Human Heart: Anatomy, Function & Facts

The heart of the human body is an organ that circulates blood through the vessels of the circulatory systems. It supplies oxygen and nutrients to the tissues, and removes carbon dioxide and other pollutants.
Dr. Lawrence Phillips, a New York-based cardiologist, said that the tissues need to have a steady supply of nutrition to stay active. "If the heart is not able supply blood to the tissues and organs, they will die."

The human heart is located in central part of the chest, slightly to the left from the sternum (breastbone). According to the Texas Heart Institute, it sits between your lungs. It is enclosed in a double-walled sac called pericardium. The pericardium protects the heart and anchors it within the chest. The pericardial fluid acts between the outer layer of the parietal and inner layers, the serous, as a lubricant. The fluid helps to lubricate the heart during contractions, movements of the lungs, and diaphragm.

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What is the human heart like?

According to Henry Gray's " Anatomy of the Human Body", the human heart is approximately the same size as a large fist. It weighs between 10 and 12 ounces in men (280 and 334 grams), and between 8 and 10 pounds (230 and 228 grams) for women.

Phillips explained to Live Science that the physiology and functioning of the heart is basically dependent on "structure, electricity, and plumbing".

According to the National Institutes of Health, there are four chambers in the human heart: two chambers at the top (the atria), and two chambers at bottom (the ventricles). The "right atrium" and "right ventricle are together the "right heart," while the left atrium, left ventricle and left ventricle form the "left heart." The septum is a wall of muscle that separates the heart's two sides.

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Illustration of the inside of a human heart showing all four chambers. Image credit: Getty Images

Three layers make up the heart's outer walls. The inner wall of your pericardium is formed by the epicardium, the outermost wall layer. The muscle that contracts and expands the heart is found in the middle layer, called myocardium. According to the British Heart Foundation, the inner layer, called endocardium lines the heart chambers.

The tricuspid and mitral valves connect the upper and lower chambers. The pulmonary semi-lunar and aortic valves separate the right ventricle and pulmonary arteries, respectively. The valves are held together by chordae tendinae or the heartstrings.

How does the heart of a human being work?

Two pathways are used by the heart to circulate blood: the pulmonary and systemic circuits.

According to Biomedical Science, the pulmonary circuit is where deoxygenated blood travels from the right ventricle to the heart via the lung artery to the lungs. The oxygenated blood then returns through the vein to the left atrium.

The systemic circuit is where oxygenated blood leaves from the heart and travels through to the left ventricle to reach the aorta. From there, it enters the capillaries and arteries, where it provides oxygen for the tissues of the body. The venae vae receives deoxygenated blood and it returns to the right atrium of the heart.

Phillips explained that the heart is also a muscular organ, and therefore requires fresh oxygen and nutrients.

He said that blood leaves the heart via the aortic valve and two sets of blood vessels bring oxygenated blood to the heart muscle. On one side of the heart, the left main coronaryartery branches into the left anterior and descending arteries, as well as the left circumflex. The right coronaryartery branches off to the right of the aorta.

Phillips stated that a blockage in any one of these arteries could cause a heart attack or damage to the muscle. A heart attack is different from cardiac arrest. This is when the sudden loss of heart function is usually caused by electrical disturbances to the heart rhythm. He said that cardiac arrest can be caused by a heart attack, but it can also be caused due to other issues.

Related: Can other animals have heart attacks?

The human heart is approximately the same size as a fist. Getty Images image credit

The heart has electrical pacemaker cells that cause it to contract, producing a heartbeat.

Phillips stated that each cell has the potential to lead the group and have the whole team follow. He said that people with irregular heartbeats, also known as atrial fibrillation have every cell trying to be the leader. This causes them to beat out of tune with each other.

Five stages are required for healthy heart contraction. The heart relaxes in the first stage, called early diastole. Next, the atrium contracts (atrial synstole), to push blood into ventricle. The ventricles then contract without changing their volume. Next, the ventricles contract while empty. Finally, the ventricles stop contracting while empty and begin to relax. The cycle continues. The blood flows in one direction through the heart thanks to the valves that prevent backflow.

Your heart rate will increase by around 100,000 beats per hour (60 to 80 beats per min) by the end of the day. According to the Cleveland Clinic, this will pump approximately 1.5 gallons (6.8 liters) blood through the 60,000 miles (97,000 kilometers) of blood vessels in the human body.

Can humans get heartworm?

According to the U.S. Food and Drug Administration, heartworm is a disease that can affect pets, primarily dogs. It causes organ damage and heart failure. Dirofilaria immitis, a parasitic worm that infects pets' bodies from infected mosquito bites, is responsible for the disease. The parasites are not natural hosts for humans. Heartworm larvae are often killed before they reach adulthood, so cases in humans are rare. In 2005, a review in the journal Veterinary Parasitology revealed that there were 81 cases of heartworm in humans between 1941 and 2005.

Additional resources

The National Institutes of Health provides information on heart and vascular disease.

The American Heart Association offers tips on how to keep your heart healthy.

This article was last updated by Scott Dutfield, Live Science staff writer.

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