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RECTUM and ANAL
CANAL
Rectum
Begins at level of sacral vertebra 3.
 Follows curvature of sacrum and coccyx.

Rectum

Transverse rectal folds:
Three internal infoldings of the mucous and
submucous layers.
Rectum

Anorectal flexure:
At the levator ani muscles.
Important for fecal continence.

Ampulla:
Rests on the pelvic diaphragm.
Holds the fecal mass until defecation.
Anal Canal

Internal anal sphincter:
Thick ring of circular smooth muscle.
Surrounds upper part of anal canal.
Controlled reflexively and involuntarily
by ANS:
Parasympathetic system
promotes relaxation.
Sympathetic system
promotes contraction.
Anal Canal

External anal sphincter:
Three rings of skeletal muscle.
Extends entire length of anal
canal.
Controlled voluntarily via
branches of pudendal nerve.
Anal Canal

Anal columns:
5-10 longitudinal folds of mucosa in upper
half of canal.
Anal Canal

Pectinate line:
Marks junction between endoderm
portion of anal canal and ectoderm
portion of anal canal (proctodeum).
Marks division between visceral and
somatic arterial, venous, lymphatic, and
nerve supply.
Anal Canal

Pectinate line:
Innervation above the line:
Via the ANS.
Innervation below the line:
Anococcygeal nerve (PNS).
Anal Canal

Pectinate line:
Lymphatic changes:
Above the line to the cisterna
chyli.
Below the line to superficial nodes.
Arterial supply:
Inferior rectal artery.
Fig. 3.43
Anal Canal

Figures from Moore:
Vessels of rectum and anal canal:
Figure 3.34.
Innervation:
Figure 3.36