Final answer:
The hypothesized response of the human respiratory and circulatory systems to decreased oxygen levels is an increased heart rate and breathing rate. This is due to the activation of chemoreceptors that stimulate the cardiovascular and respiratory systems to work together to maintain homeostasis.
Step-by-step explanation:
When considering how the human respiratory and circulatory systems will respond to a change in the environment, such as decreased oxygen levels or increased physical activity, both systems work in tandem to increase the supply of oxygen and remove carbon dioxide. A correct hypothesis would be that there will be an increased heart rate and breathing rate in response to decreased oxygen levels. This is a physiological adjustment to ensure that the cells of the body maintain their metabolic functions efficiently.
Central and peripheral chemoreceptors monitor the levels of CO2, O2, and pH in the blood and stimulate the respiratory centers in the brain to adjust the rate and depth of breathing. As a response, the respiratory system increases ventilation through hyperpnea, which is the increase in the rate and depth of ventilation. Simultaneously, the cardiovascular system increases cardiac output and constricts peripheral vessels to distribute the needed oxygen throughout the body efficiently.
During increased oxygen demand, such as during exercise, a similar response is activated with hyperpnea initiating upon the start of the exercise, thus increasing oxygen supply and removing excess CO2. This shows how closely the respiratory and circulatory systems work together to maintain homeostasis within the body under changing environmental conditions.