Digestion Lecture Notes

Structure and Function of the Small Intestine

• DJI Sequence: Duodenum, Jejunum, Ileum extends from the pyloric sphincter to the large intestine.
• Opening to Large Intestine: Cecum.
• Primary Function: Chemical digestion and nutrient absorption into the bloodstream.
• Greater Omentum: Part of the peritoneum with a lot of fat content to keep inner organs in place.

Digestion Process

• Nutrient Simplification: Necessary for absorption.
  • Nucleic acids -> Nucleotides
  • Carbohydrates -> Monosaccharides
  • Fats/Lipids -> Glycerol and Fatty Acids
  • Proteins -> Amino Acids
• Importance of Digestion: To convert food into absorbable particles.

Anatomy of the Small Intestine

• Villi: Finger-like projections increase surface area for absorption.
• Microvilli: Further increase surface area, aiding in nutrient absorption.
• Lacteals: Lymphatic vessels in villi aiding in fat absorption.
• Plicae Circulares: Circular folds to increase surface area further.

Enzymes and Their Functions

• Peptidases: Break down proteins.
• Disaccharidases: Break down sugars.
• Lipases: Break down lipids.
• Nucleases: Break down nucleic acids.

Large Intestine Structure and Function

• Ileocecal Valve: Controls movement from small to large intestine.
• Main Function: Absorbing water, storing waste.
• Bacteria and Vitamins: Bacteria in the large intestine produce vitamins like K and B12, aid in digestion.

Issues and Reflexes

• Defecation Reflex: Triggered by rectal wall stretching.
• Internal vs. External Anal Sphincters: Control voluntary and involuntary release of waste.
• Diarrhea: Rapid transit, insufficient water absorption.
• Constipation: Slow transit, excessive water absorption.

Common Digestive Problems

• Ulcers: Open sores due to bacteria; treatable with antibiotics.
• Vomiting: Reverse peristalsis.
• Gallstones: Crystallized bile causing gallbladder issues.
• Hemorrhoids: Inflamed rectal veins, often due to constipation or pregnancy.
• Lactose Intolerance: Lack of lactase enzyme causing digestive issues.
  • Treated with lactase supplements.
• Hepatitis and Cirrhosis: Liver inflammation and scarring.
• Colonoscopy: Screening for colon cancer, especially recommended after age 50.
• Heartburn: Acid reflux into esophagus, potential risk for cancer.

Additional Information

• Role of Bacteria: Essential for breakdown of fiber and production of gas (flatus).
• Environmental Concerns: Methane from cattle contributing to greenhouse gases.
• Peristaltic Movements: More pronounced in small intestine, slower in large intestine.