Biology » The Respiratory System » Gas Exchange across Respiratory Surfaces

# Summarizing Gas Exchange Across Respiratory Surfaces

## Summary

The lungs can hold a large volume of air, but they are not usually filled to maximal capacity. Lung volume measurements include tidal volume, expiratory reserve volume, inspiratory reserve volume, and residual volume. The sum of these equals the total lung capacity. Gas movement into or out of the lungs is dependent on the pressure of the gas. Air is a mixture of gases; therefore, the partial pressure of each gas can be calculated to determine how the gas will flow in the lung. The difference between the partial pressure of the gas in the air drives oxygen into the tissues and carbon dioxide out of the body.

## Glossary

### alveolar $${\text{P}}_{{\text{O}}_{\text{2}}}$$

partial pressure of oxygen in the alveoli (usually around 100 mmHg)

### expiratory reserve volume (ERV)

amount of additional air that can be exhaled after a normal exhalation

### FEV1/FVC ratio

ratio of how much air can be forced out of the lung in one second to the total amount that is forced out of the lung; a measurement of lung function that can be used to detect disease states

### forced expiratory volume (FEV)

(also, forced vital capacity) measure of how much air can be forced out of the lung from maximal inspiration over a specific amount of time

### functional residual capacity (FRC)

expiratory reserve volume plus residual volume

### inspiratory capacity (IC)

tidal volume plus inspiratory reserve volume

### inspiratory reserve volume (IRV)

amount of additional air that can be inspired after a normal inhalation

### lung capacity

measurement of two or more lung volumes (how much air can be inhaled from the end of an expiration to maximal capacity)

### lung volume

measurement of air for one lung function (normal inhalation or exhalation)

### partial pressure

amount of pressure exerted by one gas within a mixture of gases

### residual volume (RV)

amount of air remaining in the lung after a maximal expiration

### respiratory quotient (RQ)

ratio of carbon dioxide production to each oxygen molecule consumed

### spirometry

method to measure lung volumes and to diagnose lung diseases

### tidal volume (TV)

amount of air that is inspired and expired during normal breathing

### total lung capacity (TLC)

sum of the residual volume, expiratory reserve volume, tidal volume, and inspiratory reserve volume

### venous $${\text{P}}_{{\text{CO}}_{\text{2}}}$$

partial pressure of carbon dioxide in the veins (40 mm Hg in the pulmonary veins)

### venous $${\text{P}}_{{\text{O}}_{\text{2}}}$$

partial pressure of oxygen in the veins (100 mm Hg in the pulmonary veins)

### vital capacity (VC)

sum of the expiratory reserve volume, tidal volume, and inspiratory reserve volume

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