Defecation Flashcards
When does primitive gut tube develop?
After 2 weeks
After 3 weeks
After 4 weeks
After 5 weeks
When does primitive gut tube develop?
After 2 weeks
After 3 weeks
After 4 weeks
After 5 weeks
Microbrial colonisation of the infant is critical for what two things in the adult? [2]
Immune system
GI Development
Name the anal sphincters [2]
Which is voluntary / involuntary?
External Anal Sphincter (EAS): voluntary
Internal Anal Sphincter (IAS): involuntary and thickened muscle
Name the 3 levator ani muscles of the pelvic floor muscles
PPI
Puborectalis
Puboccygeus
Iliococcygeus
Which muscle is depicted?
Puborectalis
Pubcoccygeus
Iliococcygeus
Which muscle is depicted?
Puborectalis
Pubcoccygeus
Iliococcygeus
Which muscle is depicted?
Puborectalis
Pubcoccygeus
Iliococcygeus
Which muscle is depicted?
Puborectalis
Pubcoccygeus
Iliococcygeus
Which muscle is depicted?
Puborectalis
Pubcoccygeus
Iliococcygeus
Which muscle is depicted?
Puborectalis
Pubcoccygeus
Iliococcygeus
What is the role of the puborectalis?
Supports EAS and helps to create the anorectal angle
Surrounds tthe rectum, vagina and urethra
Which nerves provides the parasympathetic innervation to the rectum, anus, bladder and urethrea? [1]
What are the nerve roots? [1]
Pudendal nerve
S2-4
S2, 3, 4 keeps the Penis, Poo and Pee of the floor
The EAS is supplied by which nerve?
The IAS is innervated by which NS?
- What are sympathetic and parasympathetic nerve roots?
EAS: supplied by inferior branch of the pudendal nerve
IAS: Enteric NS
- Sympathetic: L1-L2 via hypogastric nerves (excitatory)
- Parasympathetic: S2-S4: pelvic nerves (inhibitory)
The inferior rectal nerves divides into which two terminal branches? (m v f)
M: Perineal nerve and dorsal nerve of the penis
F: Dorsal nerve of the clitoris
The inferior rectal nerves divides into which two terminal branches? (m v f)
M: Perineal nerve and dorsal nerve of the penis
F: Dorsal nerve of the clitoris
What factors do we rely on for continence? [5]
Anorectal angle
Stool consistency and colonic transit time
Rectal compliance
Rectal filling – sensation
Rectoanal inhibitory reflex (RAIR)
How does the anorectal angle work?
The tonic contraction produced by the puborectalis muscle, creates what is called a ‘flap valve’
Maintains the angle, whereby the anterior rectal wall is pushed downwards onto the anal canal when the intra-abdominal pressure during straining, laughing and coughing rises, thus stopping the passage of faeces into the anal canal
Stool consistency:
Ability of the rectum to retain stool is known as []?
Which two structures provide a mechanical barrier and retard progression of stool? [2]
Ability of the rectum to retain stool is known as reservoir continence
Lateral angulations in the sigmoid colon AND the valves of Houston provide a mechanical barrier and retard progression of stool.
It is the weight of the stool that tends to accentuate these angles and thus enhance their barrier effect
Which structure does this describe?
semi-lunar transverse folds of the rectal wall that protrude into the anal canal
valves of Houston
What is rectal compliance? [1]
Explain how rectal compliance helps continence [1]
Rectal compliance: the ability of the rectum to adapt to the imposed stretch is called
Extrinsic afferent neurones mediate the conscious sensation of urgency which is activated by mechanoreceptors.
Got to be full, have to know that it is full
Explain what the rectoanal inhibitory reflex (RAIR) is
RAIR: a relaxation response in the IAS following rectal distension. Increase in pressure causes the relaxation !
Out of the EAS & IAS, which is responsible for greater anal resting pressure? [1]
Why is that clincically significant? [1]
IAS has higher resting pressures: causes incontinence to not occur
Defaction involves the relaxation of which two muscles? [2]
EAS and puborectalis muscles
Explain proper mechanism for defecation xx
Hold breath forcibly trying to exhaled: causes increase in abdo pressure & muscles of the the anterior abdo wall tense to funnel the pressure down to pelvis; Valsalva manoeuvre
Relaxation leads to stool enter lower rectum
Explain proper mechanism for defecation xx
Hold breath forcibly trying to exhaled: causes increase in abdo pressure & muscles of the the anterior abdo wall tense to funnel the pressure down to pelvis; Valsalva manoeuvre)
Relaxation leads to stool enter lower rectum
Explain how the closing reflex occurs
Last bolus of stool is passed and then the ‘closing reflex’ of the EAS is stimulated by the releases of traction.
Upon voiding, receptor adaptation in ampulla recti removes inhibitory drive to IAS - thus contraction of IAS
Voluntary contraction of EAS closes anus off.
Smooth muscles in sigmoid relax (enteric nervous system) re-establishing of reservoir function.
How do you take Hx for constipation? [8]
- stool frequency and consistency (Bristol Scale)
- need to strain or digitally extract stool – defecatory disorder
- Any clear precipitants to onset? abdominal/pelvic surgery; childbirth or emotional trauma
- Faecal impaction and faecal soiling: suggest idiopathic megacolon
- Comorbid medical history: e.g. thyroid disease, diabetes; renal impairment; neurogenic conditions
- Drug history: e.g. opiates
- Dietary history: meal frequency and fibre intake
- Toilet behaviour – sitting properly, routine
