Human Digestive System Functions and Anatomy

Human Digestive System

Two Types of Digestion

• Mechanical digestion: The physical breakdown of food.
  • Examples: Chewing in the mouth, churning in the stomach, and segmentation in the small intestine.
• Chemical digestion: Breaking down molecules with enzymes and acids.
  • Examples: Salivary amylase in the mouth, pepsin in the stomach, and pancreatic enzymes in the small intestine.

The GI Tract Path

Mouth → Pharynx → Esophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus.

Accessory Organs and Their Roles

• Salivary glands: Produce saliva.
• Liver: Produces bile.
• Gallbladder: Stores and concentrates bile.
• Pancreas: Produces digestive enzymes and bicarbonate.

Digestive Juices and Functions

• Saliva: Moistens food and initiates carbohydrate digestion.
• Gastric juice: Contains acid and enzymes for protein digestion.
• Bile: Emulsifies fats.
• Pancreatic juice: Contains enzymes for carbohydrates, proteins, and fats, plus bicarbonate to neutralize acid.
• Intestinal juice: Helps complete digestion in the small intestine.

Stomach Protection Mechanisms

The stomach is protected by a mucus barrier and bicarbonate, which shield its lining from acid and enzymes. The cells of the stomach lining are also specialized to resist damage.

Gastrointestinal Tract Movements

• Swallowing: Moves food from the mouth to the esophagus.
• Peristalsis: Wave-like contractions that move food forward.
• Segmentation: Mixes food in the small intestine.
• Churning: Mixes food in the stomach.

The Role of the Microbiome

The microbiome is the community of helpful bacteria in the digestive tract. It assists with digestion, vitamin production, and protection against harmful microbes.

Small vs. Large Intestines

• Small intestine: The main site of digestion and nutrient absorption.
• Large intestine: Absorbs water and electrolytes, forms feces, and stores waste.

Adaptations for Nutrient Absorption

• Villi: Increase surface area.
• Microvilli: Increase surface area even further.
• Thin walls: Make diffusion easier.
• Rich blood supply: Carries absorbed nutrients away quickly.
• Lacteals: Absorb fats.

Key Digestive Terminology

• Bolus: Chewed food mixed with saliva before swallowing.
• Chyme: Semi-liquid mixture of partially digested food in the stomach.
• Feces: Waste material eliminated through the anus.

Intestinal Food Pathways

Small Intestine:

1. Duodenum
2. Jejunum
3. Ileum

Large Intestine:

1. Cecum
2. Ascending colon
3. Transverse colon
4. Descending colon
5. Sigmoid colon
6. Rectum

Fast Memorization Facts

Reproductive System Basics

• Male path: Testes → Epididymis → Vas deferens → Urethra.
• Female path: Ovary → Uterine tube → Uterus → Cervix → Vagina.
• Fertilization site: Uterine tube.
• Ovulation release: Secondary oocyte.

Digestive System Summary

• Mechanical: Physical breakdown.
• Chemical: Enzymes and acids.
• Small intestine: Digestion and absorption.
• Large intestine: Water absorption and feces.
• Bile: Fat emulsifier.