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Muscles of levator ani
- medial: pubococcygeus, ileococcygeus
- lateral: ischiococcygeus or coccygeus, rudimentary
- The pubococcygeus is further subdivided to include the puborectalis
- ischial spine and post obturator f
- s3, s4 coccyx
- anococcygeal raphe
- post pubis, ant obturator f
- s4, coccyx
- crisscross anococcygeal raphe
- levator hiatus
- anorectal ring
- anorectal angle
M of sidewalls of pelvis
- obturator internus
- allow pelvic infection to track to extrapelvic spaces (i.e. deep postanal space to ischiorectal fossa)
- superficial and deep transverse perinei muscles
- ventral extension of the external sphincter muscle
- bulbocavernosus t muscle
The postanal plate
- presacral fascia,
- anococcygeal ligament
- anococcygeal raphe (midline condensation of the ileococcygeus)
- dorsal extension of the puborectalis and external anal sphincter fibers to the coccyx.
levator ani innervation
Def: anal canal
- clinical: anal verge to top of anorectal ring
- anatomical: anal verge to dentate line (proctodeal membrane)
- histological: anal verge to 1 cm above anal valves
- involuntary smooth muscle
- 55% RP (10% myogenic, 45% sympathetic)
IAS symp innervation
- hypogastric and pelvic plexus
IAS Parasympathetic innervation is from
S1, S2, and S3 via the pelvic plexus.
- nonadrenergic,noncholinergic pelvic nerves
- Spinal anesthesia decreases rectal tone by 50%
- decreased resting tone seen in diabetic patients may be due to an autonomic neuropathy
slow waves (6-20x/min)
- Ultraslow waves
- less than 3 times a minute
- not present in all individuals.
- associated with higher resting pressures, hemorrhoids and anal fissures.
- outer longitudinal layer and fiber of levators
- shortening and widening of anal canal during defecation
- eversion of anal orifice
- contain sepsis
- septation of thrombosed hemorrhoids (so incise elliptically)
- anococcygeal ligament attaches it to coccyx
- type I
- 30-60 second voluntary contraction in response to distension of rectum
inferior rectal branch of pudendal nerve
anal canal sensation
inferior rectal branch of the pudendal nerve that arises from S2, S3 and S4.
inferior rectal nerve
- first branch of pudendal which arises from
- the internal iliac artery.
- arises alcocks
- second branch of pudendal
- arises alcocks
- inferior rectal:first branch of pudendalarises alcocks
- perineal: second branch
- arises in alcocks
- continues as the dorsal nerve of the penis or clitoris.
parasympathetic system via the pelvic plexus to S2, S3 and S4.
SHA (superior rectal artery)
- continuation of the inferior mesenteric artery
- crosses left illiac
- branches into right and left branches (80%)
- multiple branches (17%)
- terminate into capillary plexuses (RA, RP, LL)
middle rectal artery
- branch of the anterior division of the internal iliac artery or pudendal
- lateral ligaments posterolateral, MHA enters rectum anterolaterally
- injured in anterolateral dissection of rectum
- branch of internal pudendal which is branch of IIA
- rises in pudendal canal
- entirely extrapelvic course
- ligate in APR
- dec supply to posterior commissure
point where the stratified squamous epithelium becomes true skin marked by the presence of hair follicles and sweat glands.
zone between the dentate line and the anal verge.
venous drainage of rectum
superior hemorrhoidal veins draining into the portal venous system (by way of the nferior mesenteric vein) and the middle and inferior hemorrhoidal veins draining into the caval system (by way of the internal iliac veins).
When contracted the puborectalis muscle creates a 90 degree angle between the anal canal and the rectum
relaxation allows the anorectal angle to approach 180 degrees allows defecation.