Overview
This lecture covers the key structures, functions, and adaptations of the mammalian gas exchange system, focusing on the human respiratory tract and efficient gas exchange in the lungs.
Key Structures of the Gas Exchange System
- Air enters via the nasal cavity or mouth, passes the trachea, bronchi, bronchioles, and ends at the alveoli.
- The trachea (windpipe) is a large tube with ciliated epithelium and c-shaped cartilage rings for support.
- Bronchi are smaller airway tubes with ciliated epithelium and irregular cartilage plates, branching into bronchioles.
- Bronchioles have simple ciliated epithelium, smooth muscle, and lack cartilage in smaller branches.
- Alveoli are end-point air sacs with one-cell-thick walls for efficient gas exchange.
Functions and Adaptations of Respiratory Structures
- Ciliated epithelium sweeps mucus and trapped particles up and out of the lungs.
- Goblet cells produce sticky mucus to trap dust and pathogens.
- Cartilage in trachea and bronchi prevents airway collapse and keeps airways open.
- Smooth muscle can constrict airways in response to irritants, regulating airflow.
- Elastic fibers enable stretch and recoil of airways during breathing.
Gas Exchange Process and Adaptations
- Oxygen diffuses from alveoli (high concentration) into blood (low concentration); carbon dioxide diffuses in the opposite direction.
- Millions of alveoli provide a large surface area for maximum gas exchange.
- Alveoli and capillary walls are one squamous epithelial cell thick, minimizing diffusion distance.
- Moist lining of alveoli allows gases to dissolve before diffusing.
- Ventilation and continuous blood flow maintain concentration gradients for efficient diffusion.
Distribution of Tissues and Cells
- Cartilage: Trachea and main bronchi for structural support.
- Ciliated epithelium: Nasal cavity, trachea, and bronchi to move mucus.
- Goblet cells: Throughout respiratory epithelium to secrete mucus.
- Smooth muscle: Bronchioles to regulate airway diameter and airflow.
- Capillaries: Dense network around alveoli to sustain rapid gas exchange.
Key Terms & Definitions
- Trachea — Windpipe; main airway supported by cartilage.
- Bronchi (Bronchus) — Major airway branches leading to each lung.
- Bronchioles — Smaller airway branches without cartilage.
- Alveoli — Tiny air sacs where gas exchange occurs.
- Ciliated epithelium — Cells with hair-like structures moving mucus.
- Goblet cells — Mucus-secreting cells in the respiratory tract.
- Squamous epithelial cells — Flat cells forming alveolar and capillary walls.
- Cartilage — Flexible tissue preventing airway collapse.
- Smooth muscle — Muscle in airway walls regulating diameter.
- Elastic fibers — Proteins enabling airway stretch and recoil.
Action Items / Next Steps
- Review the summary sheet on distribution of tissues and cells in the gas exchange system.
- Study photo and electron micrographs to identify respiratory structures.
- Revise definitions and functions of all key terms.