35. Anatomy and Physiology of the Anorectum Flashcards
The GI tract arises from the endoderm. What do the following germ cell layers contribute to later in its development?
a) endoderm
b) mesoderm
c) neural crest
Give the division of, and main artery found in the:
a) foregut
b) midgut
c) hindgut
a) mucosal epithelium, mucosal and submucosal glands
b) lamina propria, muscularis mucosae, submucosal CT, BV, muscularis externa, adventita/serosa
c) neurons and nerves of submucosal and myenteric plexi
a) oesophagus to first 2 sections of duodenum, coeliac artery
b) lower duodenum to first 2/3 of transverse colon, superior meseteric artery
c) last 1/3 of transverse colon to upper part of anal canal, inferior mesenteric artery
What is Hirschsprings disease? What are the symptoms?
What are the 4 main pelvic floor muscles?
Are the IAS and EAS voluntary or involuntary?
Lack of enteric neurons in distal portion of gut (normally derived from neural crest cells). Fail to pass meconium in 48hrs, swollen belly, vomiting bile (green).
Pubococcygeus, puborectalis, iliococcygeus, ischiococcygeus
IAS: involuntary thickened muscle, innervated by enteric NS
EAS: voluntary, thicker muscle, close to anal orifice, innervated by pudendal nerve
Describe the structure of puborectalis.
What makes up most of the pelvic floor?
What nerves are responsible for continence?
What maintains faecal continence?
Striated muscle, passes backward from the back of pubic symphysis to form U-shaped loop that slings rectum to pelvis. Sourrounds rectum, vagina and urethra, supports EAS and assists in creating and maintaining the anorectal angle. (pic)
Levator ani (divided into ischiococcygeaus, iliococcygeus and pubococcygeaus (main part))
S2-S4 parasympathetic = pudendal nerve (from sacral plexus)
IAS, EAS, puborectalis
What do the valves of Houston do in the sigmoid colon?
What is rectal complicance?
Distinguish between resting pressure and squeeze pressure.
What is RAIR?
Provide mechanical barrier and retard stool progression.
Rectum can adapt to imposed stretch to accomodate for contents and delay defecation.
IAS = continuously tonic state = closure of resting presure of anal canal. When stool bolus in anal canal, EAS contributes to anal pressure (squeeze pressure).
Rectoanal inhibitory reflex: involuntary IAS relaxation in response to rectal distension -> some rectal contents descend to anal canal = specialized sensory mucosa detects consistency
What 3 processes does defacation require?
What are the different definitions of constipation?
What is the colonic transit test?
What are the 2 types of incontinence?
What tests can be used to check colonic transit/evacuation/sphincter evaluation?
Relaxation of puborectalis, straightening of anorectal angle, relaxation of EAS
Infrequent stools, hard stools, incomplete evacuation
Capsule containing different shaped markers, XRAY and see where they are. If slow transit, see them in lots of different areas.
Passive (IAS), Urge (EAS)
Colonic transit: radio-opaque markers (above), Evacuation: MRI proctogram, balloon expulsion test, Sphincter evaluation: endoanal US/MRI, anorectal manometry
How might you manage anorectal problems?
Diet, laxatives, biofeedback, transanal irrigation, surgery, psychological therapy, neuromodulation
