1. RECTUM and ANAL CANAL

2. Rectum Begins at level of sacral vertebra 3.
Follows curvature of sacrum and coccyx.

3. Rectum Transverse rectal folds:
Three internal infoldings of the mucous and submucous layers.

4. Rectum Anorectal flexure: Ampulla: At the levator ani muscles.
Important for fecal continence.
Ampulla:
Rests on the pelvic diaphragm.
Holds the fecal mass until defecation.

5. 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.

6. Anal Canal External anal sphincter: Three rings of skeletal muscle.
Extends entire length of anal canal.
Controlled voluntarily via branches of pudendal nerve.

7. Anal Canal Anal columns:
5-10 longitudinal folds of mucosa in upper half of canal.

8. 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.

9. Anal Canal Pectinate line: Innervation above the line:
Via the ANS.
Innervation below the line:
Anococcygeal nerve (PNS).

10. Anal Canal Pectinate line: Lymphatic changes: Arterial supply:
Above the line to the cisterna chyli.
Below the line to superficial nodes.
Arterial supply:
Inferior rectal artery.
Fig. 3.43

11. Anal Canal Figures from Moore: Vessels of rectum and anal canal:
Innervation:
Figure 3.36