Hey ysitu, welcome
The sympathetic division of the nervous system becomes very active in response to stressful or startling stimuli (in your case, exercise). While the animal?s motor neurons are stimulating skeletal muscles to contract during exercise, the sympathetic drive is increasing heart rate and breathing rate. Additionally, blood vessels going toward skeletal muscles will dilate to ensure an adequate supply of oxygen and nutrients. At the same time, the sympathetic drive stimulates the adrenal medulla (an organ near your right kidney) to release
epinephrine into the bloodstream. This will also increase heart and respiratory rates. The nervous system also stimulates
glucagon release and inhibits insulin release to maintain high plasma levels of glucose. The high plasma glucose levels will be enhanced by the release of glucocorticoids from the adrenal cortex.
The hormone
glucagon stimulates gluconeogenesis in the liver and stimulates the release of free fatty acids to use it as a fuel, instead of glucose, in the other two process of cellular respiration (Krebs Cycle and electron transport chain) to produce energy, by doing so, it conserves and produce glucose at the same time; therefore raising the blood sugar level when it is low. It shows a negative feedback because the response negates the stimulus to maintain homeostasis.
Moreover, your body needs oxygen in order to efficiently break down glucose and process it into your cell's primary energy source (ATP). As you do more intense exercise, you need more energy and therefore more oxygen. Your blood carries oxygen from the lungs to your muscles. To keep up with these increased oxygen needs, you have to have more blood going to your muscles. As a result, your heart pumps faster, sending more oxygenated blood to your muscles per second. This cannot be done without the aforementioned explanation above (i.e. the release of several different types of hormones from different organs in your body). Similarly, during exercise, blood sugar levels are often low. Thus, to maximize glucose uptake by cells, insulin is produced by the pancreas. When cells take up glucose from the blood, this makes the glucose level go down. When you stop exercise, the cells being worked out don't need as much glucose anymore. The pancreas sees an increase in blood glucose and stops making insulin. When the pancreas stops sending this message (insulin), the cells in the body stop taking extra glucose out of the blood. This is also an example of negative feedback during exercise.
In my undergrad. we did a study like this and found that physical exercise also stimulates the body’s core
temperature, which functions as a major factor driving active sympathetic vasodilator activity. Scientists are also convinced that the increase in heart rate can be due to muscle-derived metabolites (adenosine, potassium), and flow-mediated vasodilators (nitric oxide) – all of which might contribute to vasodilation
of vascular smooth muscle.
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