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3002 > 75 Rectum and anal canal > Flashcards

75 Rectum and anal canal Flashcards

1
Q

Function of the rectum?

A

Storage of faeces prior to defecation

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2
Q

What are the rectal concavities?

A
  • Lateral curvatures seen externally
  • Forming left, right, left rectal folds or valves that are seen internally
  • The middle concavity on the right is more pronounced
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3
Q

What are the muscle layers in the rectal wall?

A

Complete longitudinal and circular muscle layers

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4
Q

What is the rectal ampulla?

A

Lower part of rectum which is slightly dilated

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5
Q

Where is the first concavity? Why?

A

On the left and the sigmoid leads to the rectum from the left

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6
Q

What are pararectal fossa?

A

Invaginations of peritoneum on either side of the rectum

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7
Q

Presence of peritoneum on the rectum?

A
  • Upper 1/3: Front and sides
  • Middle 1/3: Front only
  • Lower 1/3: None
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8
Q

Anatomical relations of the rectum?

A

Males:
• Denonvillier’s fascia (retroprostatic fascia)
• Rectovesical pouch

Females:
• Rectouterine pouch (of Douglas)
• Rectovaginal fasciae/ septum

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9
Q

What is the mesorectum?

A
  • Not a mesentery
  • Posteriorly between reflecting peritoneum (mesolectal fascia)
  • Containing rectal artery and vein plus lymph nodes and nerves
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10
Q

How long is the rectum and anal canal?

A
  • Rectum = 12cm

* Anal canal = 4cm

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11
Q

Where is the rectoanal junction?

A

Level of the pelvic floor/ diaphragm (puborectalis posterior to perineal body)

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12
Q

Epithelium changes in the anal canal?

A

Changes from columnar —> stratified squamous —> skin

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13
Q

What is the pectinate line?

A
  • In anal canal where embryological and afferent nerve supply changes
  • Sensitive to pain below line
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14
Q

What structures does the anal canal pass through?

A

Pelvic floor/ diaphragm and ischioanal fossae

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15
Q

Features of the internal anal sphincter?

A
  • Smooth muscle
  • Autonomic
  • Derived from circular muscle layer
  • Ends at intersphincteric groove
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16
Q

Features of external anal sphincter?

A

Striated muscle with deep, superficial and subcutaneous parts

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17
Q

Anatomical position of puborectalis?

A
  • Part of levator ani
  • Forms a sling around the anorectal junction drawing it anteriorly to make a more cute angle
  • Important addition to rectoanal continence
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18
Q

How is the anococcygeal body formed? Attachment?

A
  • Formed by the fused levator ani

* Attaches to the anal canal to the coccyx

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19
Q

What does the external anal sphincter fuse to?

A
  • Puborectalis
  • Transversus perinei
  • Anococcygeal body
  • Perineal body (female)
20
Q

Name the internal features of the anal canal?

A
  • Anal columns
  • Anal valves
  • Pectinate line
  • Anal cushions (3, 7, 11 o’clock)
  • Anal sinuses
  • Anal glands
21
Q

What supplies the anal columns?

A

Terminal branches superior rectal artery and vein

22
Q

Clinical relevance of the risk underlying the rich vasculature of the anal canal?

A

Haemorrhoids or piles

23
Q

Role of anal cushions and internal sphincter?

A

Maintain anal closure when there is no pressure or content from the rectum

24
Q

Describe the mucous membrane and submucosa in the anal canal?

A

Loose, mobile and distensible to allow the expansion for defecation

25
Q

What are the rectoarteries that supply the rectum and anal canal?

A
  • Superior rectal - from inferior mesenteric (usually main supply)
  • Middle rectal - from internal iliac (highly variable and often absent)
  • Inferior rectal - from internal pudendal
  • May be a contribution from the median sacral - cause bleeding during surgery
  • Rectoanal arteries - free anastomosis esp. of superior and inferior rectals
26
Q

What are the rectoanal veins that drain the rectum and anal canal?

A
  • Superior rectal veins - to inferior mesenteric –> portal vein (portal circulation)
  • Middle rectal veins - to internal iliac veins
  • Inferior rectal veins - to internal pudendal veins (systemic circulation)

• Rectoanal veins - form external and internal (submucosal) venous plexus (porto-systemic anastomosis)

27
Q

Rectoanal lymphatic drainage?

A

• Rectoanal lymphatic drainage initially to nodes adjacent to the rectum

  • Inferior mesenteric nodes - for superior part of rectum possible via sacral nodes
  • Internal iliac nodes - for lower rectum and proximal anal canal
  • Superficial inguinal nodes - for distal anal canal
28
Q

Recto-anal nerve supply:

  • Sympathetic?
  • Parasympathetic?
  • Somatic?
A

These nerves carry both afferent (sensory) and efferent (motor) fibres

  • Sympathetic lumbar splanchnics
  • Parasympathetic pelvic splanchnics (from S2, S3, S4) going to pelvic plexus (inferior hypogastric)

• Pudendal nerve (somatic) from S2, S3, S4 giving inferior rectal branches to supply the external anal sphincter, adjacent pelvic floor muscles (puborectalis) and sensation to the distal anal canal

29
Q

What do the pelvic plexuses carry and control?

A
  • Carry rectoanal sensation (faeces vs. flatus)

* Control internal anal sphincter (sympathetic contraction and parasympathetic relaxation

30
Q

Pudendal nerve in pelvis?

A
  • Somatic from S2, S3, S4
  • Giving inferior rectal branches to supply the external anal sphincter, adjacent pelvic floor muscles (puborectalis) and sensation to distal anal canal
31
Q

What divides to form left and right pelvic plexuses?

A

Superior hypogastric

32
Q

Which occurs in normal continence?

A
  1. Levator ani and puborectalis, making rectoanal angle more acute; internal and external anal sphincters; abdominal pressure flattens anterior wall of lower rectum over upper anal canal; anal cushions close the canal
  2. Rectum can partially fill without an increase in pressure; the anal canal sensation (specialised receptors) can allow the cortex to distinguish between gas, fluid and solid faeces; there are stretch receptors in levator ani and the tissue around the anal canal
  3. Eventually, rectal pressure forces its contents into the anal canal, but defecation is prevented by learned cortical inhibition; only gas may be allowed to escape the external anal sphincter forces faeces sac up in to the rectum
33
Q

When is defecation “allowed”?

A
  • Cortical inhibition is released, via the coritcospinal tracts
  • Abdominal pressure is increased
  • Puborectalis relaxes allowing the rectoanal angle to straighten; the external sphincter anal splinter relaxes (somatic S2, S3, S4)
  • The lower colon and rectum contract while the internal anal sphincter relaxes (parasympathetic pelvic splanchnics S2, S3, S4 via pelvic plexus)
  • Reflexes are therefore at S2, S3, S4
34
Q

Causes for bowel incontinence?

A
  • Loss of control following cortical or cord lesions above S2, S3, S4
  • Damage to the external anal sphincter during obstetric or perineal procures
  • Entrapment of the pudendal nerve
35
Q

What occurs at the pectinate line?

A

At the pectinate line in the anal canal the embryo-logical endoderm changes to ectoderm distally

36
Q

Changes in innervation, vascular supply and lymph drainage above and below pectinate line?

A 
Above pectineal line:
• Autonomic (visceral) innervation
• Arteries from inferior mesenteric
• Veins to portal circulation
• Lymph to internal iliac nodes

Below pectineal line:
• Somatic innervation (sensitive to pain)
• Inferior rectal artery from internal pudendal
• Inferior rectal vein to systemic circulation
• Lymph to superficial inguinal nodes

37
Q

What is the anal triangle in between?

A
  • Ischial tuberosities
  • Sacrotuberous ligaments
  • Coccyx
38
Q

What is the ischioanal fossa?

A
  • Fat-filled pyramidal region inferior to levator ani and on either side of the anal canal to allow its distension during defectation
  • May communicate with each other posterior to the anal canal
  • Has a small anterior extension above the deep perineal pouch
  • Site of infections and abscesses that may require surgical intervention
39
Q

What does the perineal membrane span?

A
  • Spans the urogenital triangle between the ischiopubic rami

* Note an anterior aperture for the passage of nerve and vessels to the penis or clitoris

40
Q

Where does the pudendal neurovascular bundle lie?

A

Lies laterally in Alcock’s canal (obturator fascia)

41
Q

Inferior rectal neuromuscular bundle passes across ischioanal fossa to supply ____?

A

External anal sphincter and anal canal sensation

42
Q

What structures form the inferior border of ischioanal fossa?

A

Buttock skin and fat along with gluteus maximus

43
Q

Consequences of dilation of the venous plexuses in ischional fossa and anal canal?

A

Leads to haemorrhoids or piles

44
Q

What causes ischioanal abscesses in the anal canal?

A

Sinus from the anal canal

45
Q

What are the dermatomes that supply the perianal skin?

A

S4, S5

• Maybe important when assessing possible spinal cor or nerve root injury

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