Overview
This lecture covers the human digestive system, including its main organs, the nutrients derived from food, and the four key processes: ingestion, absorption, assimilation, and excretion.
Importance and Function of Digestion
- Digestion breaks down food into small, soluble molecules for energy, growth, repair, and general health.
- The body requires carbohydrates (energy), proteins (growth and repair), fats (energy storage and insulation), vitamins, and minerals (health maintenance).
- Physical size and chemical bonds of food require both mechanical and chemical digestion.
Organs of the Digestive System and Their Roles
- The digestive system is a 9-meter-long tract including the mouth, esophagus, stomach, small intestine, large intestine (colon), rectum, and anus.
- Accessory organs include the liver (produces bile, cleanses blood), pancreas (releases digestive enzymes), and gallbladder (stores and releases bile).
- The mouth starts both mechanical (chewing) and chemical (saliva) digestion.
- The esophagus uses peristalsis (wave-like muscle movements) to move food to the stomach.
- The stomach churns food and secretes acid and enzymes for further breakdown.
- The small intestine completes digestion and absorbs nutrients with the help of villi (tiny finger-like projections).
- The large intestine absorbs water and forms feces; the rectum stores stool until it is expelled via the anus.
Stages of Digestion
- Ingestion: Intake and initial breakdown of food in the mouth using teeth and saliva.
- Absorption: Small intestine absorbs nutrients into the bloodstream through the villi for distribution to the body.
- Assimilation: Absorbed nutrients transported to cells and used for growth, repair, and energy.
- Ejection: Removal and expulsion of indigestible waste via the rectum and anus.
- Excretion: Elimination of metabolic waste from cells, such as carbon dioxide.
Key Terms & Definitions
- Peristalsis — Automatic muscle contractions that move food through the digestive tract.
- Villi — Finger-like projections in the small intestine increasing surface area for nutrient absorption.
- Bile — Digestive fluid produced by the liver, stored in the gallbladder, and released into the small intestine to aid fat digestion.
- Enzymes — Proteins that speed up chemical breakdown of food.
- Assimilation — Process of delivering absorbed nutrients to body cells.
Action Items / Next Steps
- Arrange the steps of digestion in the correct order as a practice activity.
- Label the parts of the digestive system and describe their functions.
- Identify the correct process (ingestion, absorption, assimilation, ejection, excretion) given different digestive scenarios.
- Read/review the module provided in the lesson for more detailed study.