Flashcards in Perineum - anus (dave's notes) Deck (19):
Describe the anus
The anus is the last four centimetres of the GI tract
What did the anus develop from?
The antorectal canal and proctodeum
Describe the muscle layers of the anus
There are two layers of muscle fibres; internal (visceral) and external (skeletal). Both of these are circular.
Where is the junction between the rectum and the anal canal?
At the pelvic floor. Puborectalis angles the gut forward.
If the anus is a tube within a funnel, what structures make up these components?
Levator ani down to the external sphincter is the funnel, and the inner sphincter (a continuation of rectal muscle) is the inner tube.
What does the rectal end of the external sphincter blend with? What is this line of fusion called?
Puborectalis, the anorectal ring
Describe the shape and attachments of the middle part of the external anal sphpincter
The middle part is elliptical, attatched to the coccyc and perineal body
Where is the lower part of the external anal sphincter found?
Subcutaneous, cuffing around the internal anal sphincter
Regarding the external anal sphincter, what occurs at the anorectal junction?
The outer longitudinal layer fuses with puborectalis
Describe the internal anal sphincter
This is a thickened downward continuation of the inner circular muscle of the rectum
Describe the mucous membrane of the upper third of the anus
The upper third has up to 12 longitudinal ridges - anal columns which are joined together
What is found at the base of the anal columns? How else is this area known?
The anal valves or sinuses. This is the pectinate or dentate line. Here are mucous secreting anal glands.
What is found below the dentate line?
A band of pecten to the interphincteric groove - (Hilton's white line) - and then cutaneous skin
What does the upper part of the mucous membrane develop from? What does the lower part develop from?
Upper - cloaca, lower - proctodeum
What is the blood supply of the anus?
The superior rectal artery. The muscle wall is from supplied by the middle rectal and median sacral arteries. The lower end and mucous membrane is supplied by the interior rectal artery.
Describe the venous drainage of the anus
Venous drainage corresponds with blood supply, and is continuous with the rectal venous plexus. The upper end drains via the portal system, and the lower end drains via the internal iliac vein.
Describe the lymphatic drainage of the anus
Lymphatic drainage shows a watershed corresponding with the vascular pattern.
What is the nerve supply of the external anal sphincter?
The interior rectal branches of the pudendal nerve supply the external sphincter.