Defaecation

Question 1

What are the 3 primordial embryonic layers? Which if these forms the GI tract?

Answer 1

Endoderm, Mesoderm and Ectoderm

Question 2

Which part of the GI tract is formed by each of the primordial embryonic layers

Answer 2

Endoderm- Gut tube formed by endoderm lining the yolk sac as the result of cranial and caudal folding

Mesoderm- Forms gut smooth muscle which lies around the endoderm layer

Ectoderm- Enteric nervous system

Question 3

What is the name of the intrinsic nervous system of the gut?

Answer 3

Enteric nervous system

Question 4

Name the 2 types of neural crest cells (NCC) which form the Enteric nervous stem

Answer 4

vagal, sacral and truncal NCC

Vagal and Sacral- parasympathetic innervation
Truncal- Sympathetic

Question 5

What is Hirschsprung disease?
What causes it?
What is the clinical symptom?
How is it treated?

Answer 5

• A birth defect of the intrinsic enteric nervous system.
• Causes absence of enteric nervous system (ENS) in the terminal part of the intestine
• Colon smooth muscle permanently contract becauses there is no Neuronal nitric oxide- (nNOS neurons) to relax the smooth muscle
• surgical removal of the aganglionic (does not have ganglia) part of the colon

Question 6

Name the 3 types of neural crest cells (NCC) which form the Extrinsic nervous stem and what type of innervation do they supply?

Answer 6

vagal, sacral and truncal NCC

Vagal and Sacral- parasympathetic innervation
Truncal- Sympathetic

Question 7

Name one function of extrinsic nervous system

Answer 7

Extrinsic nerves modulate the ENS function

Question 8

Urogenital opening and digestive opening are joined in the embryo, when are they separated?

Answer 8

By outgrowth and correct positioning of the urorectal septum.

Question 9

What is the cause of most anorectal malformations?

Answer 9

Failure of the urorectal septum to close the cloaca.

Question 10

What is defaecation? What is incontinence?

Answer 10

Dafaecation- begins with the urge to defaecate

Incontinence-
Dependent on an awareness of rectal filling
-he sensation of impending defaecation

Question 11

What can affected defaecation and incontinence? Name 2 associated conditions

Answer 11

Impaired sensory function

• rectal evacuatory dysfunction
• faecal incontinence

Question 12

List 4 factors which maintain faecal incontinence

Answer 12

• Normal rectal sensation
• Maintenance of angle
• Anal sphincters (IAS and EAS)
• Contraction of puborectalis muscle

Question 13

What is the flap valve?

How is it produced?

Answer 13

Flap valve- The mechanism where by anterior rectal wall is pushed downwards onto the anal canal when the intra-abdominal pressure rises

Via the puborectalis muscle

Question 14

What is the function of the flap valve?

Which actions activate the flap valve?

Answer 14

Stops the passage of faeces into the anal canal.

Straining/laughing/coughing

Question 15

What is the meaning of reservoir continence?

Answer 15

Ability of the rectum to retain stool

Question 16

Name 2 structures which prevent the progression of stool

Answer 16

1. Lateral angulations in the sigmoid colon

2. Transverse folds in the rectum

Question 17

What is another name for rectal transverse folds? How many are usually present and in which direction do the convex?

Answer 17

Valves of Houston
3
Upper and lowe convex to the right
Middle convexs to the left

Question 18

List the 4 stages of defaecation

Answer 18

1. Got to be full: filling
2. Have to know that it is full: sensation
3. Got to squeeze it: emptying
4. Got to take the lid off and put it back on: closure

Question 19

What is the main difference between continence and defaecation?

Answer 19

Continence- ability to keep it in

Defaecation- ability to let it out

Question 20

Describe the first stage of defaecaion and what it entails

Answer 20

Stage 1- Filling
-Stool is transported along the length of the colon by anterograde propulsion

• A series of mass movements usually persists for 10 to 30 min
• Then they cease but return perhaps a half day later

Question 21

Describe the features and function of the internal anal sphincters

Answer 21

-Internal Anal Sphincter
Continuously contracted
Essential for maintaining the closure of the resting pressure of the anal canal
Initiates the act of defecation by reflex dilation in response to rectal distension.

Question 22

Describe the features and function of the external anal sphincters

Answer 22

External Anal Sphincter
Contributes to the anal pressure when a bolus of stool in present in the anal canal
Known as the ‘squeeze pressure’.
Without this we would be unable to prevent leakage of mucus and gas.

Question 23

Describe the second stage of defaecaion how does it develop- infant to adult

Answer 23

Stage 2- sensation, conscious control of continence

neurocircuitry is present in infants- infants are not incontinent

Conscious control of defaecation is a learned response (toilet training)

Question 24

Where is the spinal defaecatory centre located? What happens when you cut the spinal cord above this level (paralysis) ?

Answer 24

S2-S4

leads to incontinence

Question 25

Describe the neurological component of the sensation stage in defaecation

Answer 25

Extrinsic afferent neurones mediate the conscious sensation of urgency Activated by mechanoreceptors

Question 26

What is rectal compliance? What is its function?

Answer 26

- The ability of the rectum to adapt to stretch | - Allows rectal contents to be accommodated for and for defaecation to be delayed.

Question 27

What is the Rectoanal inhibitory reflex? | At which stage of defaecation does it occure?

Answer 27

Extent of IAS relaxation depends on the degree of distension (how much it expands) - Larger volume, increased rectal distension so longer IAS relaxation - This allows some rectal contents to descend into the anal canal sensory mucosa  -Since the lower IAS exhibits higher resting pressures (contracts at rest) , incontinence does not occur. Thus, reflex relaxation of the IAS in response to rectal distension allows for ‘sampling’ of the rectal contents This helps distinguish flatus from faeces -Second stage of defaecation

Question 28

How is flatus distinguished from faeces?

Answer 28

The reflex relaxation of the IAS in response to rectal distension allows which for ‘sampling’ of the rectal contents. Assess what it is and how large it is

Question 29

Describe the defaecation stage of third stage of defecation

Answer 29

Stage 3- emptying and defaecation Defecation involves the relaxation of the EAS and puborectalis muscle This creates broader anorectal angle. Emptying-

Question 30

Describe the Emptying stage of third stage of defecation

Answer 30

- Rectal contents causes anal sphincters and puborectalis to relax - Then a Valsalva manoeuvre occurs (i.e. holding breath and forcibly trying to exhale a closed glottis, creating a pushing down effect). - Abdominal pressure ↑ and the muscles of the anterior abdominal wall tense up - Pressure reaches pelvis. - This pressure increase causes stool to enter lower rectum. Combined with recto-sigmoid contractions stool is pushed through the relaxed anal canal.

Question 31

Describe the fourth stage of defaecation

Answer 31

Fourth stage- Closure - Last bolus of stool is passed and then the ‘closing reflex’ of the EAS is stimulated by the releas of traction. - Upon voiding, inhibition IAS is removed causing it to contract - Voluntary contraction of EAS closes anus off. - Smooth muscles in sigmoid relax (enteric nervous system) re-establishing reservoir function.

Question 32

What is fecal incontinace?

Answer 32

-The inability to control bowel movements, causing stool to leak unexpectedly from the rectum.

Question 33

Name 4 causes of faecal incontinence

Answer 33

Diarrhoea Constipation, Muscle damage Nerve damage

Question 34

List 5 conditions associated with neuromuscular junction damage leading to incontinence

Answer 34

``` Pudendal nerve injury (childbirth) Hyper/hyposensitivity Impaired rectal sensorimotor function Sphincter dysfunction Slow-transit constipation ```

Question 35

List 2 Morphological abnormalities which can cause fecal incontinence

Answer 35

-Rectocoele (when rectum bulges into the posterior wall of the vagina) -Rectal prolapse/ intussusception (telescoping of the rectum into itself during straining), which cause an ‘obstruction’ on defaecation. Becomes detached, turns inside out, protrudes from anus. This causes obstruction during defaecation

Question 36

Describe the 4 types of rectal clinical investigations

Answer 36

1. Balloon expulsion 2. (High resolution) Manometry 3. Endoanal ultrasound 4. Proctogram (barium, MRI)

Question 37

What does the Balloon expulsion clinical test assess?

Answer 37

Rectal sensory function Hypersensitive associated with urge faecal incontinence Hyposenitive associated with evacuation difficulties

Question 38

What does the (High resolution) Manometry clinical test assess?

Answer 38

Neuromuscular assessment

Question 39

What does the Endoanal ultrasound clinical test assess?

Answer 39

``` structural damage (tears etc) Iatrogenic/obstetric ```

Question 40

What does the Proctogram (barium, MRI) clinical test assess?

Answer 40

Process of defaecation Structure/function relationships Rectocele/enterocele/Intussusception