COLON, RECTUM & ANUS Flashcards
What are the components of continence?
- involuntary - internal anal sphincter
- voluntary - external anal sphincter
- anorectal angle - puborectalis
- anal cushions and mucosal folds
Where does the rectum start and end and what are the peritoneal relations?
starts = S3
ends = puborectalis
12 cm long
peritoneal relations
- upper third = peritoneum on front/sides
- middle third = front only
- lower third = below peritoneum (no peritoneum)
What is the blood supply and nodal drainage for the rectum?
arteries
- superior rectal = IMA
- middle rectal = internal iliac
- inferior rectal = internal pudendal
Nodal drainage
follows arterial supply, therefore
- superior = para-aortic
- middle = internal iliac
- inferior = inguinal
What is the difference between the upper and lower parts of the anal canal?
Anal canal = 4 cm
Divided into upper and lower parts by dentate line
Upper
- endoderm
- columnar cells
- supplied by superior rectal
- drains to para-aortic
- autonomic nerves
Lower
- ectoderm
- squamous
- supplied by inferior rectal
- drains to inguinal
- somatic nerves
What are the differences between the internal and external anal sphincters?
External anal sphincter
- under voluntary control
- has 3 components
- deep = blends with puborectalis
- superficial = attached to two bodies (perineal and anococcygeal)
- subcutaneous
- innervation is via inferior rectal nerve (branch of pudendal nerve) and from perineal branch of S4 nerve.
Internal anal sphincter
- under involuntary control
- under tonic control
- continuation of circular muscle
- Sympathetic fibers from the superior rectal and hypogastric plexuses stimulate and maintain internal anal sphincter contraction.
- Its contraction is inhibited by parasympathetic fiber stimulation.
What are the sites where the hypogastric plexus is at risk of being damaged in colorectal surgery?
- Ligation of IMA: the pre-aortic sympathetic fibres may be damaged.
- Mobilisation of the sigmoid mesocolon: the superior hypogastric plexus at risk.
- Posterior rectal mobilisation if the mesorectal plane is not respected: the inferior hypogastric plexus and pelvic splanchnic nerves at risk.
- Anterior rectum dissection from the seminal vesicles: terminal branches of the pelvic plexus at risk
What are the consequences of damaging the nerves in the hypogastric plexus?
Damage to Pelvic plexus
- erectile dysfunction
- urinary retention
Damage to SNS
- ejaculatory failure
- retrograde ejaculation
What are the variations to the right colic artery?
- 50% of cases = absent
- 30% = arises from middle colic
- 20% = arises from SMA
If the right colic artery is absent, then how does the ascending colon recieve its blood supply?
- superior colic branch of ileocolic
- middle colic from left
What are the variations in the middle colic artery?
- 60% = classic (right and left branches). Arises from SMA
- 40% = additional (second) left sided branch of middle colic either from middle colic or from SMA directly
- minority = MCA absent and transverse colon supplied by left colic artery.
Where is the marginal artery most likely to be absent?
between the ascending branch of the ileocolic and the descending branch of whichever artery is supplying the hepatic flexure and ascending colon.
Occurs in 5% of cases
What is the blood supply to the ureters?
Abdominal ureter
- Renal
- gonadal
Pelvic ureter
- Internal iliac
- vesical
- Middle rectal
What are the posterior relations of the ureter?
- psoas
- genitofemoral nerve
- common iliac artery bifurcation
- sacroiliac joint
What are the anterior relations of the ureter?
Depends on which side
Right side
- duodenum
- gonadal vessel
- right colic artery
- ileocolic
- SMA
Left side
- gonadal vessel
- left colic
- sigmoid mesentry
Male
- Vas
Female
- uterine artery
What is the nerve supply to the ureters?
- inferior mesenteric
- spermatic and pelvic plexuses (autonomic).
