Controls
The cardiac, or heart, muscle pumps blood through the body, where it follows a cycle. Pulmonary arteries branching out from the heart take blood to the lungs, where it is oxygenated. From there, the blood travels through arteries throughout the body, and is then returned, deoxygentated, back to the heart, and once again to the lungs for more oxygen. This process takes place every second of every day of a person's life until the heart stops. Blood pressure is a measurement of how much force the heart uses to pump the blood through the heart muscle and into the body. However, blood pressure is not regulated by the heart itself, as many may think, but the brain.
Brain Impulses
Blood pressure is controlled by the brain, which in turn tells the heart what to do via nerve impulses and signals. Blood pressure signals are sent to the brain by baroreceptors in the carotid artery, the artery found in the neck. These receptors constantly monitor the dilation or distension of artery walls, caused by pressure of blood traveling through them. Blood pressure may alter depending on whether a person is laying down, standing, exercising or afraid.
Sympathetic Nervous System
The baroreceptors send nerve impulse messages from the carotid artery through the Vagus nerve, which connects to the lower part of the brain stem. Depending on the pressure inside the carotid, the Vagus nerve alerts the brain stem to what is going on, and the brain stem transmits signals to the sympathetic nervous system, which controls breathing, heart rate and other mechanisms in the body.
Processing
The impulses sent to the sympathetic nervous system automatically cause blood vessels to constrict. At the same time, the adrenal medulla (a bundle of nerve-type tissues) found on the tips of the kidneys release a chemical called adrenaline into the bloodstream. The adrenal medulla and the brain stem work together to raise or lower blood pressure according to need, much as an internal barometer to regulate pressure whether a person is lying down, sleeping or running in fear.
