Lecture Notes on Digestion

Introduction to the Platypus and Digestion

• Platypus is a unique mammal that lays eggs.
• Male platypuses have venomous spurs.
• Fascinating fact: If stomach is defined as an organ with gastric glands, platypus does not have a stomach.
• This raises questions about the digestive system of the platypus vs. other mammals.

Understanding Digestion in Mammals

• Common misconception: Digestion is often equated solely with the stomach.
• Digestion involves more than just the stomach, for both humans and platypuses.

Overview of Human Digestive System Tasks

1. Ingestion: Taking in food.
2. Digestion: Breaking down biomolecule polymers into building blocks (carbohydrates, lipids, proteins, nucleic acids).
3. Absorption: Nutrients are absorbed into the body.
4. Elimination: Removal of undigested waste.

The Process of Digestion in Humans

Ingestion

• Begins in the mouth; saliva is released.
• Salivary amylase in saliva breaks down carbohydrates.
• Mechanical digestion occurs via teeth grinding food.

Mouth Functions

• Saliva helps prevent tooth decay by counteracting acidity.
• Lubrication for the food, forming a bolus.

Esophagus

• Bolus is swallowed and travels down the esophagus.
• Epiglottis prevents food from entering the trachea.
• Peristalsis: Wave-like movements that push food down.

Stomach

• Can store about 2 liters of food/liquid.
• Contains gastric juices (hydrochloric acid, pepsin) for chemical digestion.
• Mechanical digestion occurs via churning to create chyme.
• Protective mucus layer prevents the stomach from digesting itself.

Small Intestine

• Comprises three parts: Duodenum, Jejunum, Ileum (mnemonic: DJ Ivan).
• Primary site for significant chemical digestion and absorption.
• Enzymes from gallbladder, liver, and pancreas aid digestion.
• Nutrient absorption occurs through villi and microvilli, increasing surface area.

Large Intestine (Colon)

• Hosts beneficial bacteria that produce vitamins.
• Major role: reabsorb water to prevent dehydration.
• Feces consist of undigested materials and bacteria.
• Rectum stores feces until elimination occurs.

Accessory Organs in Digestion

• Liver: Largest internal organ; involved in metabolism and bile production.
• Gallbladder: Stores bile for lipid breakdown.
• Pancreas: Produces digestive juices and neutralizes stomach acid.

Disorders of the Digestive System

• Celiac Disease: Issues with the small intestine.
• Diverticulitis: Issues with the large intestine.
• Heartburn (GERD): Stomach contents entering the esophagus.

Conclusion

• Understanding the human digestive system helps in managing disorders.
• Encouragement to stay curious about biology and digestion.