Clinical Anatomy of Faecal Continence - the Distal GI Tract

Question 1

What does control of faeces excretion require?

Answer 1

Holding area (rectum) - stores faeces
Visceral afferents - senses fullness of rectum
Functioning muscle sphincters - appropriately contract and relax
Normal cerebral function

Question 2

What can affect control of faeces exertion?

Answer 2

Medications
Age-degeneration
Consistency of stool

Question 3

What are the borders of the pelvic cavity?

Answer 3

Pelvic inlet and pelvic floor

Question 4

At what level does the sigmoid colon become the rectum?

Answer 4

S3

Question 5

The rectum lies in the pelvis/perineum and the anal canal & anus lie in the pelvis/perineum

Answer 5

Pelvis

Perineum

Question 6

Give some of the anatomical relationships of the rectum

Answer 6

Peritoneum covers the superior rectum
Rectouterine/rectovesical pouches lie anterior to the superior rectum
Prostate gland lies anterior to the inferior rectum
Vagina and cervix lie anterior to the inferior rectum

Question 7

What three sets of muscle fibres form the levator ani?

Answer 7

Puborectalis
Pubococcygeus
Iliococcygeus

Question 8

Describe the levator ani muscle

Answer 8

Forms most of the floor of the pelvis and roof of the perineum
Skeletal muscle
Tonically contracted most of the time

Question 9

What is the nerve supply to the levator ani?

Answer 9

Nerve to levator ani (branch of sacral plexus)
Pudendal nerve (S2-S4)

Question 10

Describe the muscle, area covered, nerve supply and contraction status of the two anal sphincters

Answer 10

Internal anal sphincter - smooth muscle covering the superior two thirds of the anal canal, contraction stimulated by sympathetic fibres and inhibited by parasympathetics. Contracted all the time, relaxes reflexively
External anal sphincter - skeletal muscle covering the inferior two thirds of anal canal, contraction stimulated by pudendal nerves and is voluntarily contracted

Question 11

Describe the nerve supply to structures in the pelvis and perineum

Answer 11

Pelvis - in the body cavity therefore structures are supplied by autonomics
Perineum - in the body wall therefore structures are supplied by somatics

Question 12

Describe the sympathetic supply to the rectum/anal canal

Answer 12

Sympathetic fibres travel from T12-L2 to inferior mesenteric ganglia, then travel via periarterial plexuses around branches of the IMA
Important in:
Contracting internal anal sphincter
Inhibiting peristalsis

Question 13

Describe the somatic motor supply to the rectum/anal canal

Answer 13

Somatic motor fibres come from the pudendal nerve and nerve to levator ani.
Important in contracting external anal sphincter

Question 14

Describe the parasympathetic supply to the rectum/anal canal

Answer 14

Parasympathetic fibres run from S2-S4 via pelvic splanchnic nerves and synapse in walls of rectum
Important in:
Inhibiting contraction of internal anal sphincter
Stimulating peristalsis

Question 15

Describe visceral afferent supply to the rectum/anal canal

Answer 15

Visceral afferents run with parasympathetic fibres back to S2-S4
Important in sensing stretch, ischaemia etc.

Question 16

Outline the route of the pudendal nerve

Answer 16

Exits pelvis via greater sciatic foramen → Quickly enters pelvis via lesser sciatic foramen → Branches to supply structures of perineum

Question 17

How does labour affect the pudenal nerve and any nearby muscle fibres?

Answer 17

Labour may cause the branches of the pudendal nerve to be stretched
It may cause fibres of the puborectalis or external anal sphincter to be torn

Question 18

What is the pectinate line?

Answer 18

The junction between the part of the embryo that formed the GI tract and the part that formed the skin

Question 19

What is the difference in nerve supply above and below the pectinate line?

Answer 19

Above - nerve supply is autonomic

Below - nerve supply is somatic

Question 20

What is the difference in arterial supply above and below the pectinate line?

Answer 20

Above - arterial supply is from IMA

Below - arterial supply is from internal iliac artery

Question 21

What is the difference in venous drainage above and below the pectinate line?

Answer 21

Above - venous drainage via IMV

Below - venous drainage is via internal iliac veins

Question 22

What is the difference in lymphatic drainage above and below the pectinate line?

Answer 22

Above - lymph drains to inferior mesenteric nodes

Below - lymph drains to superficial inguinal nodes

Question 23

Describe the lymphatics of the pelvis

Answer 23

Lymph vessels of pelvis run alongside respective arteries. Main lymph nodes are:
Internal iliac (drains inferior pelvis)
External iliac (drains lower limb and more superior pelvic structures)
Common iliac (drains lymph from internal and external iliacs)
Lumbar (drains lymph from common iliacs)

Question 24

What are the differences between rectal varices and haemorrhoids?

Answer 24

Rectal varices - caused by portal hypertension and a dilatation of collateral portal and caval veins
Haemorrhoids - not related to portal hypertension - are a prolapse of rectal venous plexuses

Question 25

What are ischioanal fossae?

Answer 25

These are fossae that lie on each side of the anal canal and are filled with fat and loose connective tissue