Overview
This lecture covers the human gas exchange system, focusing on the structure of the lungs, the mechanics of ventilation, and alveolar adaptations for efficient gas exchange.
Key Terms and Concepts
- Breathing is the movement of air in and out of the lungs.
- Respiration is the chemical reaction in cells that releases energy as ATP.
- Ventilation is a scientific term for breathing.
- Gas exchange is the diffusion of oxygen from alveoli into blood and carbon dioxide from blood to alveoli.
Structure of the Human Gas Exchange System
- The human gas exchange system includes the lungs, trachea, bronchi, bronchioles, and alveoli.
- The trachea (windpipe) has C-shaped cartilage rings to keep it open.
- The trachea branches into two bronchi, which further branch into bronchioles ending in alveoli.
- Alveoli are tiny air sacs surrounded by capillaries for gas exchange.
Mechanics of Ventilation (Breathing)
- The diaphragm (a muscle under the lungs) and intercostal muscles (between the ribs) control ventilation.
- The external and internal intercostal muscles work as antagonistic pairs (one contracts as the other relaxes).
- Inspiration (inhaling): external intercostal muscles and diaphragm contract; ribcage moves up and out; thoracic volume increases, pressure drops, and air enters lungs.
- Expiration (exhaling): internal intercostal muscles contract, external relax; diaphragm relaxes and domes; ribcage moves down and in; thoracic volume decreases, pressure rises, and air exits lungs.
Gas Exchange in the Alveoli
- Alveoli provide a large surface area (about 300 million per lung).
- Walls of alveoli and capillaries are one cell thick, providing a short diffusion distance.
- A network of capillaries maintains a constant concentration gradient for oxygen and carbon dioxide.
- Oxygen diffuses from alveolar air into blood; carbon dioxide diffuses from blood into alveoli.
Key Terms & Definitions
- Breathing — movement of air into and out of the lungs.
- Respiration — cellular process releasing energy as ATP.
- Ventilation — scientific term for breathing.
- Gas exchange — diffusion of gases (O₂ and CO₂) between alveoli and capillaries.
- Alveoli — tiny air sacs in lungs where gas exchange occurs.
- Intercostal muscles — muscles between ribs aiding in breathing.
- Diaphragm — muscle beneath the lungs involved in breathing.
Action Items / Next Steps
- Review diagrams of the respiratory system and gas exchange.
- Practice describing the roles of muscles during ventilation.
- Learn adaptations of alveoli for gas exchange.
- Prepare to explain differences between breathing, ventilation, and respiration.