Anorectal Diseases

16 Anorectal Diseases



Anorectal Anatomy



image

General Anorectal Anatomy



Rectum



• Wider diameter than most of colon, except for cecum

• 12-16 cm in length, starting at about the sacral promontory, extending to dentate line of anal canal

• Anterior aspect of upper 4-6 cm is intraperitoneal, with serosal surface.

• Lower (majority of) rectum lies within extraperitoneal pelvis, with no serosa.

• Taeniae coli spread out at rectosigmoid junction to form a continuous, external longitudinal muscle layer.

• Three flexures of rectum usually correspond with 3 transverse rectal folds (superior, middle, and inferior rectal valves).

• Valves overlie thickenings of circular muscle.

• Ampulla: terminal portion rectum below inferior valve, supported by levator ani and anococcygeal ligament

• Women: thin rectovaginal septum separates anterior inferior rectum from vagina

• Men: prostate and seminal vesicles lie anterior to inferior rectum

• Mucosa: columnar epithelium, down to dentate line


Anal Canal



• 3-5 cm in length, from level of levator ani muscles to anal verge

• Canal includes dentate line, anal glands, internal and external sphincter muscles, and hemorrhoidal vessels.

• External anal sphincter muscles: striated muscle, with somatic innervation under voluntary control

• Internal anal sphincter muscle: continuation of inner, circular smooth muscle of hindgut, with autonomic (involuntary) innervation

• Stratified squamous epithelium lines anal canal, beginning at dentate line.


Microscopic Anatomy



• Mucosa
image Epithelium: enterocytes (absorptive), goblet cells

image Lamina propria

image Muscularis mucosa

• Submucosa
image Strongest layer (connective tissue)

image Meissner’s plexus (neuronal network)

• Muscularis
image Auerbach’s plexus: myenteric neurons

image Inner circular muscle

image Outer longitudinal layer: 3 bands of colic taeniae coli merge into a continuous layer at rectosigmoid junction, down through sphincter level

• Serosa
image Peritoneum only on anterior superior part of rectum

image Rest is extraperitoneal, in contact with endopelvic fascia.

image

Rectal/Pelvic Nerves

Related posts:

  1. Uterus and Adnexal Diseases
  2. Pancreatic Diseases
  3. Pelvic Fractures
  4. Liver Diseases

Stay updated, free articles. Join our Telegram channel
Tags:
Aug 12, 2016 | Posted by in ANATOMY | Comments Off on Anorectal Diseases

Full access? Get Clinical Tree
Get Clinical Tree app for offline access