Anal Canal: Lining

Question 1

Upper part (15m)

Answer 1

1. Endodermal in origin (from cloaca) lined by mucous membrane shows number of longitudinal ridges (anal columns of Morgagni) which are connected together at their lower ends by anal valves of Ball
2. Line at anal valves level (pectinate line) is site of fetus anal membrane
3. Anal sinuses
4. Endodermal supplied by autonomic nerves and is not sensitive to pain

Question 2

Anal sinuses

Answer 2

Small recesses above anal valves in which open anal glands ducts present in submucosa

Question 3

Lower part (25 mm)

Answer 3

2 parts:
Transitional zone of pecten(15 mm):
1. Extends from pectineal line above to white line of Hilton below
2. Transitional in structure between mucous membrane above and true skin below
3. Lined by non keratinized stratified squamous epithelium with no sweat glands (false skin)
Cutaneous part (10mm): Ectodermal in origin (from proctodeum) lined by true skin
Ectodermal is supplied by somatic nerves and is sensitive to pain