Vagus Nerve
Sympathetic: Thoracic (Lesser and Least)

Question 9

Describe Intrinsic nerve supply to colon

Answer 9

1) Meissner’s Plexus (Submucosa)

2) Auerbach’s (Muscularis externa between circular and longitudinal layers)

Question 10

Describe structure of anal sphincter

Answer 10

Rectum –> Anus
Muscles: Internal and External Anal Sphincter
(Levator Ani muscle, and Pelvic floor)

Question 11

What happens (Muscularly) when rectum is empty?

Answer 11

Both sphincters and puborectalis are contracted

Question 12

How is defaecation carried out? (3)

Answer 12

1) External sphincter and puborectalis relax
2) Rectum contract
3) Valsalva manoeuvre

Question 13

How can diarrhoea be discovered?

Answer 13

By either the consistency of stool or frequency of movements