Anal canal Flashcards
Where does the anal canal run from and to
From the rectal ampulla to the anus
What does the anal canal run between (Anteroposteriorly)
Anococcygeal ligament (posterior) and the perineal body (anterior)
What is the anal canal located within
The anal triangle of the perineum
Length of the anal canal
4cm
What direction does the anal canal follow
Posteroinferior
What surrounds the anal canal and what is there function
Internal and external anal sphincters
They maintain faecal continence
Which anal sphincters are voluntary and involuntary muscle
External is voluntary
Internal is involuntary
Where is the internal anal sphincter
Surrounds the upper 2/3 of the anal canal
Where is the external anal sphincter
Surrounds the lower 2/3 of the anal canal
What does the external anal sphincter blend with
Puborectalis muscle
What must occur to allow defecation
Relaxation of both anal sphincters
What is at the anorectal junction
Anorectal ring (muscular ring formed by fusion of the internal anal sphincter, external anal sphincter and puborectalis muscle)
What are anal canals
Series of longitudinal ridges in the superior aspect of the mucous membrane
What do anal columns contain
Terminal branches of the superior rectal vessels
What joins the anal columns inferiorly
Anal valves
What’s superior to the anal valves and what do they contain
Anal sinuses which contain glands that secrete mucus
When do anal sinuses secrete mucus
When compressed by faeces to aid defecation
What do the anal valves form
The pectinate line
Embryological origin above and below the pectinate line
Above - hindgut
Below - ectoderm of the proctodeum
Epithelial lining above and below the pectinate line
Above - columnar
Below - non keratinised stratified squamous which transitions to keratinised (I.e skin) at the inter-sphincteric groove
How does the anal canal superior to the pectinate line differ from the anal canal inferior to the pectinate line
Blood supply
Innervation
Lymphatic drainage
Embryological origin
Arterial supply above the pectinate line
Aorta -> IMA -> Superior rectal artery
Arterial supply below the pectinate line
Aorta -> common iliac -> internal iliac -> internal pudendal -> inferior rectal artery
What other artery contributes to supply of the anal canal
Middle rectal arteries anastomose with the superior and inferior rectal arteries
Venous drainage above and below the pectinate line
Above - superior rectal vein which drains into the IMV
Below - inferior rectal vein which drains into the internal pudendal vein
Innervation above and below the pectinate line
Above (visceral) - inferior hypogastric plexus
Below (somatic) - inferior anal nerves which are branches of the pudendal nerve
Where is pain above the pectinate line referred to
S2-4 dermatomes
What is the anal canal sensitive to above and below the pectinate line
Above - stretch
Below - pain, touch, temperature and pressure
What does lymph drain into from above and below the pectinate line
Above - internal iliac lymph nodes
Below - superficial inguinal lymph nodes
What are haemorrhoids
Vascular cushions found within the anal canal which help with the maintenance of faecal continence
What are pathological haemorrhoids
Swollen or distended haemorrhoids
Who are pathological haemorrhoids seen in
People who suffer from:
Constipation
Prolonged straining when defecating
Raised intra-abdominal pressure (pregnancy, ascites)
Consequences of pathological haemorrhoids
Bleeding and pain on defecation
