STRUCTURE 

1.  Two sphincters guarding anus are Internal and External anal sphincters. They are present in the form of circular bands around it.

2.  During puberty pubic hair start to grow around anus and fill space around till end of puberty.

BLOOD SUPPLY

•  It receives its blood supply from Inferior Rectal Artery. It forms an anastomoses with superior rectal Artery via middle rectal Artery.
•  Blood is drained into Internal Rectal venous plexus.

NERVE SUPPLY

It receives its nerve supply through inferior anal nerve. It supplies the skin around anus and external anal sphincter. Hypogastric plexus supplies the internal anal sphincter.

FUNCTION

It allows and guards passage of feces and gases from rectum to outside the body.  For material to pass internal and external anal sphincter must relax. Internal sphincter is involuntary and relaxes in response to distension of rectum and anal canal by filling of faces and gases. External anal sphincter is voluntary and can be contracted and relaxed on will to delay or induce the expulsion of materials, respectively.

CLINICAL SIGNIFICANCE

• Anus is frequent site of warts, itching, fistulas, cancer, abscesses and hemorrhoids.
• During anal sex bruising occurs on its margins and there can be damage to sphincter muscles leading to faucal incontinence and flatulence.
• Some children are born with anal defects like narrowing and absence of anus. This can be corrected by surgery.
• For maintaining good hygiene it is recommended to wash hands and clean anal region properly after defecation etc.