Anus

 

  

The anus is divided into an upper part which is endodermal in origin which is covered by stratified columnar epithelium and a lower part which is ectodermal in origin and comes from the cloaca embryologically. The lower portion is covered by stratified squamous epithelium. It is surrounded by voluntary muscles  called external anal sphincter and the corrugator cutis ani which is found in the skin around the anus. A submucosa is placed below the mucosa and between the mucosa and the muscles.

The mucosa of the upper 15 mm of the canal has 6-12 longitudinal folds called anal columns. The lower ends are united by short transverse folds called anal valve. The anal valve run transversely to form the pectinate line. The region below this line is called the pectin or transitional zone. Its lower limit forms the Hilton's white line. Below this level is final skin covering the lowest 8-11mm of anal canal.

The internal anal sphincter is a continuation of the longitudinal muscle of the rectum. It extends to the level of Hiltonís white line, which is marked by the attachment of the peri-anal fascia to the wall of the anal canal.

 

 

 

 

 

 

 

 

Click here for practical, scan or tissue diagnosis   gross   embryology
histophysiology  histochemistry  histopathology  histopharmacology

 © Electronic School of Medicine
Creator: Oluwole Ogunranti

 

      

1 rectum 2 levator ani 3 anal column 4 deep part of external anal sphincter 5 superficial part of external anal sphincter 6 peri-anal fascia 7 subcutaneous part of external anal sphincter 8 internal anal sphincter 9 (Hilton's white line 10 anocutaneous junction 11 annulus hemorrhoidalis 12 pecten 13 anal sinus

 

 

 

Introduction
Histology
Embryology

Gross anatomy
Lymphatic drainage
Organ integration
Clinical anatomy

Quiz

Dissector

Physiology

Biochemistry

Pharmacology

Chemical Pathology

Anatomical Pathology

Imaging

Medicine

Surgery

Main Subject Course Links

Anatomy Anesthesia Biochemistry Chemical pathology Community Health
Dermatology ENT Gynecology Hematology Imaging
Medicine Medical microbiology Obstetrics Ophthalmology Pathology
Pediatrics Pharmacology Physiology Psychiatry    Surgery/Orthopedics
eLab eOSCE eProcedures eInvestigations eSchool/Videopage
eOrgans eLocator Anatomy Museum eDissector eFractures
All diseases eClerking eTreatment eDoctor ePatient