1. Anal Canal
Anal Canal

2. Definition :-
The last part of the GIT
Commences at the level where the rectum passes through the pelvic diaphragm and ends at the anal verge
Parts : -
Anorectal ring – the muscular junction between the rectum and anal canal – can be feltas a thickened ridge
Internal sphincter
Thickened continuation of the circular muscle coat of the rectum.
Pearly white
Spasm of this muscle is the cause of increased pain in many painful conditions of the anus.

3. The external sphincter
Longitudinal muscle fibres –
fan out to get attached to the skin of the anal verge.
The external sphincter
Some of its fibres are attached posteriorly to the coccyx, anteriorly inserted into the midperineal point in the male and in the female fuse with the sphincter vaginae
Pink
The intersphincteric plane
The potential space between the internal and external sphincter
Contains 8-12 apocrine glands – can cause infections
Puborectalis
This muscle maintains the angle between the rectum and the anal canal
The ano rectal ring
Junction between the rectum and the anal canal
Formed by the joining of the puborectalis muscle, the deep external sphincter, conjoined longitudinal muscle and the highest part of the internal sphincter

4. Anal valves situated at the lower end of the columns of Morgagni
Division of the anorectal ring permanent incontinence of faeces
The mucous membrane
8-12 longitudinal folds known as the columns of Morgagni
Red
Anal valves situated at the lower end of the columns of Morgagni
Just below the level of the anal valves transition of columnar epithelium to squamous epithelium – wavy margin – called the dentate line
The squamous epithelial lining of the anal canal is called the anoderm
Lower down the pale anoderm becomes pigmented

5. superior, middle and inferior haemorrhoidal veins
Arterial supply
By branches from the superior, middle and inferior haemorrhoidal arteries
Venous drainage
superior, middle and inferior haemorrhoidal veins
Lymphatic drainage
Hpper half to the para-aortic nodes
Lower half to the inguinal lymph nodes