Rectum, anal canal & ischiorectal fossae Flashcards
What is the cloaca? Why is it relevant to the rectum/anal canal?
Cloaca is the terminal end of the hindgut before division into faecal, urinary and genital outflow tracts
What divides the genitals from the rectum in the developing fetus?
the urorectal septum
The anal membrane divides what two tissues?
the anal membrane divides ectoderm and endoderm (no mesoderm present)
What are the posterior branches off the internal iliac artery?
iliolumbar artery
lateral sacral artery
superior gluteal artery
* same in the male/female*
What are the anterior branches of the internal iliac?
parietal
- obturatory
- inferior gluteal
- internal pudendal
Visceral
- umbiliacal
- inferior vesical/uterine in women
- middle rectal
- vaginal (in women)
What are the muscles making up the pelvic floor?
pubococcygeus
iliococcygeus
ischiococcygeus
puborectalis
What muscle maintains the angle of the anal canal?
the puborectalis (very importance for anal continence)
What nerve supplies the anal sphincter?
pudendal nerve (S2,3,4)
What are the pouches infront of and behind the uterus?
uterovescial space and the pouch of douglas
What pouch sits infront of the rectum in the male pelvis?
the rectovesical pouch
What fascia prevents local spread of cancer from the prostate gland?
Denonvillier’s fascia - sits behind the bladder and prostate gland - between the prostate and the rectum
What lobe of the prostate is palpated from the rectom?
lateral lobes
how is the rectum divided?
It is divided into thirds based on the peritoneal covering
the superior third is covered completely by peritoneum, the middle third is only covered antiorly
the inferior third and into the anal canal is completely free from peritoneum
What is the blood supply to the anus/rectum?
inferior mesenteric artery (branches off anterior aorta at L3) - gives the superior rectal and the middle rectal
Veins = inferior mesenteric to portal and middle rectal
What vertebral level does the rectum start at?
Starts at S3
What are the rectal ‘valves’ referred to as?
They are the ‘valves of houston’ - they have no obvious purpose
What is the lower end of the rectum called?
the ‘Ampulla’
What event causes relaxation of the sphincters?
the dilation of the rectal ampulla
Does the rectum have appendices epiplociae? Does it have taeniae?
No, neither
What are the borders of the rectum?
Posterior
- sacrum/coccyx
- rectal vessels and lyphatics
- Waldeyer’s fascia
Laterally
- fascia - distensible
- supported by levator ani
Anteriorly
- upper 2/3 peritoneum
- coils of small bowel
- pouch of Douglas (rectouterine or rectovesical pouch in men)
Below pouch
- Denonviller’s Fascia (prevents spread of prostatic cancer)
The anal canal is composed of what two types of cells?
Squamus and columnar - Squamus cells come from ectoderm - they are in the most distal region- they are more durable cells
Columnar cells are more proximal in the anal canal - they come from endoderm and present more vague pain
What divides the two regions of the anal canal?
The pectinate line (dentate line) is a line which divides the upper two thirds and lower third of the anal canal. Developmentally, this line represents the hindgut-proctodeum junction.
What is the anocutaneous line?
inferior border of the anal pecten (non keratinised sqaumous epithelium) where the stratified squamous epithelium changes from the hairless anoderm to typical (hairy) skin; commonly coincides with the inferior border of the internal anal sphincter.
differentiate the upper and lower halves of the anal canal
Upper half of anal canal:
- The mucous membrane derived from hindgut endoderm
- It is lined by simple columnar epithelium
- It has vertical folds called anal columns of morgagni that are joined together at their lower ends by semilunar folds called anal valves= openings for glands
- Arterial supply is through the superior rectal artery, which is a branch of the inferior mesenteric artery. It is good to remember that the inferior mesenteric artery also supplies terminal parts of the large intestine
- Venous drainage is by way superior rectal vein, which is a tributary of the inferior mesenteric vein.
- Lymph drainage: The lymphatics pass upward along the inferior rectal artery to the pararectal nodes and eventually into the inferior mesenteric nodes.
- Upper half is visceral sensory innervation = autonomic
Lower half of anal canal:
- The mucous membrane is derived from ectoderm
- lined by stratified squamous epithelium
- There are no anal columns or anal valves
- Arterial supply is through the inferior rectal artery, which is a branch of the internal pudendal artery.
- Venous drainage is by way of inferior rectal vein, a tributary of the internal pudendal vein.
- Lymph drainage: inguinal lymph nodes
- Lower half is innervated by the somatic nerves of pudendal = sensitive to pressure, touch, temp etc.
*
Where might infection occur from the anal canal?
If the mucosa is cut- an infection may develop which could spread into the surround area forming abscesses
Because the ischio rectal space is continuous anteriorly, infection can travel towards the genitals.
What is the ischio rectal fossa? What does it contain? What is it’s purpose?
The ischio rectal fossa laterall is covered by ischium and obeterator internus with the sacrotuberous ligament
medially it touches the levator ani muscles
it contains fat and allows for the expansion of the anal canal - nerves and vessels also pass through it
What is the alcock’s canal?
The pudendal canal (also called Alcock’s canal) is an anatomical structure in the pelvis through which the internal pudendal artery, internal pudendal veins, and the pudendal nerve pass.
Runs along obturator internus
Describe the muscle/fascia layers that make up the anal sphincters
Internal sphincter - continuation of circular muscle of bowel- longitudinal muscle becomes fascia
External sphincter- 3 parts continuous- pudendal nerve supply - subcutaneous layer puckers the anal skin, superficial layer attaches to the perineal body and coccyx (level with internal sphincter), deep layer fuses with puborectalis at sides and back
