Lecture Notes: Human Digestive System

Introduction

• Mention of platypus as a unique mammal
  • Platypuses lay eggs and males have venomous spurs
  • Platypuses lack a traditional stomach as defined by gastric glands and gastric juice production
• Transition to focus on the human digestive system

Overview of Human Digestive System

• Four Major Tasks:
  1. Ingestion: Taking in food
  2. Digestion: Breaking down biomolecule polymers (carbs, lipids, proteins, nucleic acids)
  3. Absorption: Nutrient absorption into cells
  4. Elimination: Removal of waste

Detailed Digestive Process

Ingestion

• Food enters through the mouth
• Saliva: Contains enzymes (e.g., salivary amylase) and buffers
  • Begins chemical digestion
  • Mechanical digestion via teeth
  • Saliva lubricates food, forming a bolus
• Epiglottis: Prevents food from entering the trachea during swallowing

Esophagus

• Peristalsis: Wave-like muscle movements pushing food to the stomach

Stomach

• Storage for food and liquid (~2 liters)
• Chemical Digestion: Hydrochloric acid, pepsin enzyme
• Mechanical Digestion: Stomach churning
• Chyme: Mixture after digestion in the stomach
• Sphincters: Control passage to/from stomach
• Protection: Mucus layer and rapid cell division prevent self-digestion

Small Intestine

• Three parts: Duodenum, Jejunum, Ileum (mnemonic: DJ Ivan)
• Major site for chemical digestion and absorption
• Enzymes and Juices: From gallbladder, liver, pancreas
• Nutrient Absorption: Glucose, amino acids, vitamins, etc.
• Villi and Microvilli: Increase surface area for absorption and are vascular

Large Intestine (Colon)

• Function: Reabsorbs water, houses beneficial bacteria
• Feces: Composed of undigested contents and bacteria
• Rectum: Stores feces before elimination

Accessory Organs

• Liver: Produces bile, metabolizes carbohydrates and proteins
• Gallbladder: Stores bile
• Pancreas: Produces digestive enzymes, neutralizes chyme

Related Hormones and Disorders

• Hormones play roles in regulating digestion
• Common digestive disorders:
  • Celiac Disease: Involves small intestine
  • Diverticulitis: Involves large intestine
  • Heartburn (GERD): Involves stomach and esophagus

Conclusion

• Encouragement to learn more and understand the human digestive system
• Ends with reminder to stay curious