Question

multiple choice question
why do normal fluctuations in blood oxygen levels have little influence on respiratory control?
systemic venous blood is still 75% saturated, so oxygen is still abundant.
oxygen in venous blood is unable to bind to the peripheral chemoreceptors.
oxygen levels do not have an effect on blood ph and, thus, does not need to be controlled.

Explanation:

• Option 1: Systemic venous blood is about 75% saturated with oxygen even after delivering oxygen to tissues. So, normal fluctuations in blood oxygen levels (within a certain range) don't severely impact the overall oxygen - carrying capacity. The body has a reserve, and this reserve means that small changes in oxygen levels (normal fluctuations) don't trigger major respiratory control changes.
• Option 2: Oxygen in venous blood can bind to peripheral chemoreceptors. Peripheral chemoreceptors (like the carotid and aortic bodies) are sensitive to oxygen levels (among other things like pH and carbon - dioxide levels). So, this option is incorrect.
• Option 3: Oxygen levels can indirectly affect blood pH. For example, when oxygen levels are very low, anaerobic metabolism can occur, leading to the production of lactic acid which can lower blood pH. Also, respiratory control is not solely based on pH - oxygen levels can directly influence chemoreceptors. So, this option is incorrect.

Answer:

Systemic venous blood is still 75% saturated, so oxygen is still abundant.