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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.
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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