Mastering Partial Pressure

Gas Composition and Partial Pressure

• Nitrogen contributes the most to the partial pressure in the air we breathe.
• The partial pressure of oxygen in the air we breathe is approximately 160 mmHg.
• Dalton's Law states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas.

Gas Solubility and Diffusion

• Henry's Law states that the partial pressure of a gas dissolved in a liquid will be the same as the partial pressure of gas in contact with the liquid at equilibrium.
• Fick's Law states that the volume of diffused gas is dependent on the diffusion gradient, surface area, membrane thickness, and diffusion coefficient.
• Graham's Law states that the gas diffusion rate is inversely proportional to the square root of its gram molecular weight.
• Carbon dioxide has a greater solubility in water than oxygen.
• When the partial pressure of the gas decreases, the amount of dissolved gas in a liquid also decreases.

Gas Exchange in the Respiratory System

• Nitrogen has the highest percentage in atmospheric air.
• Oxygen shows a significant decrease in concentration from atmospheric air to alveolar air.
• Carbon dioxide shows an increase in concentration from humidified air in the trachea/bronchi to alveolar air.
• Carbon dioxide shows a decrease in concentration from alveolar air to expired air.
• Nitrogen shows the least variation in concentration throughout the airways and respiratory cycle.
• Conditions that cause a decrease in the partial pressure of oxygen in arterial blood include high altitude, anemia, and lung disease.
• Conditions that cause an increase in the partial pressure of carbon dioxide in alveoli include hypoventilation and respiratory acidosis.
• Conditions that compromise the efficiency of gaseous exchange in alveoli include lung fibrosis, pneumonia, and emphysema.

Alveolar Gas Exchange

• During normal respiration and resting conditions, approximately 10% of the volume of gas in the alveoli is replaced during inspiration.
• During hypoventilation, the partial pressure of carbon dioxide in alveoli increases, and the partial pressure of oxygen in alveoli decreases.

Diffusion of Gases

• In lung fibrosis, the structure responsible for slowing down the diffusion of oxygen is the thickened alveolar-capillary membrane.
• Carbon dioxide diffuses 20 times faster than oxygen in the alveoli.
• Conditions that can lead to a decrease in the gaseous exchange of oxygen and carbon dioxide in the alveoli include lung fibrosis, pneumonia, and emphysema.
• In lung fibrosis, oxygen diffusion gets slowed down in the step of diffusion across the alveolar-capillary membrane.
• The component that is not part of the diffusion steps across the pulmonary blood gas barrier is the plasma compartment.
• Surfactant plays a role in the gaseous exchange process in alveoli by reducing the surface tension of water and increasing the surface area for gas exchange.
• Dissolved gas enters the blood plasma after crossing the endothelial cells in the gaseous exchange process.
• Dissolved gas enters and binds with hemoglobin after crossing the plasma compartment.

Gas Diffusion and Solubility

• The diffusion coefficient determines the volume of diffused gas according to Fick's Law of diffusion.
• Carbon dioxide has a higher partial pressure difference in the alveoli and tissues area.
• The relative diffusion rate of oxygen compared to carbon dioxide in a gaseous medium is 1:20.
• Carbon dioxide is approximately 20-25 times more soluble than oxygen in water.