There are blood pressure sensors throughout your body. When you begin to use excessive amounts of oxygen, the brain is the first to notice, as it requires more than any other organ in the body, and is extremely sensitive to this.
Once it realizes it needs more oxygen, it sends a message to the heart saying “hey, check blood pressure sensors & raise blood pressure if needed”. Then, by order of the hypothalamus (the brain), a cascade of hormones is sent to the pituitary & then the heart, where the heart will increase cardiac output & dilate or constrict arteries & arterioles where appropriate.
Latest Answers