Rectum and Anal Canal

Question 1

Describe features of the rectum

Answer 1

• Rectosigmoidal junction at S3,
• Pararectal fossa on both sides,
• Lower part is expanded to form rectal ampulla,
• Lacks taenia, haustra or epiploic,
• Storage of faeces prior to defecation

Question 2

What is the mesorectum

Answer 2

Perirectal fat that surrounds the rectum and is not anatomical term

Question 3

What do the rectal folds result in?

Answer 3

Formation of 3 lateral flexures; on the left it has the superior and inferior and then on the right it has the intermediate

Question 4

What is the perineal flexure?

Answer 4

(anorectal junction) It is the junction between the rectum and the anal canal. It is caused by the anterior pull of the rectum by puborectal muscle

Question 5

What are the anterior anatomical relations of the rectum in the female?

Answer 5

• Rectouterine pouch,
• Sigmoidal colon,
• Ileum,
• Vagina,
• Cervix

Question 6

What are the anterior anatomical relations of the rectum in the male?

Answer 6

• Rectovesicle pouch,
• Sigmoid colon,
• Ileum,
• Bladder,
• Prostate,
• Seminal vesicles

Question 7

What are the posterior relations of the rectum (same in both sex)

Answer 7

• Sacrum and coccyx,
• Piriformis,
• Coccygeus,
• Levator ani,
• Sacral plexus.

Question 8

What is the anal canal?

Answer 8

Terminal part of the digestive tract which is approximately 4cm long. It is a conduit to the outside world

Question 9

What is the anal canal surrounded by?

Answer 9

Levator ani (puborectalis sling), external and internal anal sphincters

Question 10

What is the anorectal ring and its clinical significance?

Answer 10

Muscular structure at the junction of the anal canal and the rectum. Division of this ring results in incontinence

Question 11

Describe features of internal and external anal sphincters

Answer 11

Internal - Smooth muscle which is derived from circular muscle layer and ends at the intersphincteric groove.
External - Striated muscle (S2,3,4 keeps poo off the floor) and one functional unit with deep, superficial and subcutaenous parts. Fuses with puborectalis

Question 12

What is found in the upper part of the anal canal?

Answer 12

8-10 longitudinal folds called anal columns which unit inferiorly to form anal valves, together these form a circle called the pectinate (dentate) line

Question 13

What is superior to each anal valve?

Answer 13

A depression termed anal sinus (crypt) which contains mucousal glands to lubricate faeces.

Question 14

Describe what is above and below the pectinate line?

Answer 14

Above - hemorrhoidal zone,
Inferior - Anal pecten which is sensitive to pain, temp, touch and pressure. It ends inferiorly as the anocutaneous line (where anal canal becomes true skin)

Question 15

What is the arterial supply of the rectum and anal canal?

Answer 15

Superior 1/3 - Superior rectal artery (branch of inferior mesenteric)

Middle 1/3rd - middle rectal artery (branch of internal iliac)

Belowe anorectal line - inferior rectal artery from internal pudendal and branch of superior rectal

Question 16

What is the venous drainage of the rectum and anal canal

Answer 16

• The internal rectal plexus found in the submucosa, it drains to superior and inferior rectal veins.
• External venous plexus between muscle layers; superior 1/3rd to superior rectal then inferior mesenteric then hepatic portal. Middle 1/3rs to middle rectal, to internal iliac and internal pudendal. Inferior 1/3rd to inferior rectal and then to internal iliac and internal pudendal

Question 17

What occurs when there is dilation of anal cushions?

Answer 17

Haemorrhoids

Question 18

What is the lymphatic drainage of the rectum and anal canal?

Answer 18

Superior rectum - Inferior mesenteric nodes,
Inferior rectum and prox anal canal - internal iliac nodes.
Distal anal canal - superficial inguinal nodes

Question 19

What is the parasympathetic supply of the rectum and anal canal?

Answer 19

From S2-4 via pelvic splanchnic nerves (pelvix plexus) They increase peristalsis, relac anal sphincter and visceral senses

Question 20

What is the sympathetic supply of the rectum and anal canal?

Answer 20

From L1-2(3) via lumbar splanchnic nerves, they contract anal sphincter

Question 21

What is the somatic supply of the rectum and anal canal?

Answer 21

From S2-4 via pudendal nerve, it supplies the external anal sphincter and adjacent pelvic floor muscles (below pectinate line)

Question 22

How does faecal continence occur?

Answer 22

Rectum can partially fill without increase in pressure and the anal canal sensation can allow cortex to distinguish between gas, fluid and solid faeces. Eventually rectal pressure forces contents into the anal canal but defecation is prevented by learned cortical inhibition and only gas mat be allowed to escape. The external anal sphincter forces faeces back up.

Question 23

What occurs when we choose to allow defication?

Answer 23

Cortical inhibition is released via corticospinal tracts, abdo pressure increases, puborectalis relaxes allowing rectoanal angle to straighten and the external anal sphincter relaxes. PSNS causes lower colon and rectum to contract while internal anal sphincter relaxes (reflexes at S2,3,4)

Question 24

What occurs in faecal incontinence?

Answer 24

Loss of control following cortical or cord lesions above S2, S3, S4 or damage to external anal sphincter during obstetric or perineal procedures or entrapment of pudendal nerve