A peek at the secret life of your heart  

Your heart and a 60,000-mile network of blood vessels make up your cardiovascular system. Well, it would be that long if you stretched out all those vessels end to end.

Your heart is responsible for the main function of your cardiovascular system: pumping blood through this vast network to all of the tissues and organs of your body, a process called circulation.

Think of the circulatory process as a figure eight. In one loop, blood circulates between your heart and lungs (pulmonary circulation). In the other, blood circulates between your heart and the rest of your body (systemic circulation). These two loops interact to pump blood in a continuous circuit: heart to body, body to heart, heart to lungs, lungs to heart, and heart to body.

How your heart works to pump blood and vital nutrients throughout your body.


Where is the heart ?

Your heart is a muscular organ located slightly to the left of the center of your chest not to the far left, as is sometimes thought. Your heart isn't quite shaped like a valentine, either. It's actually shaped like an inverted cone. The tip (apex) is at the bottom and the wider part at the top. Your heart sits at an angle in your chest, with the apex pointing to the left.

Your heart is protected by your breastbone (sternum) in the front and your spinal column in the back, plus your lungs and rib cage. The average adult heart is about the size of a clenched fist and weighs about 12 ounces


How  many layers ?

The muscular wall of the heart has three layers:

Endocardium. The thin inner layer that covers the inside surfaces of your heart's four chambers, valves and muscles.

Myocardium. The thick middle layer of the heart muscle. It's the workhorse, responsible for most of the heart's pumping action.

Epicardium. The thin, glossy membrane that covers the outer surface of the heart.

In addition, a protective sac called the pericardium encases the entire heart




The chambers

Circulation is a continuous process, and your heart, lungs and the rest of your body have a constant supply of blood coming and going. Various structures in your heart regulate those comings and goings.

Your heart is divided into two sides, left and right. Each side has two chambers, or open spaces, for a total of four. The four chambers are the left atrium and right atrium near the top of the heart, plus the left ventricle and right ventricle near the bottom. The right side of the heart is responsible for pulmonary circulation, while the left side forms the circulatory loop that supplies blood to the rest of your body.


Nourishing the heart

In addition, the heart muscle needs its own supply of blood. Two branches of the aorta lead to the right and left coronary arteries. Those arteries extend over the surface of the heart and branch into smaller capillaries. The capillaries supply blood to the heart for its own nourishment. The capillaries drain into two coronary veins that empty into the right atrium


Valves: The heart's gatekeepers

Valves within your heart make sure blood flows in the right direction. They function much like gates: They open only when they're pushed on, and they open only one way. The heart has four valves: the tricuspid, mitral, pulmonary and aortic. Each opens and closes once per heartbeat or about once every second.

The pulmonary circulation loop starts with the blood sitting in your heart's right atrium. From that atrium, blood flows through the tricuspid valve into the right ventricle.


Into the lungs

The tricuspid valve allows blood into the right ventricle. When filled with blood, the ventricle then contracts, forcing blood out much like squeezing ketchup out of a soft bottle. Contraction, known as systole (SIS-to-le), forces blood from one area of your heart to another.

Contraction of the right ventricle forces the tricuspid valve to close and the pulmonary valve to open. With the pulmonary valve open, blood can flow into the pulmonary artery. The pulmonary artery branches into two vessels, one that carries blood to the left lung and one that carries blood to the right lung.


Picking up oxygen

Once in the lungs, the blood gives up carbon dioxide gas. The gas passes through tiny air sacs into bronchioles tubes that carry air into and out of the lungs and you exhale the carbon dioxide.

When you breathe in, your lungs get a supply of oxygen. Red blood cells in your blood pick up that oxygen, turning your blood bright red. The tissues and organs of your body need oxygen to function, and your blood carries it to them


Back to the heart

The blood needs to get out of your lungs so it can distribute that oxygen. Each lung has two pulmonary veins. The veins carry that newly oxygenated blood back to your heart, delivering it to the left atrium, where it can begin the journey to the rest of your body.

Arteries, veins, capillaries all of these vessels may get confusing, but each has its own role. Arteries carry blood away from the heart. Veins carry blood back to the heart, whether from the lungs or other parts of your body, from head to toe. Capillaries are the go-between, transporting blood from arteries to veins and through which nutrients enter tissues and waste products are picked up.



Into the left ventricle

With blood in the left atrium, the heart relaxes the opposite of contraction. This phase is called diastole (di-AS-to-le). The relaxation forces blood from the atrium, pushing it against the mitral and tricuspid valves the gates which open and allow blood into the left ventricle.

The cycle of contraction and relaxation causes blood flow to be pulsatile it pulsates, or beats rhythmically. You can often feel your heart beating by placing your hand on the left side of your chest. The pulsation is also transmitted to your blood vessels, so you can feel your pulse where large arteries are close to the surface of your body, such as your wrist, your neck and your groin. The period from the beginning of one heartbeat to the beginning of the next is the cardiac cycle.




The Electrical system

All this beating of your heart wouldn't be possible, though, without some electricity. Like your home, your heart has an electrical (conduction) system. The conduction system carries electrical impulses throughout your heart, causing it to beat.

Impulses begin in the sinus node, high in the right atrium. They travel through the atrial pathways to the atrioventricular node. There, the signals briefly slow down as they're funneled into the electrical network of the ventricles, called the His-Purkinje (hiz-pur-KIN-je) system. The conduction system permits the electrical impulse to reach all parts of your heart at the right time, so that the heartbeat is coordinated and occurs at a normal rate. Your heart's electrical activity can be recorded on an electrocardiogram (ECG).



Into the aorta

With blood in it, the left ventricle then contracts again beginning the systolic portion of the cardiac cycle. That forces the mitral valve to close while opening the aortic valve. With the aortic valve open, blood can flow freely into the aorta.

The aorta, or main artery, is the largest blood vessel in your body. It has numerous branches to supply various parts of your body with blood. The branches of the carotid artery, for instance, travel in your neck to supply your brain with blood. The aorta also turns downward, supplying blood vessels to your abdomen. It splits into more arteries, supplying the legs with blood.


Starting over again

Your blood transports more than just oxygen and carbon dioxide. It also carries hormones from endocrine glands, for instance, making sure they wind up in the right places. Waste products other than carbon dioxide go to your kidneys and liver, where they can be removed or broken down. Blood also picks up nutrients from your intestines and carries them to your liver and other parts of your body.

Your tissues and organs absorb oxygen and the other nutrients from blood. Depleted blood then flows back to the heart, through a network of veins, to become replenished. The large veins that enter the heart are the superior vena cava and the inferior vena cava. And the circulatory process starts anew. Actually, there's no beginning or end to circulation. It's a continuous and efficient process to supply your body with all of the nutrients it needs to function normally without even thinking about it.