Final answer:
Heart rate and respiratory rate increase when a person moves from sitting to standing to marching due to the need to maintain blood flow and oxygen supply. Age, fitness levels, and exercise can affect heart rates, and during exercise, cardiac output initially rises with heart rate and then begins to decrease as stroke volume falls.
Step-by-step explanation:
When a person goes from sitting to standing to marching, their heart rate (HR) and respiratory rate typically increase. This physiological response is due to the needs of the cardiovascular and respiratory systems to maintain adequate blood flow and oxygen supply to the muscles and brain. Upon standing, the body must counteract gravity to maintain blood pressure, which is achieved by increasing the HR. Marching involves muscle activity, which requires more oxygen and produces more carbon dioxide, necessitating an increase in both HR and the depth of breathing. The HR and respiratory rate are regulated by the cardiovascular centers in the medulla oblongata that respond to various stimuli, including changes in blood pressure and carbon dioxide levels.
Different factors can affect HR, including age, fitness levels, and exercise. For instance, newborns have a higher resting HR, which decreases in young adulthood. During exercise, the rate of blood returning to the heart increases, leading to an increased HR and stroke volume (SV). Initially, as HR increases, cardiac output (CO) will rise, but as HR continues to increase without sufficient ventricular filling time, SV, and eventually CO, will begin to decrease.