Final answer:
Net diffusion of oxygen will occur from the blood with PO2 of 90 mmHg to the systemic tissue with PO2 of 40 mmHg, driven by the partial pressure gradient. Oxygen moves from areas of higher to lower PO2 as it binds and dissociates from hemoglobin based on tissue demands.
Step-by-step explanation:
When considering the diffusion of oxygen in the human body, partial pressure gradients play a crucial role. If the partial pressure of oxygen (PO2) in the blood is 90 mmHg and the PO2 in systemic tissue is 40 mmHg, there would be a net diffusion of oxygen from the blood into the tissues. This is because oxygen moves down its pressure gradient, leaving areas of higher partial pressure (blood) to areas of lower partial pressure (tissue).
In the systemic capillaries, where the blood has a higher concentration of oxygen, oxygen diffuses out to the surrounding tissues that have a lower concentration. This process is a part of external respiration, which occurs in the lungs where blood takes up oxygen. In contrast, during cellular respiration, tissues use oxygen, which reduces their PO2, making them sites where oxygen will diffuse into to maintain cellular function.
Additionally, the oxygen-hemoglobin saturation/dissociation curve ensures that tissues with higher metabolic demands receive more oxygen due to a more significant drop in their PO2, which causes more oxygen to dissociate from hemoglobin and become available to cells.