Dr. M. Almadani
Common Ano-rectal diseases
Principles and Practice of Surgery
Pg 263-277
Anatomy
Rectum
Rectum intestinum, means straight intestine
Different definitions of the rectum:
- Surgeons define the rectum as starting at the level of the sacral promontory
- Anatomists define the rectum as starting at the level of the 3rd sacral vertebra.
- Length 12- 15 cm.
Layers
- Outer layer consists of longitudinal muscle.
- Upper third of the rectum has peritoneal cover on its front and sides,
- Middle third is peritonealized only anteriorly
- Lower third is located extraperitoneally
The superior rectal artery is the continuation of the inferior mesenteric artery, supplying the rectum and anastomosing with the middle and inferior rectal arteries (branches of the internal iliac arteries
Anal Canal
The anal canal:
- Most terminal part of the lower GI
- Completely extraperitoneal
Surgical anal canal:
- 4 cm long
- Extends from the anal verge distally, to the anorectal ring, proximally.
Anatomical anal canal:
- 2 cm long
- Extends from the anal verge distally, to the dentate line proximally.
The dentate line is the junction of the ectoderm and endoderm in the anal canal.
Blood supply of anal canal: Upper part:
- superior rectal (hemorrhoidal) artery (inferior mesenteric artery).
Lower part:
- Middle rectal artery (internal iliac artery)
- Inferior rectal artery (internal pudendal artery)
Lymphatics from the anal canal drain into the superficial inguinal group of lymph nodes
Transitional zone:
Part of anal canal just above the pectinate (dentate) line for about 1-2 cm
Anal columns (of Morgagni) are 6-10 longitudinal (vertical) mucosal folds in the upper part of the anal canal.
External anal sphincter:
3 parts:
- Subcutaneous
- Superficial
- Deep.
Skeletal muscle, is under voluntary control, and is supplied by pudendal nerves (S2-S4).
Proximally, merges with the levator ani
Internal anal sphincter:
Circular smooth muscle layer of the rectum.
Involuntary
