Defecation and anal anatomy Flashcards
What is the cause of an imperforate anus/anorectal malformation
- failure of rupture of the anal membrane
- -> failure of communication of the endodermal and ectodermal portions of the anal canal
What is persistent cloaca?
- complete failure of development of the urorectal septum
- occurs more in females than males –> where the urinary urinary bladder, vagina and rectum open in one cavity
What is Hirschsprung’s disease?
- birth defect (~1 in 5,000 newborns)
- characterised by the absence of enteric nervous system in the terminal part of the intestine
- causes colon smooth muscle to be permanently contracted (no nNOS neurones to relax)
What are the symptoms of Hirschsprung’s disease?
- failing to pass meconium within 48 hours
- swollen belly
- vomiting bile (will appear green)
How is Hirschsprung’s disease treated?
surgical resection fo the aganglionic part of the colon
Compare the external and internal anal sphincter.
IAS:
- involuntary and thickened muscles
- downward continuation of the inner circular muscle coat of the rectum
- surrounds the entire anal canal
innervated by the ENS (myenteric plexus) - innervated by autonomic nervous system
EAS:
- voluntary muscle which encircles the IAS
- supplies by the inferior rectal branch of the pudendal nerve - gives off inferior rectal nerves
- -> divides into perineal and dorsal nerves in males and just the dorsal nerve in females
What nerves are responsible for continence?
Pudendal nerve (S2-S4 parasympathetic supply)
What are the S+S of constipation?
- infrequent stools (<3 per week)
- passage of hard stools (>25% of the time)
- sensation of incomplete evacuation (>25% of the time)
Explain continence in terms of defecation?
Defecation = beings with the urge to defecate
Continence:
- dependence on awareness of rectal filling
- sensation of impending defection
- extrinsic afferent neurones mediate conscious sensation of urgency which is activated by mechanoreceptors
*ability o the rectum to adapt to the imposed stretch = rectal compliance
What tests can be done to check colonic transit?
- radio-opaque/transit xray
- colonic scintigraphy
What tests can be done to check evacuation?
- MRI proctogram
- barium proctogram
- balloon expulsion test
What tests can be done to evaluate the sphincter?
- endoanal ultrasound
- endoanal MRI
- anorectal manometry
Compare hypersensitive and hyposensitive rectal sensation.
Hypersensitive:
- reduced sensory threshold to volumetric rectal distension
- bowel disorder, IDK, intussusception
Hyposensitive:
- increased sensory threshold to volumetric recta distension
What is normal transit constipation?
- normal transit yet patient feel constipated
- usually secondary to perceived difficulty with defecation and hard stools
- overlap with IBS since pain and bloating are common
What is slow transit constipation?
- common in young women and children
- infrequency and slow movement of stool
- bloating, abdominal pain and infrequent urger to defecate
What is rectal evacuatory disorder?
- common in children
- associated with hard/painful stools, per rectal bleeding
- bloating, abdominal pain and infrequent urge to defecate
Why does rectal prolapse usually occur?
- rectal wall slides out through the anus as a result of weakness in the muscles and ligaments holding it in place
- no longer supported and when the pressure increases in the abdomen the muscles of the rectum aren’t strong enough to hold it in
What is rectal intussusception?
- telescoping of the rectum into itself during training
- cna cause an obstruction on defecation
What is defecation dysnergia?
- dysfunction of the pelvis floor and anal sphincters
- inability to coordinate the abdominal and pelvic floor muscles to evacuate stools
What are the secondary causes of constipation?
- endocrine: diabetes, hypothyroidism
- neurological: spinal injury, Parkinson’s disease
- psychogenic: affective disorders, eating disorders
- metabolic
- colonic: tumour, diverticular disease
- anal: fissure
- physiological: pregnancy, old age
- drugs (prolong transit)
What are the external and internal signs of faecal incontinence?
External:
- visibile soiling
- excoriation (scars/defects)
Internal:
- organic disease (piles, fissures, fistula, tumour)
- defects
- tone
- squeeze
- pelvis floor dysnergia
- rectocele/intussusception
What is the difference between passive and urge incontinence?
Passive:
- structural/functional lesion
- internal sphincter
Urge:
- structural/function lesion
- external sphincter
What are the pharmacological treatment options for constipation?
- Stimulants (Senna, bisacodyl)
2. Stool softeners (docusate, lactulose)
