Overview
This lecture covers the different systems of gas exchange in various organisms, focusing on human respiratory anatomy, physiological processes, and protective mechanisms.
Functions and Evolution of Gas Exchange
- The respiratory system delivers oxygen to tissues and removes carbon dioxide waste.
- Simpler organisms use diffusion for gas exchange, while larger animals evolved specialized tissues like gills and lungs.
- Animal size and body structure determine the complexity of the respiratory system.
Direct Diffusion
- Unicellular and small, flat multicellular organisms rely on direct diffusion across membranes for gas exchange.
- Bodies must be thin and moist to allow efficient diffusion of gases.
Skin and Gills
- Earthworms and amphibians use moist skin with capillaries for gas exchange.
- Aquatic animals like fish use gills with large surface areas for oxygen extraction from water.
- Oxygen diffuses from water (high concentration) into blood (low concentration) through gill capillaries.
Tracheal Systems in Insects
- Insects have a tracheal system—networks of chitin-lined tubes (tracheae) connected to spiracles for direct air delivery.
- The insect circulatory system is not involved in oxygen transport.
Mammalian Respiratory System Overview
- Air enters through the nasal cavity, passing through pharynx, larynx, trachea, bronchi, bronchioles, and finally into alveoli.
- The trachea is supported by incomplete cartilage rings and lined with mucus and cilia for protection.
- The right lung has three lobes; the left lung has two lobes.
Bronchi, Bronchioles, and Alveoli
- Bronchi branch into smaller bronchioles, which lead to alveolar ducts and clusters of alveoli.
- Alveoli are thin-walled, grape-like sacs where gas exchange with capillaries occurs.
- Large alveolar surface area (about 75 m²) ensures efficient gas exchange.
Protective Mechanisms of the Respiratory System
- Nasal hairs and mucus trap particulates, bacteria, and viruses before air enters the lungs.
- Mucus and ciliated cells in bronchi and bronchioles move trapped particles up to the throat for elimination.
- Smoking impairs cilia and mucus clearance, increasing respiratory disease risk.
Key Terms & Definitions
- Diffusion — passive movement of molecules from high to low concentration.
- Gills — folded tissues in aquatic animals for extracting oxygen from water.
- Tracheal system — network of air tubes in insects delivering oxygen directly to tissues.
- Spiracles — external openings on insect bodies for air entry.
- Alveoli — tiny lung sacs where gas exchange occurs with blood.
- Cilia — hair-like projections that move mucus and debris out of airways.
Action Items / Next Steps
- Review the structure and pathway of air in the human respiratory system.
- Watch the recommended video on the respiratory system for visual reinforcement.
- Understand how different organisms adapt their respiratory systems to their environments.