Defecation and anal anatomy

Question 1

What is the cause of an imperforate anus/anorectal malformation

Answer 1

• failure of rupture of the anal membrane

- -> failure of communication of the endodermal and ectodermal portions of the anal canal

Question 2

What is persistent cloaca?

Answer 2

• 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

Question 3

What is Hirschsprung’s disease?

Answer 3

• 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)

Question 4

What are the symptoms of Hirschsprung’s disease?

Answer 4

• failing to pass meconium within 48 hours
• swollen belly
• vomiting bile (will appear green)

Question 5

How is Hirschsprung’s disease treated?

Answer 5

surgical resection fo the aganglionic part of the colon

Question 6

Compare the external and internal anal sphincter.

Answer 6

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

Question 7

What nerves are responsible for continence?

Answer 7

Pudendal nerve (S2-S4 parasympathetic supply)

Question 8

What are the S+S of constipation?

Answer 8

• infrequent stools (<3 per week)
• passage of hard stools (>25% of the time)
• sensation of incomplete evacuation (>25% of the time)

Question 9

Explain continence in terms of defecation?

Answer 9

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

Question 10

What tests can be done to check colonic transit?

Answer 10

• radio-opaque/transit xray

- colonic scintigraphy

Question 11

What tests can be done to check evacuation?

Answer 11

• MRI proctogram
• barium proctogram
• balloon expulsion test

Question 12

What tests can be done to evaluate the sphincter?

Answer 12

• endoanal ultrasound
• endoanal MRI
• anorectal manometry

Question 13

Compare hypersensitive and hyposensitive rectal sensation.

Answer 13

Hypersensitive:

• reduced sensory threshold to volumetric rectal distension
• bowel disorder, IDK, intussusception

Hyposensitive:
- increased sensory threshold to volumetric recta distension

Question 14

What is normal transit constipation?

Answer 14

• 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

Question 15

What is slow transit constipation?

Answer 15

• common in young women and children
• infrequency and slow movement of stool
• bloating, abdominal pain and infrequent urger to defecate

Question 16

What is rectal evacuatory disorder?

Answer 16

• common in children
• associated with hard/painful stools, per rectal bleeding
• bloating, abdominal pain and infrequent urge to defecate

Question 17

Why does rectal prolapse usually occur?

Answer 17

• 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

Question 18

What is rectal intussusception?

Answer 18

• telescoping of the rectum into itself during training

- cna cause an obstruction on defecation

Question 19

What is defecation dysnergia?

Answer 19

• dysfunction of the pelvis floor and anal sphincters

- inability to coordinate the abdominal and pelvic floor muscles to evacuate stools

Question 20

What are the secondary causes of constipation?

Answer 20

1. endocrine: diabetes, hypothyroidism
2. neurological: spinal injury, Parkinson’s disease
3. psychogenic: affective disorders, eating disorders
4. metabolic
5. colonic: tumour, diverticular disease
6. anal: fissure
7. physiological: pregnancy, old age
   - drugs (prolong transit)

Question 21

What are the external and internal signs of faecal incontinence?

Answer 21

External:

• visibile soiling
• excoriation (scars/defects)

Internal:

• organic disease (piles, fissures, fistula, tumour)
• defects
• tone
• squeeze
• pelvis floor dysnergia
• rectocele/intussusception

Question 22

What is the difference between passive and urge incontinence?

Answer 22

Passive:

• structural/functional lesion
• internal sphincter

Urge:

• structural/function lesion
• external sphincter

Question 23

What are the pharmacological treatment options for constipation?

Answer 23

1. Stimulants (Senna, bisacodyl)

2. Stool softeners (docusate, lactulose)