Colonic Motility and Defacation

Question 1

What are two histological features of the colom?

Answer 1

Folds - outer longitudinal muscle, arrangement of mucosa highly adapted to its function
Colonic crypts - absorption

Question 2

What does the colon absorb?

Answer 2

Water and electrolytes (Na+)

Question 3

What does the colon secrete?

Answer 3

Mucous, Cl-

Question 4

What are the absorptive cells of the colon?

Answer 4

Colonocytes

Question 5

What is the boundary between the large and small intestine called?

Answer 5

Ileo caecal junction - high pressure zone

Question 6

How is tone increased and decreased?

Answer 6

Increased by sympathetic nerve supply
Decreased by gastrin

Question 7

What does the high pressure zone respond to?

Answer 7

Both ileal and colonic distension

Question 8

What is the function of the ileocaecal valve?

Answer 8

Prevents backflow of material (bacteria) into small intestine

Question 9

What is valve opening controlled by?

Answer 9

Both small and large intestine - facilitates unidirectional movement

Question 10

What is the function of the ascending colon?

Answer 10

Half of the chyme is cleared within 90 mins

Question 11

What is the function of the transverse colon?

Answer 11

Removal of water and electrolytes
Material retained for ~24 hrs

Question 12

What is the function of the descending colon?

Answer 12

Storage of material

Question 13

What is the function of the recto-sigmoid region?

Answer 13

Reservoirs for faeces
36-48 hrs

Question 14

What are taenia coli?

Answer 14

Aggregation of longitudinal muscle into 3 bands resulting in haustra (pouches)

Question 15

What is diverticulosis?

Answer 15

haustra bulge outwards and become infected

Question 16

What is haustral shuttling?

Answer 16

Short distances in both directions
kneading of faecal mass - extracts as much water as possible

Question 17

What is segmental propulsion?

Answer 17

Peristalsis
both directions

Question 18

What is multihaustral propulsion?

Answer 18

Infrequent propulsions
Produced reflexively by gastrocolic reflex (fatty meals)
Moves faecal mass over large distances
Very regularly after meals

Question 19

What are the 5 triggers for mass movement in the colon?

Answer 19

Gastroileal reflex
Gastrocolic reflex
Irritation
Intense parasympathetic stimulation
Over-distension of a segment

Question 20

What are the 4 controls of colonic motility?

Answer 20

Basal electrical rhythm
Intrinsic nerves
extrinsic nerves
Endocrine/paracrine control

Question 21

What are ICCs increased by?

Answer 21

Stretcg
ACh
Histamine
Substance P
5-HT

Question 22

What are ICCS decreased by?

Answer 22

Noradrenaline
Adrenaline

Question 23

What is the intrinsic nerves for colon motility?

Answer 23

Myenteric plexus

Question 24

What is Hirschprung’s disease?

Answer 24

Congenital absence of ganglia
Tonic contraction of affected segment
Megacolon
Abdominal distension
Constipation

Question 25

What is Chaga's disease?

Answer 25

Infection with Trypanosoma cruzi damage to myenteric plexus Megacolon and megaoesophagus weight loss

Question 26

What is the effect of ACh?

Answer 26

Excitatory action on colonic smooth muscle

Question 27

What is the effect of adrenaline and noradrenaline?

Answer 27

Inhibitory action on colonic smooth muscle

Question 28

What is the role of the internal and smooth muscle sphincter?

Answer 28

Resting tone of anal canal Usually contracted (sympathetic) Relaxed by VIP/NO and presynaptic inhibition of sympathetic nerves Uncontrolled contraction

Question 29

What is the function of the external anal striated sphincter?

Answer 29

Squeeze pressure Motor drive from Onuf's nucleus of the pudendal nerve Increase in contraction from abdominal pressure rise Consciously choose to contract

Question 30

What is the function of the puborectalis?

Answer 30

Forms a sling around anal canal Changes the angle between rectum and anal canal

Question 31

What is defaecation?

Answer 31

Faeces enters and distends terminal segment after mass movement

Question 32

How is the rectum contracted?

Answer 32

By +ve feedback

Question 33

How is the internal anal sphincter relaxed?

Answer 33

Recto anal inhibitory reflex - role of NO

Question 34

What gives rise to sensation of urge?

Answer 34

Distension

Question 35

What is defaecation controlled by?

Answer 35

External anal sphincter and pelvic floor

Question 36

What causes faecal incontinence?

Answer 36

Obstetric injury Damage to pudendal nerve