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Metabolism 2 > Defecation > Flashcards

Defecation Flashcards

1
Q

what are the three embryological layers that the gut tube is made out of

A
  • ectoderm
  • mesoderm
  • endoderm
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2
Q

describe what the three embryological layers of the gut tube are made out of

A
  • Ectoderm - skin of epidermis, nerves exoskeleton)
  • Mesoderm - muscle (cardiac, skeletal, smooth), tube cells of the kidney, red blood cells (organs)
  • Endoderm - lung cell, thyroid cells, digestive cells of the pancreas (inner lining of organs)
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3
Q

what is the gut tube fromed from

A
  • Gut tube is formed from endoderm lining the yolk sac as the result of cranial and caudal folding.
  • The gut smooth muscle is formed from mesoderm around the primitive gut endoderm
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4
Q

what 3 things is the primitive gut tube made out of

A

Foregut
Midgut
Hindgut

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5
Q

when does the primitive gut tube develop and how

A

weeks 3-4

- incorporates the yolk sac during the craniocaudal and lateral folding of the embryo

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6
Q

What does the foregut give rise to

A

esophagus, stomach, liver, gallbladder, bile ducts, pancreas and proximal duodenum.

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7
Q

what does the midgut give rise to

A

distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal 2/3 of transverse colon

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8
Q

what does the hindgut develop into

A

The hindgut becomes distal 1/3 of the transverse colon, descending colon, sigmoid colon and the upper anal canal.

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9
Q

what is the supply of the

  • foregut
  • midgut
  • hindgut
A
  • foregut - celiac artery
  • midgut - superior mesenteric artery
  • hindgut - inferior mesenteric artery
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10
Q

what dives the foregut into the oesophagus and trachea

A

The tracheoesophageal septum divides foregut into the oesophagus and trachea

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11
Q

if the tracheoesophageal septum does not develop what happens

A

Failure of the Tracheoesophageal septum to fully develop results in Tracheoesophageal fistula (TEF) and or esophageal atresia.

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12
Q

name some foregut clinical problems

A

Oesophageal atresia

Tracheo-oesophageal fistula (TEF)

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13
Q

name some midgut clinical problems

A
  • duodenal atresia
  • meckel’s diverticulum
  • malrotation
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14
Q

describe some midgut clinical problems

A

Duodenal atresia is due to failed canalization.

Meckel’s diverticulum occurs when a remnant of the yolk sac (Vitelline duct) persists.

Malrotation occurs if the midgut does not complete the rotation prior to returning to the abdomen.

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15
Q

Where does the Distal 1/3 of the transverse colon, descending colon and sigmoid colon develop from

A

Distal 1/3 of the transverse colon, descending colon and sigmoid colon develop from the cranial end of the hindgut.

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16
Q

where does the upper anal canal in the hindgut develop from

A

Upper anal canal develops from the terminal end of the hindgut with the urorectal septum dividing the upper anal canal and the urogenital sinus during 6th week.

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17
Q

What is the pectinate line

A

The pectinate line is the junction of proctodeum ectoderm and hindgut endoderm.

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18
Q

what gives rise to the anal membrane and the urogential membrane

A

7th week, the urorectal septum fuses with the cloacal membrane, giving rise to the anal membrane and the urogenital membrane

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19
Q

describe how the anal canals develop

A

The anal membrane ruptures during the 8th week allowing communication between the anal canal and the amniotic fluid.

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20
Q

what are most anorectal malformations due to

A

Most anorectal malformations are linked to failure of the urorectal septum to close the cloaca.

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21
Q

what is an imperforate anus

A
  • this is caused by failure of rupture of the anal membrane
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22
Q

What is a rectoanal atresia

A

failure of recanalisation or defective blood supply of the developing part.

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23
Q

What is a persistent clacoa

A
  • complete failure of development of the urorectal septum.
  • F>M
  • where the urinary bladder, vagina and rectum open in one cavity.
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24
Q

what is the intrinsic nervous supply of the gut

A

ENS - dervied from the vagal and sacral neural crest cells

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25
Q

what is the extrinsic nervous supply of the gut

A

vagal and sacral NCC forming the parasympathetic innervation and truncal NCC forming the sympathetic innervation.

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26
Q

what are the two nervous supply of the gut

A

intrinsic

extrinsic

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27
Q

Extrinsic nerve…

A

modulates the ENS (intrsinic nervous system of the gut0

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28
Q

What is hirschsprungs disease

A
  • briht defect charactersied by the absence of the enteric nervous system in the terminal part of the intestine
  • this causes the colon smooth msucle to permanelty be contracted
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29
Q

what are the symptoms of Hirschsprungs disease

A
  • failing to pass
  • meconiumwithin 48 hours
    a swollen belly
  • vomiting green fluid (bile)
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30
Q

How is Hirschprungs disease treated

A
  • surgical resection of the aganglionic part of the colon ( part of the colon with no ENS)
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31
Q

what is continence usually maintained by

A

anal canal

pelvic floor musculature

rectum

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32
Q

what is the role of the rectum

A
  • store or expel stool
  • these both require cortical sensory awareness acting in conjunction with intramural and spinal reflexes that ensure defection
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33
Q

what is the role of the anal canal

A

Anal canal helps to maintain faecal continence and control defecation

34
Q

what do the pelvic muscles do

A
  • divides abdominal cavity from perineum
35
Q

what are the three muscles that make up the levator ani

A
  • puborectalis
  • puboccocygenous
  • illiococygenous
36
Q

what are the muscles that make up the pelvic wall

A

Levator Ani

  • puborectalis
  • puboccocygenous
  • illiococygenous

Coccygeous

37
Q

where does puborectalis attach from

A

Passes directly backward from the back of the pubic symphysis to form a ‘U-shaped loop’ that slings the rectum to the pubis.

38
Q

what type of muscle is the puborectalis

A

striated muscle

39
Q

what does the puborectalis surround

A
  • rectum
  • vagina
  • urethra
40
Q

what sphincter does puborectailis support

A
  • it supports the EAS

- assists in creating the anorectal angle

41
Q

what is the role of puborectalis

A

maintains the angle between the anal canal and rectum

42
Q

what makes up most of the pelvic floor

A

levator ani muscle

43
Q

What does continence mean

A
  • this refers to self control it is the ability to hold it in
44
Q

What is faecal continence maintained by

A

Anal sphincters

  • Internal anal sphincter (IAS)
  • External anal sphincter (EAS)

Pelvic floor muscles
- Puborectalis muscle

45
Q

what is the difference between the external anal sphincter and internal anal sphincter

A

External anal sphincter
- voluntary muscle which encircles the internal anal sphincter

internal anal sphincter

  • involuntary
  • thickened muscle
  • downward continuation of the inner circular muscle coat of the rectum surrounding the entire anal canal
46
Q

why is voluntary control of the external anal sphincter important

A

Voluntary control of the EAS is key in the voluntary deferring of evacuation until a socially opportune moment

47
Q

what is the nerve supply of the rectum, anus, bladder and urethra

A

S2-S4 parasympathetic supply = pudendal nerve

48
Q

S2, S3, S4 keeps…

A

S2,3,4 keeps the 3 P‘s off the floor (Penis, Poo, and Pee)

49
Q

what are the nerves responsible for continence

A

S2-S4 parasympathetic supply = pudendal nerve

50
Q

describe the nerve supply of the External anal sphincter

A
  • supplied by the inferior rectal branch of the pudendal nerve
  • which gives of the inferior rectal nerves

inferior rectal nerves divided into

  • perineal nerve and the dorsal nerve of the penis in males
  • dorsal nerve of the clitoris in females
51
Q

describe the nerve supply of the internal anal sphincter

A
  • enteric nervous system (autonomic nervous system)
  • sympathetic - L1-L2 via hypogastric nerves which are excitatory
  • parasympathetic - S2-S4 pelvic nerves are inhibitory
52
Q

what are the three reflexes that make up defaecation

A
  • initiation reflex - urge to go
  • defecation reflex - voiding reflex - opening of the anus
  • closure reflex - closing of the anus
53
Q

what has to relax in defecation

A

Defecation involves the relaxation of the EAS and puborectalis muscle, to create a broader anorectal angle.

54
Q

describe how filling happens in the anus

A
  • internal anal sphincter is in a continuously tonic state and is essential for maintaining the closure of the resting pressure of the anal canal
  • it initiates the act of defecation by reflex dilation in response to rectal distension
  • when a bolus of stool is in the anal canal the EAS contributes to the anal pressure which is know as the squeeze pressure
  • without this resting pressure we would be unable to prevent leakage of mucus and gas
55
Q

what is the rectoanal inhibitory reflex

A

this is when the anal canal distends and results in internal anal sphincter relaxation allowing slight distension
- this allows for sampling of the rectal contents and helps distinguish flatus from faeces

56
Q

what is sphincter function

A

Resting pressure,
Squeeze pressure,
Endurance Squeeze,
Rectoanal inhibitory reflex (RAIR)

57
Q

what is rectal sensation

A

hypersensitivity (associated with faecal incontinence)

hyposensitivity (associated with constipation

58
Q

more than 80% of children with constipation are…

A

faecal incontinence

59
Q

What is constipation

A
  • purely symptomatic - not a diagnosis

- can mean different things so important to ask the patient what they think it is

60
Q

who does constipation effect

A

more females than males

elderly

61
Q

what is the difference between defecation and continence

A

DEFAECATION
- begins with the urge to defaecate

CONTINENCE

  • dependent on an awareness of rectal filling
  • the sensation of impending defaecation
62
Q

what happens if continence is impaired

A
  • rectal evacuatory dysfunction
  • faecal incontinence
  • both
63
Q

how is continence felt

A
  • extrinsic afferent neurones mediate conscious sesation of urgency which is activated by mechanoreceptors
64
Q

what is the ability of the rectum to adapt to the imposed stretch called

A

rectal compliance

65
Q

What is hypersenstivity

A
  • reduced sensory threshold to volumetric rectal distension
  • associated with urge FI
  • bowel disorder, IBS, intussusception
66
Q

What is hyposensitive

A
  • increased sensory threshold to volumetric rectal distension
  • associated with evacuation difficulites, functional disorders, constipation
67
Q

what is normal transit constipation

A
  • this is normal transit yet the patient feels constipated

- usually overlaps with OBS since pain are bloating are common

68
Q

what is slow transit constipation

A
  • more common in young women and children
  • infrequency and slow movement of stool
  • bloating, abdominal pain and infrequent urge to defecate
69
Q

what is rectal evacuatory disorder

A
  • constipation common in children
  • associated with hard/painful stools
  • bloating, abdominal pain and infrequent urge to defecate
70
Q

what is disordered defecation

A

usually due to dysfunction of pelvic floor and anal sphincters.

71
Q

What pelvic wall abnormalities can occur

A

renal prolapse - when the rectal walls slide through the anus - tissues holding the rectum have weakend so it is no longer supported and pressure in the abdomen increases

rectal intussusception - this is a telescoping of the rectum into itself during straining which causes an obstruction on defecation

72
Q

What is daefection dyssynergia

A

is common in women and children and affects up to one half of patients with chronic constipation.
- due to the inability to coordinate the abdominal and pelvic floor muscles to evacuate stools

73
Q

what are the secondary things that can cause constipation

A

Endocrine: Diabetes; Hypothyroidism; Hyperparathyroidism; glucagonoma

Neurological: spinal injury; Parkinson’s disease; MS, autonomic neuropathy;

Psychogenic: affective disorders; eating disorders; dementia or learning difficulty

Metabolic: Hypercalcaemia; uraemia; hypokalaemia; amyloidosis; lead poisoning.

Colonic: tumour; diverticular disease stricture; ischaemia

Anal: Fissure; polyp; tumour

Physiological: pregnancy; old age

74
Q

what is faecal incontinence

A

Involuntary passage of rectal content (gas or stool) and it is a source of major embarrassment to the sufferer.
- more common with increasing age

75
Q

what clinical things do you look for in faecal incontience

A

External: visible soiling; excoriation (scars/defects)

Internal: organic disease (piles, fissures, fistula, tumour); defects; tone; squeeze; pelvic floor dysnergia; rectocele/intussusception (internal prolapse)

76
Q

what are the two types of faecal incontinence

A

passive incontinence

urge incontinence

77
Q

what is the difference between passive and urge incontinence

A

Passive
- structural and function lesion on the intenral sphincter

urge
- structural and function lesion on the external sphincter

78
Q

what can go wrong with the anus

A

Structure problems

  • obstetric sphincter tear
  • iatrogenic sphincter tear
  • radiation damage
  • congenital malformations

Function problems
- pudendal neuropathy

79
Q

How do you manage constiption

A

Diet:
Normal transit – augment dietary fibre and liquid intake and fibre supplements to those who can’t manage this.

Slow transit – less fibre as they tend to exacerbate bloating and does not help accelerate transit.

Laxatives:
Stimulant (Senna, bisacodyl) - better as required than regular to avoid laxative dependence;

Stool softeners (docusate) used as adjuvant agents; osmotic agents (mg salts, Lactulose) effective in slow transit and allow dose adjustment according to response.

80
Q

what drugs are used to manage consitpation

A

laxatives

81
Q

what is non conservative management for constipation

A
  • behavioural therapy
  • transanal irrigation - water pump systme
  • surgery
  • psychological therapy
  • neuromodulation - posterior tibial nerve stimulation and sacral nerve stimulation

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