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MET 2 > Defecation > Flashcards

Defecation Flashcards

1
Q

Where is the primitive gut tube derived from

A

Dorsal part of the yolk sac

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2
Q

What ‘derm’ is the gut tube derived from

A

Endoderm

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3
Q

Describe how the folding occurs to form the gut

A
  • Somatic mesoderm applied to body wall to give rise to parietal peritoneum
  • Visceral mesoderm wraps around gut tube to form mesenteries that suspend gut tube within cavity
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4
Q

In which 2 directions does embryological folding occur to make the gut tube

A

Cranio-caudal

Lateral

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5
Q

What pockets are formed from the folding of the gut tube

A

Anterior intestinal portal

Posterior intestinal portal

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6
Q

Name the 3 sections of the primitive gut and their blood supply

A 
Foregut= coeliac artery
Midgut= superior mesenteric artery
Hindgut= inferior mesenteric artery
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7
Q

What is an imperforate anus

A

Caused by failure of rupture of anal membrane- inperfect development

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8
Q

What is rectoanal atresia

A

Failure of recanalisation or defective blood supply to developing part

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9
Q

What is persistent cloaca

A

Complete failure of development of urorectal septum

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10
Q

What are the symptoms of Hirschsprungs disease

A 
Failing to pass meconium withiin 48 hours
Swollen belly
Vomiting bile (green)
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11
Q

What is Hirschsprungs disease

A

Congenital megacolon due to a lack of enteric neurons in the distal portion of the gut. Ganglia derived from neural crest that migrate from the neural folds to the wall of bowel

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12
Q

Name 2 things that can cause water absorption in the small intestine

A

Passively due to result of osmotic gradient produced by active transport
Aldosterone

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13
Q

What % of the remaining volume of water is absorbed by the large intestine

A

90

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14
Q

Define diarrhoea and constipation

A

Diarrhoea–> excessive water secretion in the faeces

Constipation–> decreased water secretion in the faeces

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15
Q

What maintains normal faecal continence (3)

A
  • Anal canal
  • Pelvic floor musculature
  • Rectum
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16
Q

What is the role of the rectum

A

Stores or expels stool

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17
Q

What is required by the rectum to either store or expel a stool

A

Cortical sensory awareness in conjunction with intramural and spinal reflexes

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18
Q

What is the role of anal canal

A

Maintains faecal continence and controls defecation

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19
Q

Describe the muscle found in the internal anal sphincter

A

Thickened muscle which is a downward continuation of inner circular muscle coat of rectum

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20
Q

What does the internal anal sphincter surround

A

The entire anal canal

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21
Q

Is the external or internal anal sphincter voluntary

A

External

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22
Q

Name the pelvic floor musclesw

A

Pubococcygeus
Puborectalis
Iliococcygeus
Ishiococcygeus

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23
Q

Describe the structure of the puborectalis

A
  • Passes behind the back of pubic symphysis to form a U shaped loop
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24
Q

What is the function of the puborectalis

A

Supports EAS assists in creating anorectal angle

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25
Q

Which muscle is the largest of the pelvic floor

A

Levator ani

26
Q

What do nerves S2, 3 and 4 effect

A

Rectum, anus, bladder and urethra

27
Q

What is the parasympathetic supply that aids continence

A

S2-S4 (pudendal nerve)

28
Q

Which branch of the pudendal nerve suplies the external anal sphincter

A

Inferior rectal branch

29
Q

What terminal branches does inferior rectal branch into? What do these supply

A

Perineal nerve
Dorsal nerve of the penis
Dorsal nerve of clitoris

30
Q

What innervates the internal anal sphincter

A

Enteric nervous system

31
Q

What is the sympathetic and parasympathetic innervation of internal anal sphincter? What is the effect

A
  • Symp= L1 and L2 via hypogastric nerve. Excitatory

- Para= S2-S4. Pelvic nerve. Inhibitory

32
Q

What does continence depend upon

A
  • Awareness of rectal filling

- Sensation of impending defecation

33
Q

What does continence require

A
  • Contraction of puborectalis
  • Maintenance of ano-rectal angle
  • Normal rectal sensation
  • Sphincter contraction
34
Q

What does the tonic

contraction of the puborectalis muscle create?

A

Flap valve

35
Q

What is the role of the flap valve

A

Maintains the angle so the rectal wall is pushed downwards when intra-abdominal pressure is increased

36
Q

Define reservoir continence

A

Ability of rectum to retain stool

37
Q

What anatomical adaptations provide a mechanical barrier

A

Lateral angulations in sigmoid colon

Valves of Houston

38
Q

Define rectal compliance

A

Ability of rectum to adapt to imposed stretch

39
Q

What is the advantage of rectal compliance

A

Allows rectal contents to be accomodated for and for defecation to be delayed

40
Q

Describe what is meant by the rectoanal inhibitory reflex

A
  • Extent of relaxation depends on degree of distention
  • Large volume rectal distension the IAS relaxation can be prolonged
  • Slight distention only particular relaxation occur
41
Q

What makes defecation possible

A
  • Initiation of reflex
  • Defecation reflex (opening of the anus)
  • Closure reflex (closure of anus)
42
Q

What muscles relax during defecation

A

EAS and puborectalis

43
Q

How does anorectal angle change during defecation

A

Becomes broader

44
Q

What is meant by Valsalva manoeuvre

A

Holding breath, forcibly, closed glottis

45
Q

What steps occur in the closure reflex

A
  • Closing reflex of EAS stimulation by traction releases
  • Receptor adaptation in the ampulla recti removes inhibitory drive to IAS
  • Voluntary contraction of EAS closes anus off
46
Q

How does IAS behave during defecation

A

Reflex relaxation in response to rectal distention

47
Q

How does reflex relaxation of the IAS help distinguish flatus from faeces

A

The relaxation in response to rectal distention allows for sampling of rectal contents

48
Q

What are the definitions/ criteria for constipation

A
  • Infrequent stool (<3 a week) or
  • Passage of hard stools >25% of the time or
  • Sensation of incomplete evacuation >25% of the time
49
Q

What is meant by neural transit constipation

A
  • Normal transit but patient feels constipated
50
Q

What is meant by slow transit constipation

A

Infrequency and slow movement of stool

Bloating, abdominal pain and infrequent urge to defecate

51
Q

What usually causes disordered defecation

A

Dysfunction of pelvic floor/ anal sphincters

Structural abnormalities such as rectocoele (bulging of rectum to posterior wall of vagina)

52
Q

What is passive incontience usually caused to

A

Structural/ functional lesion of the internal anal sphincter

53
Q

What is urge incontinence usually caused by

A

Structural/ functional lesion of external anal sphincter

54
Q

What can be structurally wrong with the anus

A

Obstetric sphincter tear
Latrogenic sphincter tear
Radiation damage
Congenital malformations

55
Q

What can be functionally wrong with the anus

A

Pudendal neuropathy

56
Q

What are hypersensitivity of rectal sensation and hyposensitivity of rectal sensation related to

A 
Hyper= faecal incontinence
Hypo= constipation
57
Q

Define hypersensitive rectal sensation

A

Reduced sensory threshold to volumetric rectal distension

58
Q

What can cause hypersensitive rectal sensation

A

Proctitis, long term consequences of pelvic radiotherapy, bowel disorder, IBS

59
Q

Define hyposensitive rectal sensation

A

Increased sensory threshold to volumetric rectal distention

60
Q

Summarise the process of normal defecation

A
  • Sensory perception of stool
  • Rectal distension
  • Contract diaphragm, abdomen and rectal muscles
  • Relax EAS
  • Relax puborectalis
61
Q

Summarise the process of incontinence

A
  • Low resting/ low squeeze sphincter processes
  • Weakness of puborectalis
  • Neuropathy
  • Altered rectal or anal sensation
  • Diarrheal conditions
  • Diminished rectal capacity

MET 2 (32 decks)

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