Lecture on the Large Intestine

Overview

• The large intestine is approximately 5 feet long.
• Opens through the anus.
• Main functions:
  • Absorb water and electrolytes.
  • Reabsorb and recycle water and digestive secretions.
  • Form and store feces until defecation.

Structure

• Cecum: Beginning of the large intestine, connects with the ileum.
  • Appendix is attached here, lymphatically active.
• Colon Segments:
  • Ascending colon
  • Transverse colon
  • Descending colon
  • Sigmoid colon
  • Rectum and anal canal leading to the anus.

Intestinal Layers

• Mucosa: Innermost layer.
• Submucosa: Outside the mucosa.
• Muscularis: Smooth muscle layer.
• Serosa: Outermost layer.

Muscle Features

• Tinea Coli: Three bands of smooth muscle.
• Haustra: Pouches that form the shape of feces.

Functions

• Not involved in digestion of carbohydrates or lipids.
• Goblet Cells: Secrete mucus to assist movement.
• Absorption of water (~90%).
• Houses intestinal flora that aid in:
  • Breakdown of substances like cellulose.
  • Production of vitamins like K, B12.
• Gas and odor primarily due to hydrogen sulfide.

Movements

• Slower and less frequent than the small intestine.
• Mass Movement:
  • Peristaltic waves, 2-3 times a day.
  • Occurs typically after meals.
• Defecation Reflex:
  • Involves deep breath, abdominal contraction.
  • Relaxation of internal and external sphincters.

Feces Composition

• 75% water, 25% solids (electrolytes, mucus, bacteria, pigments).
• Bacterial alterations lead to odor.
• Gas includes methane, nitrogen, etc.

Disorders and Conditions

• C. difficile Infection:
  • Overgrowth due to loss of E. coli, often post-antibiotic treatment.
• Diverticulitis: Inflammation of intestinal wall protrusions.
• Irritable Bowel Syndrome: Includes conditions like ulcerative colitis and Crohn's disease.
• Colorectal Cancer:
  • Linked to diet, especially bacon and grilled foods.
  • Screened through fecal occult blood test, colonoscopy.

Lifespan Changes

• Digestive efficiency declines with age.
  • Tooth enamel thins, gums recede.
  • Peristalsis slows, leading to constipation.
  • Nutrient absorption decreases.
• Increased incidence of lactose intolerance.

This concludes the lecture on the large intestine and the digestive system. Look forward to the next session.