The Anal Canal Flashcards
where is the anal canal found within the GI tract?
The anal canal is the final segment of the gastrointestinal tract
where does the anal canal extend between?
extending between the rectum and the anus
what is the role of the anal canal?
It has an important role in defecation and maintaining faecal continence
where is the anal canal located?
The anal canal is located within the anal triangle of the perineum
what does the anal canal lie in close proximity to?
It lies in close proximity to several other important structures in the pelvis and perineum
what is anterior to the anal canal in males?
Perineal body
Urogenital diaphragm
Urethra
Bulb of the penis
what lies anterior to the anal canal in females?
Perineal body
Urogenital diaphragm
Vagina
what lies posterior to the anal canal?
Anococcygeal ligament
Coccyx and sacrum
what lies laterally to the anal canal?
Ischioanal fossae
about how long is the anal canal in length?
4cm
where does the anal canal begin?
It begins as a continuation of the rectum
which direction does the anal canal passes?
passes in an infero-posterior direction
where does the anal canal terminate?
at the anus
when is the anal canal collapsed?
during defecation
what is the anal canal collapsed by?
internal and external anal sphincters
why does the anal canal need to collapse during defecation?
to prevent the passage of faecal material
what is the anal canal surrounded by?
The anal canal is surrounded by internal and external anal sphincters
what is the function of the internal and external anal sphincters?
play a crucial role in the maintenance of faecal continence
what does the internal anal sphincter surround?
surrounds the upper 2/3 of the anal canal.
what forms the internal anal sphincter?
It is formed from a thickening of the involuntary circular smooth muscle in the bowel wall
what type of muscle is the external anal sphincter?
voluntary muscle
what does the external anal sphincter surround?
surrounds the lower 2/3 of the anal canal
what does the external anal sphincter blend in with superiorly?
It blends superiorly with the puborectalis muscle of the pelvic floor
what is the anorectal ring?
a muscular ring
where is the anorectal ring?
at the junction of the rectum and the anal canal
what is the anorectal ring formed by?
It is formed by the fusion of the internal anal sphincter, external anal sphincter and puborectalis muscle
when can the anorectal ring be palpated?
on digital rectal examination
what lines the superior aspect of the anal canal? which structure is the same lining as?
The superior aspect of the anal canal has the same epithelial lining as the rectum (columnar epithelium)
how is the mucosa organised in the anal canal? what is it known as?
organised into longitudinal folds, known as anal columns
where are the anal columns joined? what are they joined by?
joined together at their inferior ends by anal valves
what is situated above the anal valves?
anal sinuses
what are anal sinuses?
small pouches above the anal valves which are referred to as anal sinuses
what do anal sinuses contain?
contain glands that secret mucus
what do anal valves collectively form? what is it known as?
an irregular circle – known as the pectinate line (or dentate line)
what does the pectinate line divide?
This line divides the anal canal into upper and lower parts
what is different in the upper and lower parts of the anal canal?
differ in both structure and neurovascular supply
why do the upper and lower parts of the anal canal differ in both structure and neurovascular supply?
result of their different embryological origins
what is the embryonic origin of structures above the pectinate line?
derived from the embryonic hindgut
what is the embryonic origin of structures below the pectinate line?
derived from the ectoderm of the proctodeum
what is the anal canal lined by inferior to the pectinate line? what is it known as?
Inferior to the pectinate line, the anal canal is lined by non keratinised stratified squamous epithelium (known as the anal pecten)
how does anal pecten look like?
pale and smooth surface
when does anal pecten transit into skin?
anal pecten transitions at the level of the inter-sphinteric groove to true skin
what type of epithelium is true skin?
keratinised stratified squamous
