Defeacation

Question 1

Functions of the colon? [3]

Answer 1

Absorption of water and electrolytes (osmosis)
Excretion of waste (motility)
Production if vitamins/regulation of immune system (microbiome)

Question 2

Where does most of the absorption of water and electrolytes take place?

Answer 2

Ascending colon and first half of transverse colon.

Question 3

Layers of the colonic wall?

Answer 3

mucosa
muscularis muscosa
submucosa
muscularis propria
subserosa
serosa

Question 4

Describe the colonic mucosa?

Answer 4

single layer columnar epithelium - microvilli
goblet cells
lamina propria - inflammatory cells

Question 5

Describe histology of the muscularis propria of the colon

Answer 5

inner circular muscle - mass movement by peristalsis
longitudinal muscle - segmental mobility

between the two is Auerbach nervus plexus

Question 5

Describe the nervous supply of the colon

Answer 5

intrinsic - myenteric plexus (Auerbach’s) , submucosal plexus (absorption of contents)
extrinsic - parasympathetic and sympathetic
Anorectum - pelvic nerve

Question 5

How does defecation rely of the nervous system?

Answer 5

Stretching of the wall activates mucosal stretch receptors
Afferent nerve send signals to spinal cord to the brain
Signals sent to descending colon via pelvic nerve afferents
As it fills, mechanic receptors will be activated when ready

Question 6

Which nerve controls voluntary defecation?

Answer 6

pudenal nerve

Question 7

What are the two anal sphincters?

Answer 7

Internal - involuntary

External - striated muscle - voluntary

Question 8

Puborectalis muscle

Answer 8

at rest, creates 90’’ angle between rectum and anal canal - promotes continence -
part of the li

Question 9

What are the 4 phases of defecation?

Answer 9

basal phase
pre-expulsive
expulsive
termination

Question 10

What occurs during basal phase?

Answer 10

segmental contractions of the colon
motor complexes in the rectum keep rectum empty
anal sphincter - tonic contraction
puborectalis - conttracted for 90’ anorectal angle

Question 11

What occurs during pre-expulsive phase?

Answer 11

High amplitude propagating contractions in the colon
Mass movements, gastro-colic reflex

rectum - fills, causing distension
- rectal compliance (adaptive relaxation)

anal sphincter - external one maintains contraction
reflex relaxation of internal for stool sampling
Puborectalis remains contracted

Question 12

What are mass movements?

Answer 12

When food moves out of the stomach ~ 8 times a day

Question 13

What happens during the expulsive phase?

Answer 13

rectum contracts
internal, external and pubarectalis relax
valsalva manouvre/posture facilitates emptying

Question 14

Termination phase

Answer 14

Traction loss causes sudden contraction of eas (closing reflex)
valsalva ceases
change in posture to standing

Question 15

What is constipation?

Answer 15

Someone goes to the toilet less than 3 times a week - often multifactoral

Question 16

What can contribute to constipation?

Answer 16

consistency of stool - too solid to pass
bowel motility - slow bowel
physical blockage to the bowel - rare
pelvic floor disorders - difficulty emptying

Question 17

Colonic transit study?

Answer 17

Swallow 3 capsules
MArkers with BaSO4
Should mostly be gone
If still there and dispersed throughout colon, can be sign of slow transit colon

Question 18

Anorectal manometry

Answer 18

tests function of anal sphincter

Question 19

What is fecal incontinence?

Answer 19

Involuntary passage of stool - mostly multifactorial

Question 20

What can cause fecal incontinence?

Answer 20

consistency of stool - can be affected by diet
frequency of movements
diseased bowel mucosa
reduced rectal capacity
pelvic floor disorder

Question 21

What can be used to test for fecal incontinence?

Answer 21

endo-anal ultrasound - looks at sphincter thickness and completeness
anorectal manometry - sphincter pressure