Physiology Of Defecation

Question 1

Functions of the colon

Answer 1

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

Question 2

Normal colonic transit time

Answer 2

24-48 hours

Question 3

Length of colon in an adult

Answer 3

1.5m

Question 4

What controls passage of stool into caecum from ileum

Answer 4

Ileocaecal valve

Question 5

Parts of colon

Answer 5

Caecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon

Question 6

What is the name of the bend between ascending and transverse colon

Answer 6

Hepatic flexure

Question 7

Where does majority of absorption of water and electrolytes occur

Answer 7

Ascending colon
First part of transverse colon

Question 8

What is the name of the bend between transverse and descending colon

Answer 8

Splenic flexure

Question 9

Layers of the colonic wall

Answer 9

Mucosa
Muscularis mucosae
Submucosa
Muscularis propria
Subserosa
Serosa

Question 10

histology of colonic mucosa

Answer 10

Single layer of columnar epithelium
Goblet cells
Lamina propria- inflammatory cells

Question 11

Muscularis propria of colon

Answer 11

Inner circular muscle (CM)
Auerbach nerve plexus
Longitudinal muscle (LM)

Question 12

Function of longitudinal muscle in colon muscularis propria

Answer 12

Segmental motility

Question 13

Function of inner circular muscle in colon muscularis propria

Answer 13

Mass movement by peristalsis

Question 14

Which nerve plexus is in the muscularis propria of the colon

Answer 14

Auerbach nerve plexus

Question 15

Haustra

Answer 15

saccules in the colon that give it its segmented appearance. Haustral contraction is activated by the presence of chyme and serves to move food slowly to the next haustra, along with mixing the chyme to help with water absorption

Question 16

Taenia coli

Answer 16

three bands of longitudinal smooth muscle on the colon surface

Question 17

What produces Haustra

Answer 17

Longitudinal muscle

Question 18

Nerve supply to colon

Answer 18

Enteric nervous system
Intrinsic
Extrinsic

Question 19

What are receptors in colon (entry of faeces)

Answer 19

Mucosal stretch receptors

Question 20

Extrinsic nervous system

Answer 20

Parasympathetic
Sympathetic

Question 21

Intrinsic nervous system of colon

Answer 21

Myenteric plexus
Submucosal plexus

Question 22

Which nerve controls defecation

Answer 22

Pelvic nerve

Question 23

What stimulates defecation reflex

Answer 23

Parasympathetic stimulation

Question 24

Parts of anal sphincter

Answer 24

Internal hemorrhoid tissue
Levator ani muscle
Internal anal sphincter
External anal sphincter
External hemorrhoid tissue

Question 25

Pudendal nerve

Answer 25

Somatic Controls external anal sphincter to maintain continence

Question 26

4 phases of defecation

Answer 26

Basal Pre-expulsive Expulsive Termination

Question 27

External anal sphincter

Answer 27

Circular striated muscle

Question 28

Internal anal sphincter

Answer 28

Smooth muscle

Question 29

Levator ani muscle

Answer 29

Support anal-rectum Part of pelvic floor

Question 30

Puborectalis muscle

Answer 30

When contracted promotes continence 90 degree angle- bending analysis pathway

Question 31

Basal phase of defecation

Answer 31

Colon- segmental contractions (mixing) Rectum - motor complexes (to keep rectum empty) Anal sphincter- tonic contraction Puborectalis- contracted (90 degree anorectal angle)

Question 32

Anorectal angle to maintain continence

Answer 32

90 degrees

Question 33

Pre-expulsive phase of defecation

Answer 33

Colon- high amplitude propagating contractions -mass movement of stool 8 times a day -gastro-colic reflex Rectum- fills causing distension -rectal compliance Anal sphincter- EAS maintains contraction -reflex relaxation of IAS (RAIR)- for stool sampling Puborectalis- remains contracted

Question 34

Mass movement of stool per day

Answer 34

8 times

Question 35

Stool sampling

Answer 35

Reflex relaxation of internal anal sphincter External anal sphincter maintains contraction Tests whether stool is solid, liquid, gas

Question 36

Constipation

Answer 36

Condition where go to toilet less than 3 times a week

Question 37

Expulsive phase of defecation

Answer 37

Rectum contracts IAS, EAS and PR relaxes Valsalva manoeuvre/posture aid emptying

Question 38

Sitting posture while defecating

Answer 38

Puborectalis muscles chokes rectum to maintain continence

Question 39

Squatting posture when defecating

Answer 39

Puborectalis muscle relaxes and straightens pathway to anus

Question 40

Termination phase of defecation

Answer 40

Traction loss causes sudden contraction of EAS ( closing reflex) Valsalva ceases Change in posture to standing

Question 41

Disorders of defecation - constipation/obstructive defecation

Answer 41

Consistency of stool Bowel motility Physical blockage to the bowel Pelvic floor disorders

Question 42

Diagnostic testing for constipation/obstructive defecation

Answer 42

Colonic transit study Defecating proctogram Anorectal manometry

Question 43

Disorders of defecation - faecal incontinence

Answer 43

Consistency of stool or frequency of movements Diseased bowel mucosa Reduced rectal capacity Pelvic floor disorder

Question 44

Diagnostic testing for faecal incontinence

Answer 44

Endo-anal ultrasound Anorectal manometry

Question 45

Anorectal manometry

Answer 45

Measures pressure generated by contraction of muscles