Lecture Notes: The Large Intestine

Anatomy and Subdivisions

• Large Intestine extends from the ileocecal sphincter to the anus.
• Subdivisions include:
  • Cecum
  • Colon (ascending, transverse, descending, sigmoid)
  • Rectum
  • Anal Canal
• Appendix is inferior to the cecum and can become inflamed, leading to appendicitis.
• Pathologies: Appendicitis can lead to gangrene or peritonitis if ruptured.

Characteristics

• Approximately five feet long and two and a half inches in diameter.
• Retroperitoneal positioning of ascending and descending parts.
• Rectum: Last 8 inches, functions as a storage chamber.
• Anal Canal: Contains two sphincters – internal (smooth muscle) and external (skeletal muscle under voluntary control).

Important Flexures and Structural Features

• Hepatic Flexure: Turn at the liver.
• Splenic Flexure: Turn near the spleen.
• Haustra: Small pouches caused by sacculation, giving the colon its segmented appearance.

Function and Histology

• Mucosa: No villi, has crypts with simple columnar epithelium and abundant goblet cells for mucus production.
• Muscularis: Contains teniae coli which contract to form haustra.
• Serosa: Visceral peritoneum; appendix contains lymphatic tissue.

Mechanical Movements

• Peristalsis and Mass Peristalsis: 3 to 12 contractions per minute.
• Haustral Churning: Movement of chyme through pouches.
• Gastroileal and Gastrocolic Reflexes: Move contents through GI tract based on stomach fullness.

Chemical Processes

• Bacterial Fermentation: Digests undigested carbohydrates, proteins, and bilirubin.
• Vitamin Production: Bacteria produce vitamins K and B.
• Water Absorption: 90% removed by the time feces reach the transverse colon.

Defecation Process

• Reflexive Movement: Aided by diaphragm and abdominal muscles.
• Voluntary Control: External sphincter can be controlled to delay defecation.
• Conditions: Diarrhea (rapid chyme movement), Constipation (slow movement).

Dietary Fiber and Health

• Insoluble Fiber: Woody parts of plants; helps prevent colon cancer.
• Soluble Fiber: Forms a gel; lowers blood cholesterol.
• Constipation Remedies: Include fiber, exercise, and increased water intake.

Diagnostic Procedures

• Colonoscopy: Uses fiber optic endoscope to examine colon lining.
• Occult Blood Test: Screens for colorectal cancer by detecting blood in feces.

Key Points

• Inflammation causes: Blockage, foreign bodies, carcinoma, stenosis, kinking.
• Symptoms of appendicitis: High fever, elevated white blood cell count, localized pain, nausea.
• Most chemical digestion in large intestine is due to bacterial activity rather than enzyme secretion.