뒤로The Respiratory System: Gas Exchange, Transport, and Regulation
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The Respiratory System
Overview
The respiratory system is responsible for the exchange of gases between the atmosphere, blood, and tissues, supporting cellular respiration and maintaining homeostasis. This study guide covers the mechanisms of gas exchange, transport, and regulation within the human body.
Objectives
Explain the partial pressures of oxygen and carbon dioxide in systemic and pulmonary circulation, as well as at the alveolar and tissue levels.
Discuss ventilation-perfusion coupling and its role in efficient gas exchange.
Describe the effects of pH, temperature, and pCO2 on oxygen loading and unloading.
Explain carbon dioxide transport in the blood.
Discuss the neural controls of respiration.
Define hyperventilation and hypoventilation.
Understand the types of hypoxia and their causes.
Give examples of homeostatic interrelationships between the respiratory system and other body systems.
Gas Exchanges Between Blood, Lungs, and Tissues
Types of Respiration
External respiration: Diffusion of gases (O2 and CO2) in the lungs between alveoli and blood.
Internal respiration: Diffusion of gases at the body tissues between systemic capillaries and tissue cells.
Both processes depend on the physical properties of gases and the composition of alveolar gas.
Basic Properties of Gases
Dalton's Law of Partial Pressures
Dalton's Law states that the total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted by each individual gas.
Partial pressure: The pressure exerted by each gas in a mixture, directly proportional to its percentage in the mixture.
Equation:
For example, in atmospheric air:
Oxygen: mm Hg
Nitrogen: mm Hg
Total: mm Hg
Henry's Law
Henry's Law describes how gases dissolve in liquids in proportion to their partial pressures. At equilibrium, the partial pressure of a gas in the liquid equals that in the gas phase.
Solubility: CO2 is about 20 times more soluble in water than O2; N2 has very low solubility.
Temperature: As temperature increases, gas solubility decreases.
Composition of Alveolar Gas
Differences from Atmospheric Air
Alveoli contain more CO2 and water vapor than atmospheric air.
Gas exchanges in the lungs, humidification of air, and mixing of alveolar gas with each breath alter the composition.
Gas | Atmosphere % | Atmosphere Partial Pressure (mm Hg) | Alveoli % | Alveoli Partial Pressure (mm Hg) |
|---|---|---|---|---|
N2 | 78.6 | 597 | 74.9 | 569 |
O2 | 20.9 | 159 | 13.7 | 104 |
CO2 | 0.04 | 0.3 | 5.2 | 40 |
H2O | 0.46 | 3.7 | 6.2 | 47 |
Total | 100.0 | 760 | 100.0 | 760 |
External Respiration
Mechanisms and Influencing Factors
External respiration is the exchange of O2 and CO2 across the respiratory membrane in the lungs. It is influenced by:
Thickness and surface area of the respiratory membrane: Thinner membranes and larger surface areas facilitate efficient gas exchange.
Partial pressure gradients and gas solubilities: Gases move from areas of higher to lower partial pressure; solubility affects the rate of diffusion.
Ventilation-perfusion coupling: The matching of air flow (ventilation) and blood flow (perfusion) to optimize gas exchange.
Additional info:
Partial pressure gradients for O2 and CO2 drive their movement between alveoli and blood.
O2 diffuses from alveoli (high PO2) to blood (low PO2); CO2 diffuses from blood (high PCO2) to alveoli (low PCO2).
Diseases that thicken the respiratory membrane or reduce its surface area (e.g., emphysema, pulmonary edema) impair gas exchange.
