During exercise, the cardiovascular system must supply muscles with large amounts of oxygen and fuel and get rid of a lot of wastes. How do the cardiovascular systems of athletes respond to prolonged exercise? When athletes exercise, what is the primary physiological variable responsible for their sustained increase in ventilation rate? a. decreased blood PO2 b. increased blood PCO2 c. increased blood pH d. increased body temperature

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1. The cardiovascular system of athletes adapts to prolonged exercise by increasing cardiac output (the amount of blood the heart pumps per minute) and redistributing blood flow to the muscles. This is achieved through an increase in heart rate and stroke volume (the amount of blood pumped per heartbeat).
2. During exercise, the blood vessels in the muscles dilate, allowing for increased blood flow to these areas. This process is known as vasodilation and is crucial for delivering oxygen and nutrients to working muscles while removing carbon dioxide and other metabolic wastes.
3. The cardiovascular adaptations also include an increase in the total volume of blood, which enhances the oxygen-carrying capacity of the blood, providing more oxygen to the muscles.
4. The primary physiological variable responsible for the sustained increase in ventilation rate during exercise in athletes is 'b. increased blood PCO2'. As exercise intensity increases, the muscles produce more carbon dioxide as a byproduct of metabolism, which leads to an increase in blood PCO2 levels.
5. The increase in blood PCO2 stimulates chemoreceptors in the body to signal the respiratory center in the brain, leading to an increase in the rate and depth of breathing. This process is known as hyperpnea and helps to expel the excess CO2 and maintain blood pH levels.