Parts of the Cardiovascular System


Your heart is a muscle that is about the size of your fist. It is located just left of the center of your chest, behind your rib cage. The human heart has four chambers.The two upper, smaller chambers are called the right and left atria (singular: atrium). Beneath the atria, the two larger chambers are called the right and left ventricles. For proper flow, it is very important that your blood moves in only one direction. Valves between the chambers of your heart are the gatekeepers that prevent blood from going backwards.


The atria and ventricles are separated by a pair of one-way valves, known as the mitral (or the bicuspid) and tricuspid valves. The pulmonary and aortic valves also connect your heart to the pulmonary and aortic blood vessels that carry blood away from your heart. The closing of the valves in your heart makes the classic "lub" and "dub" sounds that you hear when you use a stethoscope to listen to your heartbeat.

Blood Vessels   

Your heart is connected to the rest of your body through a series of arteries, veins, and capillaries, collectively known as blood vessels.  


Arteries carry blood away from your heart. They have thick walls made up of lots of smooth muscle cells so they can handle and help regulate the pressure and velocity at which your blood circulates through your body. 


Veins carry blood to your heart. The pressure of this returning blood is very low so their walls have fewer smooth muscle cells and are much thinner than arteries. They have valves in them to help keep the blood traveling in only one direction.


Capillaries are tiny blood vessels that connect the arteries and veins. Their walls are very thin, composed of just one single layer of cells.  This layer allows for the exchange of fluid, nutrients, and other small molecules between the blood and your body’s tissues. The blood in capillaries has a much lower velocity to allow time for the movement of fluid and nutrients. 


Your blood is made of red blood cells, white blood cells, platelets, and plasma. 

Red Blood Cells

Red blood cells are responsible for collecting oxygen from your lungs and delivering it to all parts of your body as well as carrying waste products to your kidneys so they may be removed from your body.  Red blood cells get their color from the protein hemoglobin that contains iron. When the iron group in the protein (also called the heme group) binds oxygen, the protein appears brighter red. 

White Blood Cells

White blood cells are part of your immune system and help your body fight infection. 


Platelets help blood clots form to stop bleeding when an injury, like a cut, has occurred. 


The liquid part of your blood is called plasma and consists mostly of water. Diluted in the water are sugars, minerals, proteins, molecules that help blood clot, hormones, and carbon dioxide waste.