rectum and anal canal Flashcards
where does the rectum start
S3
describe the shape of the rectum
has lateral concavities that form left, right, left rectal folds
the lower part is slightly dilated- the rectal ampulla
the middle concavity on the right is most pronounced
why is the first concavity on the left
because the sigmoid leads to the rectum from the left
what is found next to the rectum
pararectal fossae
what is the pouch of douglas
the rectouterine pouch
describe the peritoneal covering of the rectum
covered by mesorectum which is not a mesentery.
the upper third of the rectum is covered front and sides by peritoneum
the middle third is only covered in front
the lower third has no peritoneal covering
contains sup rectal artery and veins plus lymph nodes and nerves
what is denonvilliers fascia
rectoprostatic fascia in the lower part of the rectovesical pouch
how long is the rectum
12 cm
what are the anterior relations of the rectum
bladder, vas, seminal vesical, prostate, pelvic floor
what nerves are at risk in rectal surgery
urogenital nerves and vessels
describe the internal sphincter
derived from circular smooth muscle, autonomic, ends at the intersphincteric groove
describe the external sphincter
striated muscle, deep, superficial and subcutaneous parts
what muscles surround the anus
puborectalis and pubococcygeus
what muscle forms a sling around the anorectal junction
puborectalis
what is the anococcygeal ligament
formed by the fused levator ani and attaches the anal canal to the coccyx
what does the external sphincter fuse with in the female
puborectalis, anococcygeal ligament and the perineal body
what are the features of the inside of the anus
mucous membrane and submucosa are loose, mobile and distensible
rich underlying vasculature
how is anal closure maintained
anal cushions and internal sphincter
what is the superior rectal artery a branch of
inferior mesenteric
what is the middle rectal artery a branch of
internal iliac- may be absent
what is the inferior rectal artery a branch of
internal pudendal
may also be a contribution from the median sacral which may bleed during surgery
describe the rectoanal veins
mirror arteries
form external and internal venous plexuses which form a portosystemic anastomosis
this is due to sup. rect veins to inf. mesenteric and middle rectal veins going to the internal iliac
what is the lymph drainage of the rectum
inf mesenteric nodes
internal iliac nodes
superficial inguinal nodes for distal anal canal
what is the parasympathetic supply of the rectum
pelvic splanchnics from S2,3,4 Going to the pelvic plexus
what is the function of the pelvic plexus
caries recto anal sensations and controls the internal sphincter
what plexus forms the pelvic plexus
superior hypogastric plexus
what controls the external sphincter and adjacent pelvic flood muscles and gives sensation to the distal anal canal
inferior rectal which is derived from the internal pudendal nerve from S2-4
what happens during defecation
cortical inhibition is released
abdo pressure is increased
puborectalis relaxes, allows the rectal angle to straighten
external sphincter relaxes (s2-4)
lower colon and rectum contract while the internal sphincter relaxes
what might cause incontinence
cord lesions above S2-4
loss of cortical control
damage to external sphincter during surgery
entrapment of the pudendal nerve
what is the ischio anal fossa
fat filled pyramid region below levator ani and either side of the anal canal to allow distension during defecation
where does the pudendal neurovascular bundle lie
laterally in alcock’s canal (obturator fascia)
what does the inferior rectal NVB supply
external sphincter and anal canal sensation
what muscle inserts onto the anococcygeal body
iliococcygeus, pubococcygeus and ishiococcygeus
where is alcocks canal
overlies obturator internus and lateral to the rectum
