RECTUM

RECTUM

Definition Rectum is the lower part of the large intestine, extending from the sigmoid colon to the anus.

Location It is located in the pelvic cavity, below the level of the psoas major muscle.

Boundaries

• Superiorly: it is bounded by the sigmoid colon.
• Inferiorly: it is bounded by the anal canal.
• Anteriorly: it is bounded by the rectouterine pouch (in females) and the rectovesical pouch (in males).
• Posteriorly: it is bounded by the sacrum and the coccyx.

Layers

• Mucosa: the innermost layer, consisting of columnar epithelium.
• Submucosa: a layer of loose connective tissue below the mucosa.
• Muscularis: a layer of smooth muscle, consisting of an inner circular layer and an outer longitudinal layer.
• Serosa: the outermost layer, consisting of a layer of connective tissue.

Blood Supply

• Superior rectal artery: a branch of the inferior mesenteric artery.
• Middle rectal artery: a branch of the internal iliac artery.
• Inferior rectal artery: a branch of the internal pudendal artery.

Nerve Supply

• Splanchnic nerve: a branch of the pelvic splanchnic nerve.
• Pudendal nerve: a branch of the sacral plexus.

Muscle Action Sequence

• Fecal material from the sigmoid colon enters the rectum.
• The rectal wall stretches, triggering the urge to defecate.
• The external anal sphincter relaxes, allowing feces to pass through the anal canal.
• The internal anal sphincter relaxes, allowing feces to pass through the anus.

Lymph Drainage

• Lymph nodes in the mesorectum and the pelvis.

Anatomical Relations

• The rectum is related to the sigmoid colon, the anus, the urinary bladder, the reproductive organs, and the sacrum and coccyx. RECTUM

Morphology and Relations

• The rectum is a continuation of the sigmoid colon and extends from the 3rd sacral vertebra to the anal canal.
• It is a dilated part of the large intestine.
• The rectum is surrounded by the mesorectum, a fat-filled space that contains lymph nodes and blood vessels.
• The rectum is related to the following structures:
  • Above: Sigmoid colon, sacrum, and the pelvic cavity
  • Below: Anus and anal canal
  • Lateral: Levator ani and coccygeus muscles
  • Posterior: Sacrum and coccyx

Blood Supply

• The rectum receives its blood supply from the superior rectal artery and the middle and inferior rectal arteries.
• The superior rectal artery arises from the inferior mesenteric artery and supplies the rectum above the pectinate line.
• The middle and inferior rectal arteries arise from the internal iliac artery and supply the rectum below the pectinate line.

Nerve Supply

• The rectum is innervated by the inferior hypogastric plexus.
• The inferior hypogastric plexus receives sympathetic fibers from the thoracic splanchnic nerves and parasympathetic fibers from the pelvic splanchnic nerves.
• The rectum also receives somatic sensory fibers from the pudendal nerve.

Applied Anatomy

• The rectum is an important structure in the investigation of gastrointestinal diseases.
• The rectum is a common site for rectal examinations and biopsies.
• The rectum is also a site for the insertion of rectal tubes and instruments for the diagnosis and treatment of rectal diseases.

Text Flowchart

Inferior Mesenteric Artery → Superior Rectal Artery → Rectum (above pectinate line) Internal Iliac Artery → Middle and Inferior Rectal Arteries → Rectum (below pectinate line)