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Metabolism Y2 > Defaecation > Flashcards

Defaecation Flashcards

1
Q

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

A

Endoderm, Mesoderm and Ectoderm

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2
Q

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

A

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

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3
Q

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

A

Enteric nervous system

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4
Q

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

A

vagal, sacral and truncal NCC

Vagal and Sacral- parasympathetic innervation
Truncal- Sympathetic

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5
Q

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

A
  • 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
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6
Q

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

A

vagal, sacral and truncal NCC

Vagal and Sacral- parasympathetic innervation
Truncal- Sympathetic

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7
Q

Name one function of extrinsic nervous system

A

Extrinsic nerves modulate the ENS function

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8
Q

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

A

By outgrowth and correct positioning of the urorectal septum.

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9
Q

What is the cause of most anorectal malformations?

A

Failure of the urorectal septum to close the cloaca.

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10
Q

What is defaecation? What is incontinence?

A

Dafaecation- begins with the urge to defaecate

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

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11
Q

What can affected defaecation and incontinence? Name 2 associated conditions

A

Impaired sensory function

  • rectal evacuatory dysfunction
  • faecal incontinence
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12
Q

List 4 factors which maintain faecal incontinence

A
  • Normal rectal sensation
  • Maintenance of angle
  • Anal sphincters (IAS and EAS)
  • Contraction of puborectalis muscle
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13
Q

What is the flap valve?

How is it produced?

A

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

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14
Q

What is the function of the flap valve?

Which actions activate the flap valve?

A

Stops the passage of faeces into the anal canal.

Straining/laughing/coughing

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15
Q

What is the meaning of reservoir continence?

A

Ability of the rectum to retain stool

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16
Q

Name 2 structures which prevent the progression of stool

A
  1. Lateral angulations in the sigmoid colon

2. Transverse folds in the rectum

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17
Q

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

A

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

18
Q

List the 4 stages of defaecation

A
  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
19
Q

What is the main difference between continence and defaecation?

A

Continence- ability to keep it in

Defaecation- ability to let it out

20
Q

Describe the first stage of defaecaion and what it entails

A

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
21
Q

Describe the features and function of the internal anal sphincters

A

-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.

22
Q

Describe the features and function of the external anal sphincters

A

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.

23
Q

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

A

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)

24
Q

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

A

S2-S4

leads to incontinence

25
Q

Describe the neurological component of the sensation stage in defaecation

A

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

26
Q

What is rectal compliance? What is its function?

A
  • The ability of the rectum to adapt to stretch

- Allows rectal contents to be accommodated for and for defaecation to be delayed.

27
Q

What is the Rectoanal inhibitory reflex?

At which stage of defaecation does it occure?

A

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

28
Q

How is flatus distinguished from faeces?

A

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

29
Q

Describe the defaecation stage of third stage of defecation

A

Stage 3- emptying and defaecation

Defecation involves the relaxation of the EAS and puborectalis muscle
This creates broader anorectal angle.

Emptying-

30
Q

Describe the Emptying stage of third stage of defecation

A
  • 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.
31
Q

Describe the fourth stage of defaecation

A

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.
32
Q

What is fecal incontinace?

A

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

33
Q

Name 4 causes of faecal incontinence

A

Diarrhoea
Constipation,
Muscle damage
Nerve damage

34
Q

List 5 conditions associated with neuromuscular junction damage leading to incontinence

A 
Pudendal nerve injury (childbirth)
Hyper/hyposensitivity
Impaired rectal sensorimotor function
Sphincter dysfunction
Slow-transit constipation
35
Q

List 2 Morphological abnormalities which can cause fecal incontinence

A

-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

36
Q

Describe the 4 types of rectal clinical investigations

A
  1. Balloon expulsion
  2. (High resolution) Manometry
  3. Endoanal ultrasound
  4. Proctogram (barium, MRI)
37
Q

What does the Balloon expulsion clinical test assess?

A

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

38
Q

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

A

Neuromuscular assessment

39
Q

What does the Endoanal ultrasound clinical test assess?

A 
structural damage (tears etc)
Iatrogenic/obstetric
40
Q

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

A

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

Metabolism Y2 (14 decks)

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