Anal Canal-An Over View
The anal canal is the terminal part of the broad intestine, that is below the level of the pelvic diaphragm, between the rectum and the anus. It is situated between the right and left ischioanal fossas in the anal triangle of the perineum. It acts as the bowel’s final functional part, controlling excrement release through two muscular sphincter complexes. The anus is the terminal part of the anal canal’s aperture. The transformation of its internal surface from a mucous membrane layer (endodermal) to one of skin-like tissue distinguishes the anal canal from the rectum (ectodermal). Canal anesthetic:
The colorectal zone, which is lined by uninterrupted glandular mucosa, is the proximal zone of the anal canal. The squamous zone, which is lined by continuous squamous mucosa, is the distal zone. The transition zone is located in the middle and includes a variety of epithelia. The anal valves, anal sinuses, and bases of anal columns are all part of the dentate line, which runs along the anal canal. The extent of the specialized mucosa, i.e., the transitional zone and squamous zone down to the perianal skin, determines the histologic anal canal. When it comes to orienting biopsies from this region, the dentate line is an important anatomical landmark.
From the anorectal junction to the anus, the anal canal in humans is around 2.5 to 4 cm long. It’s pointing backward and downwards. The lumen is close in the shape of an anteroposterior slit by inner involuntary and outer voluntary sphincters. The canal is separate from the rectum by a transition from endodermal to skin-like ectodermal tissue along the internal surface.
Anal canal segments:
The upper and lower parts of the anal canal are historically distinguishing the pectinate line:
Area Columnar (upper zone):
Simple columnar epithelium lines the mucosa.
Longitudinal folds or elevations of tunica mucosa are joining inferiorly by anal valves, which are folds of the mucous membrane.
The superior rectal artery is the source of this supply (a branch of the inferior mesenteric artery)
Zone at the bottom:
A white line known as Hilton’s line divides the area into two smaller zones:
Hemorrhagic zone, with stratified squamous non-keratinized epithelium lining it.
Zone Hut – a stratified squamous keratinized epithelium that blends in with the perianal skin around it.
The inferior rectal artery is the source of this supply (a branch of the internal pudendal artery)
Zone Separation Line:
The anal verge is a transitional region between the anal canal epithelium and the perianal skin at the distal end of the anal canal. There is no confusion with the anal canal’s pectinate line, which separates the upper and lower areas. The anal gland secretes lymph and accumulated feces from the colon lining. In certain species, gland expungement can perform on a regular basis every 24–36 months to avoid infection and the development of fistulas.
Length of the Anal Canal:
The distance travels the parallel borders of the anal canal until they form the diverging walls of the distal rectum is referring to as anal canal length. The average length of the anal canal in women is 16 mm (range: 6 to 26 mm) and 22 mm (range: 10 to 38 mm) at rest. The anal canal lengthens to a mean of 19 mm (range, 9 to 26 mm) in women and 28 mm (range, 12 to 45 mm) in men during lifting (squeezing). The canal shortens slightly during straining, and in young women, it measures 14 mm (range, 6 to 20 mm) and in young men, it measures 17 mm (range, 9 to 27 mm).
The Anal Canal’s upper reaches:
At the point where it passes through a muscular pelvic diaphragm, the anal canal interacts with the rectum. There are 5 to 10 rectal columns in the upper region, each with a small artery and vein. Hemorrhoids are enlargements of the terminal portions of the blood vessels that supply the rectal and anal areas; they are vulnerable to enlargement. The upper mucous membrane is similar to the rest of the large intestine in that it contains mucus-producing and absorptive cells.
The Anal Canal’s lower reaches:
Tiny concentric circular folds of the mucous membrane known as anal valves connect the lower portions of the anal columns. Tiny anal sinuses open to lymph ducts and glands between the valves; these may become abscessed and infected, particularly in people who have chronic diarrhea, constipation, or diabetes. The anal canal’s internal wall is lining wet, soft skin with no hair or glands at first, then a rough layer of skin with hair and glands. Circular and longitudinal muscle layers exist in both the upper and lower parts of the anal canal, allowing the canal to expand and contract. The anal opening is keratinized skin with many folds when contract. The folds allow the skin to stretch without tearing when they are open. Perspiration glands is finding in the skin around the anal opening but not directly adjacent to it.
Constriction of the muscles:
Two muscular constrictions that control fecal passage make up the lower anal canal and the anal opening. The internal sphincter is setting on the canal’s inner surface. The external sphincter is a layer of voluntary muscle that surrounds the anal canal and anal opening on the outside. Except during the early years of life, when it is not completely forming, it can expand and contract at will. Sphincter reactions and pain sensations are causing by nerves in the anal canal. The lower canal is extremely sensitive to heat, cold, and cutting.