Physical Principles Governing Gas Exchange

Dalton's Law states that in a mixture of gases, each gas exerts its own pressure independently, called partial pressure. The total pressure equals the sum of individual gas pressures. Partial pressure is calculated by multiplying the gas's percent concentration by the total mixture pressure. This principle explains how oxygen, nitrogen, and carbon dioxide behave in inhaled air and move between lungs, blood, and cells based on their pressure gradients.

Henry's Law states that the quantity of gas dissolving in a liquid is proportional to its partial pressure and solubility. Blood retains more carbon dioxide than oxygen because CO2 has higher solubility. Nitrogen has minimal bodily impact due to its low solubility in blood. Temperature also affects how much gas dissolves at any given partial pressure, influencing gas exchange efficiency in lungs and tissues.

External respiration occurs in the lungs, where oxygen diffuses into blood and carbon dioxide exits. Internal respiration happens in body tissues, where gases move in opposite directions: oxygen leaves blood and carbon dioxide enters it. Both processes rely on partial pressure gradients established by Dalton's Law, allowing gases to move from high-pressure to low-pressure regions.

Gas diffusion relies on partial pressure gradients, moving from high-pressure regions to low-pressure regions. In the lungs, oxygen's higher partial pressure in air drives it into blood with lower oxygen pressure. Conversely, carbon dioxide's higher partial pressure in blood drives it into lung air. This gradient-driven movement occurs between air, lungs, blood vessels, and cells throughout the respiratory process.

Carbon dioxide has inherently higher solubility in blood compared to oxygen, allowing blood to retain more CO2 molecules at the same partial pressure. This difference in solubility, governed by Henry's Law, means CO2 dissolves more readily in body fluids. The greater CO2 solubility enables efficient carbon dioxide transport from tissues back to the lungs for exhalation during respiration.

Hyperbaric oxygen chambers contain oxygen at pressures higher than 1 atmosphere, forcing more oxygen into patients' blood according to Henry's Law. By increasing the partial pressure of oxygen in contact with blood, more oxygen dissolves into the liquid. This application treats carbon monoxide poisoning by displacing CO from hemoglobin and increasing dissolved oxygen available to tissues.

Temperature affects how much gas dissolves in blood at any given partial pressure, according to Henry's Law. Warmer body tissues and blood generally allow less gas to dissolve, while cooler conditions permit greater dissolution. This temperature-dependent solubility influences the efficiency of oxygen and carbon dioxide exchange between blood and tissues throughout the body.