Respiratory System Overview

Overview

This lecture explains the evolution, mechanisms, and anatomy of the vertebrate respiratory system, focusing on how lungs and associated structures allow efficient gas exchange using diffusion and bulk flow.

Evolution of Respiration

• About 380 million years ago, a lobe-finned fish developed lungs, enabling vertebrates to breathe air.
• Early life relied on simple diffusion of oxygen across membranes, which only works for very small or thin organisms.
• Larger organisms needed a circulatory and respiratory system to efficiently transport oxygen.

Mechanisms of Gas Exchange

• Simple diffusion moves molecules from high to low concentration but is inefficient over long distances or large bodies.
• Bulk flow is the rapid movement of large groups of molecules (e.g., inhaling air into lungs).
• The respiratory and circulatory systems cooperate to maximize oxygen delivery and carbon dioxide removal.

Human Respiratory System Anatomy

• The respiratory system is divided into the conducting zone (airways) and the respiratory zone (gas exchange sites).
• The conducting zone includes the nose, sinuses, pharynx, larynx, trachea, and bronchi.
• The respiratory zone consists of bronchioles, alveolar ducts, and alveolar sacs.

Functions and Structures

• The nose filters, warms, and moistens air to protect delicate lung tissue.
• The epiglottis covers the larynx to prevent food from entering the airway during swallowing.
• The trachea has rigid rings to prevent collapse when negative pressure is created during inhalation.
• Bronchi branch into bronchioles and end in alveoli, where gas exchange occurs.
• Alveoli are lined with thin, wet membranes, optimizing diffusion of gases.
• Lungs rely on the diaphragm and intercostal muscles to change pressure and volume for breathing.

Key Terms & Definitions

• Diffusion — passive movement of molecules from high to low concentration across membranes.
• Bulk Flow — fast movement of large quantities of molecules, such as air, driven by pressure differences.
• Alveoli — small, thin-walled air sacs in the lungs where gas exchange with blood occurs.
• Conducting Zone — part of the respiratory system that moves air but does not exchange gases.
• Respiratory Zone — regions of the lungs where actual gas exchange occurs.
• Diaphragm — major muscle below the lungs that contracts to allow inhalation.
• Trachea — the ‘windpipe’ conducting air to and from the lungs, supported by cartilage rings.
• Epiglottis — flap of tissue preventing food from entering the airway during swallowing.

Action Items / Next Steps

• Review the mechanics of diffusion vs. bulk flow.
• Memorize the anatomy and functions of the respiratory system's conducting and respiratory zones.