Blood vessels form the living system of tubes that carry blood both to and from the heart. All cells in the body need oxygen and the vital nutrients found in the blood. Without oxygen and these nutrients, the cells will die. The heart helps to provide oxygen and nutrients to the body's tissues and organs by ensuring a rich supply of blood.
Not only do blood vessels carry oxygen and nutrients, but they also transport carbon dioxide and waste products away from our cells. Carbon dioxide is passed out of the body by the lungs; most of the other waste products are disposed of by the kidneys. Blood also transports heat around your body.
The heart is a fist-sized organ that lies within the chest behind the breastbone (sternum). The heart sits on the main muscle of breathing (the diaphragm), which is found beneath the lungs. The heart is considered to have two 'sides' - the right side and the left side.
The heart has four chambers - an atrium and a ventricle on each side. The atria are both supplied by large blood vessels that bring blood to the heart. Atria have special valves that open into the ventricles. The ventricles also have valves but, in this case, they open into blood vessels. The walls of the heart chambers are made mainly of the special heart muscle. The different sections of the heart have to squeeze (contract) in the correct order for the heart to pump blood efficiently with each heartbeat.
Your blood vessels also play a part in the regulation of your blood pressure. Certain chemicals in the body can cause our blood vessels either to tighten (contract) or to relax (dilate). Signals from our nervous system can also make our blood vessels relax or contract. These changes cause a change in the size of the lumen of the vessel. This is the space through which blood flows. In simple terms, constriction of blood vessels causes an increase in blood pressure. Dilation of blood vessels causes a decrease in blood pressure. However, blood vessels don't just control blood pressure by themselves. Your body controls blood pressure using a complicated system. This involves hormones, signals from your brain and nervous system, and the natural responses of your blood vessels.