Rectum, anal canal & ischiorectal fossae

Question 1

What is the cloaca? Why is it relevant to the rectum/anal canal?

Answer 1

Cloaca is the terminal end of the hindgut before division into faecal, urinary and genital outflow tracts

Question 2

What divides the genitals from the rectum in the developing fetus?

Answer 2

the urorectal septum

Question 3

The anal membrane divides what two tissues?

Answer 3

the anal membrane divides ectoderm and endoderm (no mesoderm present)

Question 4

What are the posterior branches off the internal iliac artery?

Answer 4

iliolumbar artery

lateral sacral artery

superior gluteal artery

* same in the male/female*

Question 5

What are the anterior branches of the internal iliac?

Answer 5

parietal

• obturatory
• inferior gluteal
• internal pudendal

Visceral

• umbiliacal
• inferior vesical/uterine in women
• middle rectal
• vaginal (in women)

Question 6

What are the muscles making up the pelvic floor?

Answer 6

pubococcygeus

iliococcygeus

ischiococcygeus

puborectalis

Question 7

What muscle maintains the angle of the anal canal?

Answer 7

the puborectalis (very importance for anal continence)

Question 8

What nerve supplies the anal sphincter?

Answer 8

pudendal nerve (S2,3,4)

Question 9

What are the pouches infront of and behind the uterus?

Answer 9

uterovescial space and the pouch of douglas

Question 10

What pouch sits infront of the rectum in the male pelvis?

Answer 10

the rectovesical pouch

Question 11

What fascia prevents local spread of cancer from the prostate gland?

Answer 11

Denonvillier’s fascia - sits behind the bladder and prostate gland - between the prostate and the rectum

Question 12

What lobe of the prostate is palpated from the rectom?

Answer 12

lateral lobes

Question 13

how is the rectum divided?

Answer 13

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

Question 14

What is the blood supply to the anus/rectum?

Answer 14

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

Question 15

What vertebral level does the rectum start at?

Answer 15

Starts at S3

Question 16

What are the rectal ‘valves’ referred to as?

Answer 16

They are the ‘valves of houston’ - they have no obvious purpose

Question 17

What is the lower end of the rectum called?

Answer 17

the ‘Ampulla’

Question 18

What event causes relaxation of the sphincters?

Answer 18

the dilation of the rectal ampulla

Question 19

Does the rectum have appendices epiplociae? Does it have taeniae?

Answer 19

No, neither

Question 20

What are the borders of the rectum?

Answer 20

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)

Question 21

The anal canal is composed of what two types of cells?

Answer 21

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

Question 22

What divides the two regions of the anal canal?

Answer 22

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.

Question 23

What is the anocutaneous line?

Answer 23

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.

Question 24

differentiate the upper and lower halves of the anal canal

Answer 24

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.

*

Question 25

Where might infection occur from the anal canal?

Answer 25

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.

Question 26

What is the ischio rectal fossa? What does it contain? What is it’s purpose?

Answer 26

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

Question 27

What is the alcock’s canal?

Answer 27

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

Question 28

Describe the muscle/fascia layers that make up the anal sphincters

Answer 28

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