Final answer:
In a crosscurrent gas exchange system, the oxygen partial pressure of the excurrent blood is higher than that of the excurrent air or water, thanks to the perpendicular flow of blood across the gas exchange surface. Gas exchange is guided by Dalton's law and Henry's law, causing oxygen to transfer from areas of high to low partial pressure, and even though carbon dioxide has a smaller partial pressure gradient, its high solubility facilitates its exchange.
Step-by-step explanation:
In a crosscurrent gas exchange system, the oxygen partial pressure of the excurrent blood is higher than that of the excurrent air or water. This occurs because in these systems, the blood flows across the gas exchange surface in a direction that is perpendicular to the flow of air or water. This arrangement allows the blood to absorb oxygen more efficiently compared to concurrent flow systems, where the oxygen partial pressure in blood and water would become equal when reaching equilibrium.
The behavior of gases and their exchange in the respiratory system are explained by Dalton's law and Henry's law. Dalton's law tells us that each gas in a mixture exerts its own partial pressure, while Henry's law states that the amount of gas dissolved in a liquid is proportional to its partial pressure. Oxygen molecules move down their pressure gradient, diffusing from areas of high pressure to low pressure, enabling oxygen to transfer from the higher partial pressure in the air or water to the lower partial pressure in the blood.
As for the partial pressure of carbon dioxide, it is typically higher in the pulmonary capillaries than in the alveoli, driving its diffusion into the excurrent air or water. The greater solubility of carbon dioxide compared to oxygen ensures that despite a smaller partial pressure gradient, effective gas exchange still occurs.