Final answer:
During exercise, skeletal muscles consume oxygen to produce ATP, resulting in lower oxygen concentration in the blood leaving the muscles compared to the blood leaving the lungs due to increased oxygen uptake and utilization by muscle tissue.
Step-by-step explanation:
The discrepancy in oxygen levels between blood leaving the lungs and blood leaving the skeletal muscles during exercise is due to various physiological factors. During exercise, skeletal muscles consume more oxygen to produce adenosine triphosphate (ATP), which is the energy currency for muscle contractions. This increased demand for oxygen leads to a lower concentration of oxygen in the blood exiting the muscles, as it has been used for energy production. Additionally, the oxygen-hemoglobin dissociation curve facilitates more oxygen to be released to the active tissues where it's needed most. Muscle activity also generates by-products such as lactic acid, which further stimulates oxygen release from hemoglobin. Furthermore, capillary beds within the muscles open wider during exercise to increase blood flow and deliver more oxygen to meet the heightened demand. As a result, the blood that leaves the exercised skeletal muscles is lower in oxygen concentration compared to when it left the lungs, reflecting the consumption and utilization of oxygen by the muscle tissue.