Rectum and Anal Canal Flashcards
Rectum location
Sits in curvature of sacrum, retroperitoneal
2 indentations, 1 on R, 2 on L
In the pelvis
Female rectal pouches
Rectouterine pouch, lowest part of peritoneal cavity, back of vagina
Vesiculouterine pouch, top of bladder
Peritoneal coverings of rectum
Upper 1/3, peritoneum on front and sides of rectum
Middle 1/3, peritoneum only on the front
Lower 1/3, no peritoneum
Male rectal pouches
Rectovesicular pouch, between rectum and behind bladder
Anal triangle
Puborectalis muscles wrap around the anus and external anal sphincter, towards sacrum
Muscles here form the pelvic floor
Where is the perineum and what does it cover
Urogenital triangle, the anterior side
Ischioanal fossa structure
Internal smooth sphincter, with external skeletal sphincter around anal canal
Fat filled ischiorectal space under levator ani
Obturator internus next to ischium, internal pudendal artery, vein in pudendal canal
Function of the pudendal nerve
Supplies external anal sphincter
Innervation of the external sphincter and levator ani
Inferior rectal nerve, branch of the pudendal nerve
Anorectal junction
Puborectalis surrounds the anorectal junction, part of the levator ani
Anococcygeal ligament attaches to external anal sphincter muscles and puborectalis, changes angle between rectum and anal junction
Perineal body, anchorage of some muscle fibres
Bones and tendon around the anorectal junction
Pubis symphysis at anterior side
Ischio pubic ramus on anterior side
Ischial tuberosity on corner , attaches to the sacrotuberous ligament on the posterior side
What occurs at rest during defaecation
Rectum follows curve of sacrum
Obtuse anorectal angle
Puborectalis forms sling around rectum
What occurs during straining during defaecation
Rectum becomes straighter
Almost 180 degree anorectal angle
Puborectalis relaxes, pelvis floor descends
Internal structure of the rectum and anal canal Sigmoid Rectum Rectal ampulla Upper anal canal Lower anal canal
Sigmoid, plicae circularis, teniae coli, epiploici
Rectum, coat of longitudinal muscle, 3 plicae folds, form rectal valves
Rectal ampulla, marks end of rectum
Upper anal canal, has folds of mucosa between columns, form anal valves
Pectinate line at bottom upper canal anal
Lower anal canal, pecten
What can you see in a rectal endoscopy
Yellow masses, colon cancer
Polyps can turn cancerous
Anal sphincters
Internal sphincter
External sphincter
Internal sphincter, longitudinal muscle from rectum joins with levator ani muscle (puborectalis) to form the conjoined longitudinal muscle.
Internal anal sphincter from white line upwards
External anal sphincter skeletal fibres under pudendal branch of pudenda nerve, tonic contraction until relaxed
Arterial supply of rectum
IMA, branches into superior rectal artery
Internal iliac, branches into middle rectal artery, supplies hindgut above pelvic floor
Internal pudendal, branches into inferior rectal artery, below pectinate line
Venous drainage of the rectum
Veins match arteries
Superior rectal veins join splenic veins
Internal pudendal vein => internal iliac => common iliac
Formation of haemhorrhoids
Internal
External
Internal, forms in anal sinus, collection of mucosal veins bulge out
External, collection of mucosal veins below pectinate line, proctodeal drainage
Lymphatic drainage
Anal
Middle rectal
Hindgut
Anal, superficial inguinal
Middle rectal, internal iliac
Hindgut, inferior mesenteric => preaortic
Superficial inguinal => external iliac and internal iliac => both join common iliac => para aortic
Neural control of defaecation
Sigmoid colon in mass contraction, moves faces to rectum
Rectal wall stretches, sensed by afferent parasympathetic (pelvic splanchnic and inferior hypogastric)=> S2-S4 => brain
At the same time, somatic afferents from S2-S4 (pudendal) from anal sphincter => spinal cord
Inhibition of sympathetic L1-2 (lumbar splanchnic and inferior hypogastric) to relax involuntary sphincter
Pudendal nerves control somatics, puborectalis => straighten rectum
Transversus abdominus applies anterior pressure
Parasympathetic (pelvic splanchnic and inferior hypogastric), splanchnic nerve, contract smooth sigmoid and rectal muscle
Difference between preaortic and paraaortic lymph nodes
Preaortic
-Drain GI lymphatics
Paraaortic
-Drain pelvic organs
What is the Pectinate line
What is the White line
Pectinate line
-Represents the hindgut proctodeum junction
Hilton’s White line
-Marks transition between internal and external anal sphincter muscles
What is the function of the superior hypogastric plexus
What is the function of the inferior hypogastric plexus
What is the relationship between the 2?
Autonomic pelvic nerves
Superior - sympathetic lumbar and visceral afferents
Anterior to aortic bifurcation
-SNS function of pelvic organs
Branches out into right and left hypogastric
Inferior - formed from pelvic splanchnic branches (PNS) and sacral splanchnic branches (SNS)
-SNS, PNS to pelvic organs
Lateral to rectum, bladder and vagina
