Defecation Flashcards
what are the three embryological layers that the gut tube is made out of
- ectoderm
- mesoderm
- endoderm
describe what the three embryological layers of the gut tube are made out of
- 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)
what is the gut tube fromed from
- 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
what 3 things is the primitive gut tube made out of
Foregut
Midgut
Hindgut
when does the primitive gut tube develop and how
weeks 3-4
- incorporates the yolk sac during the craniocaudal and lateral folding of the embryo
What does the foregut give rise to
esophagus, stomach, liver, gallbladder, bile ducts, pancreas and proximal duodenum.
what does the midgut give rise to
distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, and proximal 2/3 of transverse colon
what does the hindgut develop into
The hindgut becomes distal 1/3 of the transverse colon, descending colon, sigmoid colon and the upper anal canal.
what is the supply of the
- foregut
- midgut
- hindgut
- foregut - celiac artery
- midgut - superior mesenteric artery
- hindgut - inferior mesenteric artery
what dives the foregut into the oesophagus and trachea
The tracheoesophageal septum divides foregut into the oesophagus and trachea
if the tracheoesophageal septum does not develop what happens
Failure of the Tracheoesophageal septum to fully develop results in Tracheoesophageal fistula (TEF) and or esophageal atresia.
name some foregut clinical problems
Oesophageal atresia
Tracheo-oesophageal fistula (TEF)
name some midgut clinical problems
- duodenal atresia
- meckel’s diverticulum
- malrotation
describe some midgut clinical problems
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.
Where does the Distal 1/3 of the transverse colon, descending colon and sigmoid colon develop from
Distal 1/3 of the transverse colon, descending colon and sigmoid colon develop from the cranial end of the hindgut.
where does the upper anal canal in the hindgut develop from
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.
What is the pectinate line
The pectinate line is the junction of proctodeum ectoderm and hindgut endoderm.
what gives rise to the anal membrane and the urogential membrane
7th week, the urorectal septum fuses with the cloacal membrane, giving rise to the anal membrane and the urogenital membrane
describe how the anal canals develop
The anal membrane ruptures during the 8th week allowing communication between the anal canal and the amniotic fluid.
what are most anorectal malformations due to
Most anorectal malformations are linked to failure of the urorectal septum to close the cloaca.
what is an imperforate anus
- this is caused by failure of rupture of the anal membrane
What is a rectoanal atresia
failure of recanalisation or defective blood supply of the developing part.
What is a persistent clacoa
- complete failure of development of the urorectal septum.
- F>M
- where the urinary bladder, vagina and rectum open in one cavity.
what is the intrinsic nervous supply of the gut
ENS - dervied from the vagal and sacral neural crest cells
what is the extrinsic nervous supply of the gut
vagal and sacral NCC forming the parasympathetic innervation and truncal NCC forming the sympathetic innervation.
what are the two nervous supply of the gut
intrinsic
extrinsic
Extrinsic nerve…
modulates the ENS (intrsinic nervous system of the gut0
What is hirschsprungs disease
- 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
what are the symptoms of Hirschsprungs disease
- failing to pass
- meconiumwithin 48 hours
a swollen belly - vomiting green fluid (bile)
How is Hirschprungs disease treated
- surgical resection of the aganglionic part of the colon ( part of the colon with no ENS)
what is continence usually maintained by
anal canal
pelvic floor musculature
rectum
what is the role of the rectum
- store or expel stool
- these both require cortical sensory awareness acting in conjunction with intramural and spinal reflexes that ensure defection
what is the role of the anal canal
Anal canal helps to maintain faecal continence and control defecation
what do the pelvic muscles do
- divides abdominal cavity from perineum
what are the three muscles that make up the levator ani
- puborectalis
- puboccocygenous
- illiococygenous
what are the muscles that make up the pelvic wall
Levator Ani
- puborectalis
- puboccocygenous
- illiococygenous
Coccygeous
where does puborectalis attach from
Passes directly backward from the back of the pubic symphysis to form a ‘U-shaped loop’ that slings the rectum to the pubis.
what type of muscle is the puborectalis
striated muscle
what does the puborectalis surround
- rectum
- vagina
- urethra
what sphincter does puborectailis support
- it supports the EAS
- assists in creating the anorectal angle
what is the role of puborectalis
maintains the angle between the anal canal and rectum
what makes up most of the pelvic floor
levator ani muscle
What does continence mean
- this refers to self control it is the ability to hold it in
What is faecal continence maintained by
Anal sphincters
- Internal anal sphincter (IAS)
- External anal sphincter (EAS)
Pelvic floor muscles
- Puborectalis muscle
what is the difference between the external anal sphincter and internal anal sphincter
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
why is voluntary control of the external anal sphincter important
Voluntary control of the EAS is key in the voluntary deferring of evacuation until a socially opportune moment
what is the nerve supply of the rectum, anus, bladder and urethra
S2-S4 parasympathetic supply = pudendal nerve
S2, S3, S4 keeps…
S2,3,4 keeps the 3 P‘s off the floor (Penis, Poo, and Pee)
what are the nerves responsible for continence
S2-S4 parasympathetic supply = pudendal nerve
describe the nerve supply of the External anal sphincter
- 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
describe the nerve supply of the internal anal sphincter
- enteric nervous system (autonomic nervous system)
- sympathetic - L1-L2 via hypogastric nerves which are excitatory
- parasympathetic - S2-S4 pelvic nerves are inhibitory
what are the three reflexes that make up defaecation
- initiation reflex - urge to go
- defecation reflex - voiding reflex - opening of the anus
- closure reflex - closing of the anus
what has to relax in defecation
Defecation involves the relaxation of the EAS and puborectalis muscle, to create a broader anorectal angle.
describe how filling happens in the anus
- 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
what is the rectoanal inhibitory reflex
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
what is sphincter function
Resting pressure,
Squeeze pressure,
Endurance Squeeze,
Rectoanal inhibitory reflex (RAIR)
what is rectal sensation
hypersensitivity (associated with faecal incontinence)
hyposensitivity (associated with constipation
more than 80% of children with constipation are…
faecal incontinence
What is constipation
- purely symptomatic - not a diagnosis
- can mean different things so important to ask the patient what they think it is
who does constipation effect
more females than males
elderly
what is the difference between defecation and continence
DEFAECATION
- begins with the urge to defaecate
CONTINENCE
- dependent on an awareness of rectal filling
- the sensation of impending defaecation
what happens if continence is impaired
- rectal evacuatory dysfunction
- faecal incontinence
- both
how is continence felt
- extrinsic afferent neurones mediate conscious sesation of urgency which is activated by mechanoreceptors
what is the ability of the rectum to adapt to the imposed stretch called
rectal compliance
What is hypersenstivity
- reduced sensory threshold to volumetric rectal distension
- associated with urge FI
- bowel disorder, IBS, intussusception
What is hyposensitive
- increased sensory threshold to volumetric rectal distension
- associated with evacuation difficulites, functional disorders, constipation
what is normal transit constipation
- this is normal transit yet the patient feels constipated
- usually overlaps with OBS since pain are bloating are common
what is slow transit constipation
- more common in young women and children
- infrequency and slow movement of stool
- bloating, abdominal pain and infrequent urge to defecate
what is rectal evacuatory disorder
- constipation common in children
- associated with hard/painful stools
- bloating, abdominal pain and infrequent urge to defecate
what is disordered defecation
usually due to dysfunction of pelvic floor and anal sphincters.
What pelvic wall abnormalities can occur
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
What is daefection dyssynergia
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
what are the secondary things that can cause constipation
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
what is faecal incontinence
Involuntary passage of rectal content (gas or stool) and it is a source of major embarrassment to the sufferer.
- more common with increasing age
what clinical things do you look for in faecal incontience
External: visible soiling; excoriation (scars/defects)
Internal: organic disease (piles, fissures, fistula, tumour); defects; tone; squeeze; pelvic floor dysnergia; rectocele/intussusception (internal prolapse)
what are the two types of faecal incontinence
passive incontinence
urge incontinence
what is the difference between passive and urge incontinence
Passive
- structural and function lesion on the intenral sphincter
urge
- structural and function lesion on the external sphincter
what can go wrong with the anus
Structure problems
- obstetric sphincter tear
- iatrogenic sphincter tear
- radiation damage
- congenital malformations
Function problems
- pudendal neuropathy
How do you manage constiption
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.
what drugs are used to manage consitpation
laxatives
what is non conservative management for constipation
- behavioural therapy
- transanal irrigation - water pump systme
- surgery
- psychological therapy
- neuromodulation - posterior tibial nerve stimulation and sacral nerve stimulation
