3.1 Digestive System

Organs of the Digestive System and their Functions

1. Mouth: Ingestion, mechanical digestion (chewing), chemical digestion (salivary amylase).
2. Pharynx: Passageway for food.
3. Esophagus: Transports food to stomach via peristalsis.
4. Stomach: Stores food, mixes with gastric juices (HCl, pepsin), churns into chyme; protein digestion begins.
5. Small Intestine: Primary site for digestion completion and nutrient absorption.
6. Large Intestine: Absorbs water and electrolytes; forms feces.
7. Rectum: Stores feces.
8. Anus: Expels feces.

Process of Digestion

• Breakdown of complex food substances into simpler, absorbable forms.

Carbohydrates

• Mouth: Salivary amylase begins starch digestion.
• Small Intestine: Pancreatic amylase and intestinal enzymes complete breakdown to monosaccharides (e.g., glucose).

Process of Digestion (Continued)

Proteins

• Stomach: Pepsin (activated by HCl) begins protein digestion to polypeptides.
• Small Intestine: Pancreatic proteases (e.g., trypsin) and intestinal peptidases break down to amino acids.

Fats

• Small Intestine: Bile (from liver/gallbladder) emulsifies fats. Pancreatic lipase breaks down emulsified fats into fatty acids and glycerol.