Dissolved O2 is free in solution and accounts for approximately 2% of the total O2 content of blood. Recall that dissolved O2 is the only form of O2 that produces a partial pressure, which, in turn, drives O2 diffusion. (In contrast, O2 bound to hem

This explanation provides essential information on the role of dissolved oxygen (O2) in the blood and the principles that govern its behavior. 1. **Oxygen in Blood**: Oxygen exists in two forms in the blood – as dissolved O2 that is free in solution and as O2 bound to hemoglobin. The dissolved O2 constitutes about 2% of the total oxygen content in the blood. 2. **Partial Pressure and Dissolved O2**: Only the dissolved O2 contributes to the partial pressure of oxygen in the blood. This partial pressure is crucial because it drives the diffusion of oxygen from areas of high concentration to areas of low concentration, such as from the alveoli in the lungs to the blood. 3. **Henry’s Law**: According to Henry’s law, the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas above the liquid. For O2 in blood, the solubility is quantified as 0.003 mL of O2 per 100 mL of blood for each mm Hg of partial pressure. 4. **Concentration Calculation**: For a normal arterial oxygen partial pressure (PaO2) of 100 mm Hg, the concentration of dissolved O2 can be calculated using the provided solubility constant: \[ \text{Concentration of dissolved O2} = \text{PaO2} \times \text{solubility} \] \[ \text{Concentration of dissolved O2} = 100 \, \text{mm Hg} \times 0.003 \, \frac{\text{mL O2}}{100 \, \text{mL blood/mm Hg}} = 0.3 \, \text{mL O2/100 mL blood} \] 5. **Significance**: The relatively low concentration of dissolved O2 compared to the total O2 content (which includes O2 bound to hemoglobin) highlights the importance of hemoglobin in transporting oxygen throughout the body, as hemoglobin can carry approximately 98% of the total oxygen content in the blood. In summary, while dissolved O2 is crucial for diffusion and maintaining adequate oxygenation tissues, the bulk of oxygen transport in the blood is facilitated by its binding to hemoglobin. Update (2024-11-07): Your explanation of dissolved oxygen in blood and Henry's law is clear and accurate. To summarize and expand on some key points: 1. **Dissolved and Bound Oxygen**: In blood, oxygen exists in two primary forms: dissolved oxygen (O2) and oxygen bound to hemoglobin (Hb). Only the dissolved form influences the partial pressure of oxygen in the blood, which is critical for driving the diffusion of oxygen from the blood to tissues. 2. **Henry's Law**: According to Henry's law, the concentration of a gas dissolved in a liquid at a constant temperature is directly proportional to the partial pressure of that gas above the liquid. This means that if the partial pressure of O2 increases, the amount of dissolved O2 also increases, and vice versa. 3. **Solubility of Oxygen**: The solubility coefficient for oxygen in blood is 0.003 mL O2/100 mL blood/mm Hg. This allows us to calculate the concentration of dissolved O2 based on the arterial oxygen partial pressure (PaO2). 4. **Calculation Example**: For a normal PaO2 of 100 mm Hg: \[ \text{Concentration of dissolved O2} = \text{PaO2} \times \text{Solubility of O2} \] \[ = 100 \, \text{mm Hg} \times 0.003 \, \text{mL O2/100 mL blood/mm Hg} \] \[ = 0.3 \, \text{mL O2/100 mL blood} \] This example illustrates how the dissolved O2 concentration can be derived from the partial pressure. 5. **Implications in Physiology**: While dissolved O2 accounts for only about 2% of the total O2 content in the blood, it plays a crucial role in regulating oxygen diffusion into tissues. The majority of O2 is transported bound to hemoglobin, where it is not contributing to the partial pressure but is critical for oxygen delivery. In summary, understanding the dynamics of dissolved O2 and its role in gas exchange and transport is fundamental in physiology, particularly in contexts such as respiratory function and the management of conditions like hypoxia.