Pulmonary 3 Gas Exchange

Summary

This lecture delves into the fundamentals of pulmonary physiology, focusing on oxygen supply's dependency on ambient air concentration and pressure. It explains the constant composition of ambient air, the concept of partial pressure, and Dalton's law. The script further explores gas behavior, Henry's law, and the passive diffusion of gases between the lungs, blood, and body tissues, emphasizing the role of pressure gradients and gas solubility in efficient gas exchange, crucial for understanding respiratory processes and maintaining life.

Takeaways

• 🌍 Oxygen supply to the body is critically dependent on the concentration of oxygen in the ambient air and the pressure it exerts.
• 📊 Ambient air composition is remarkably constant, with oxygen at about 20.93%, nitrogen at 79.4%, and carbon dioxide at 0.03%, with trace amounts of water vapor.
• 💨 Gas molecules are in constant rapid motion, causing collisions that generate pressure, which is essential for the diffusion of gases across respiratory surfaces.
• 🌡 Partial pressure of a single gas is a product of its concentration and the total pressure, exemplified by oxygen's partial pressure at sea level being 150.9 mm of mercury.
• 🔍 Dalton's law states that the total pressure of a gas mixture is the sum of the partial pressures of the individual gases.
• 🌬 The partial pressure of oxygen decreases as it moves down the respiratory tract due to the saturation with water vapor.
• 🔄 Henry's law explains that the amount of gas dissolved in a fluid is directly proportional to the pressure of the gas over the fluid, influenced by the pressure differential and solubility of the gas.
• 🔄 Gas solubility varies, affecting the amount transported; for instance, carbon dioxide is approximately 25 times more soluble than oxygen under the same conditions.
• 🌀 Gas diffusion occurs only when there is a pressure difference, with the partial pressure gradient being the driving force.
• 🏃‍♂️ During exercise, the pressure of oxygen in active muscle can drop significantly, creating a larger pressure differential for oxygen to diffuse into cells and carbon dioxide to move out.
• 🔄 Gas exchange in the body occurs passively by diffusion, with pressure gradients determining the direction of gas movement between the lungs and blood, and at the tissue level.

Q & A

What are the two critical factors for oxygen supply to the body?

The two critical factors for oxygen supply to the body are the concentration of oxygen in the ambient air and the pressure that this air exerts.

What are the approximate percentages of the main components in the ambient air?

Oxygen makes up about 20.93%, nitrogen is the most abundant at 79.4%, and carbon dioxide is present at a much lower concentration of 0.03%. There are also small quantities of water vapor.

What is the concept of partial pressure in relation to gases?

Partial pressure refers to the pressure exerted by a single gas in a mixture of gases. It is a combination of the gas's concentration and the total pressure of the mixture.

How does the partial pressure of oxygen at sea level compare to the total atmospheric pressure?

At sea level, the total atmospheric pressure is approximately 760 mm of mercury. The oxygen partial pressure is calculated as 760 mm * 20.93%, which equals about 150.9 mm of mercury.

What is Dalton's law and how does it relate to the total pressure of the atmosphere?

Dalton's law states that the total pressure of a mixture of gases is the sum of the partial pressures of the individual gases. It helps to calculate the total pressure of the atmosphere at sea level.

How does the humidification of air affect the partial pressure of oxygen in the tracheal air?

Humidification of air, which occurs as air enters the nasal cavities and mouth and passes down the respiratory tract, decreases the partial pressure of oxygen in tracheal air by about 10 mm of mercury, from 159 mm to 149 mm.

What is Henry's law and how does it explain the movement of gases between air and fluids?

Henry's law states that the amount of a specific gas dissolved in a fluid at a given temperature is directly proportional to the pressure of the gas over the liquid. It explains how the pressure differential and the solubility of the gas affect the gas movement between air and fluids.

How does the solubility of a gas affect the efficiency of gas exchange processes?

The solubility of a gas affects the efficiency of gas exchange processes by determining how much of the gas can be transported. A gas with greater solubility will have a higher concentration in the fluid at a given pressure, leading to more efficient gas exchange.

What factors account for the dilution of oxygen in inspired air as it passes into the alveola chambers?

The dilution of oxygen in inspired air as it passes into the alveola chambers is accounted for by three factors: water vapor saturation of the dry inspired air, oxygen continually leaving the alveola, and carbon dioxide continually entering the alveola.

How does the pressure gradient of gases facilitate the passive exchange of gases between the lungs and blood?

The pressure gradient of gases facilitates the passive exchange of gases between the lungs and blood by creating a diffusion gradient. Oxygen diffuses from areas of higher pressure in the alveola air to areas of lower pressure in the blood, and carbon dioxide diffuses in the opposite direction.

What changes occur in the gas pressures of arterial blood and tissues during vigorous exercise?

During vigorous exercise, the pressure of oxygen molecules in active muscle can drop to as low as 3 mm of mercury, while carbon dioxide pressure can approach 90 mm of mercury, creating a substantial pressure differential that drives the diffusion of oxygen to the cells and carbon dioxide away from the cells.