Dr Dur e Shahwar Rehman
Assistant Professor
Dept. Of Anatomy
SMC
JSMU
22/05/2014
DEPARTMENT OF ANATOMY
LECTURE OBJECTIVES AND OUTLINE
LECTURE
HISTOLOGY OF ANAL CANAL
OBJECTIVES:
At the end of the lecture the students should be able to:
– Know the basic anatomy of large intestine
– Review the important histological features of large intestine
– Know the basic histological features which differentiate large intestine from small
Intestine
_Identify the histological zones
– Recognize the characteristics of anorectal regions
OUTLINE:
Anal Canal
• The anal canal is the 2.5-4 cm long terminal part of the digestive tract.
• The mucosa has a characteristic surface relief of 5-10 longitudinal folds, the anal
columns.
• Each column contains a terminal branch of the superior rectal artery and vein.
• Small mucosal folds between the anal columns (anal valves) form the pectinate line.
• This line defines sections of the anal canal with different arterial and nerve supplies,
different venous and lymphatic drainages and different embryological origins.
• Crypts disappear below the pectinate line
• the epithelium changes from the tall, columnar type seen in other parts of the large
intestine to a stratified squamous epithelium.
• The muscularis externa gradually becomes thicker and forms the involuntary internal
anal sphincter.
The anal canal is divided into three parts.
· The zona columnaris is the upper half of the canal.
· The lower half of the anal canal, below the pectinate line, is divided into two zones separated by Hilton's white line.
· The two parts are
a) zona hemorrhagica
b) zona cutanea
Histologically the anal canal has short zones covered with different types of epithelium from proximal to distal end.
· Rectal zone with colonic type of mucosa
· Transitional zone varying with colonic mucosa and squamous epithelium
· Squamous epithelium zone with non-keratinizing squamous epithelium
· Perianal skin with keratinizing squamous cell epithelium