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THE HEART


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PART

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THE HEART

BACKGROUND INFORMATION

ANATOMY

A short introduction to the human heart, with imagery and diagrams to support the information.

Information about the structure, function, shape, size and location of the human heart.

A deconstruction of the human heart and explanations of how each section works.


PART

PART

45 LEONARDO DA VINCI

STATISTICS

A short explanation of Leonardo Da Vinci’s work and some examples of his human heart anatomy drawings.

A number of info graphics supporting some facts and figures about the human heart.

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he human heart is an organ that provides a continuous blood circulation through the cardiac cycle and is one of the most vital organs in the human body. The heart is divided into four main chambers: the two upper chambers are called the left and right atria (singular atrium) and two lower chambers are called the right and left ventricles.

There is a thick wall of muscle separating the right side and the left side of the heart called the septum. Normally with each beat the right ventricle pumps the same amount of blood into the lungs that the left ventricle pumps out into the body. Physicians commonly refer to the right atrium and right ventricle together as the right heart and to the left atrium and left ventricle as the left heart.

THE HEART 4


RIGHT COMMON CAROTID ARTERY RIGHT SUBCLAVIAN ARTERY BRACHIOCEPHALIC TRUNK LEFT PULMONARY ARTERY SUPERIOR VENA CAVA LEFT PULMONARY VEINS LEFT CORONARY ARTERY LEFT ATRIUM

AORTA RIGHT PULMONARY ARTERY MAIN PULMONARY ARTERY RIGHT PULMONART VEINS RIGHT ATRIUM RIGHT CORONARY ARTERY RIGHT VENTRICLE

LEFT VENTRICLE

INFERIOR VENA CAVA APEX

EXTERNAL VIEW OF THE HEART 5


LEFT PULMONARY ARTERY LEFT PULMONARY VEINS MAIN PULMONARY ARTERY LEFT ATRIUM MITRIAL VALVE

LEFT VENTRICLE

AORTA RIGHT PULMONARY ARTERY VENA CAVA RIGHT PULMONARY VEINS PULMONARY VALVE RIGHT ATRIUM

AORTIC VALVE SEPTUM HEART MUSCLE

TRICUSPID VALVE

APEX

RIGHT VENTRICLE

INTERNAL VIEW OF THE HEART 6


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he human heart has a mass of between 250 and 350 grams and is about the size of a fist. It is enclosed in a double-walled protective sac called the pericardium. The double membrane of pericardium consist of the perichordal fluid which nourishes the heart and prevents from shocks. The superficial part of this sac is called the fibrous pericardium. The fibrous perichordal sac is itself lined with the outer layer of the serous pericardium (known as the parietal pericardium). This composite (fibrous-parietal-pericardial) sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood. The inner layer also provides a smooth lubricated sliding surface within which the heart organ can move in response to its own contractions and to movement of adjacent structures such as the diaphragm and lungs.

The outer wall of the human heart is composed of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the (serous) pericardium. The middle layer of the heart is called the myocardium and is composed of muscle which contracts. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves. The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers.

The pathways of blood through the human heart is part of the pulmonary and systemic circuits. These pathways include the tricuspid valve, the mitral valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valves are classified as the atrioventricular (AV) valves. This is because they are found between the atria and ventricles. The aortic and pulmonary semi-lunar valves separate the left and right ventricle from the pulmonary artery and the aorta respectively. These valves are attached to the chordae tendinea (literally the heartstrings), which anchors the valves to the papilla muscles of the heart. The inter atrioventricular septum separates the left atrium and ventricle from the right atrium and ventricle, dividing the heart into two functionally separate and anatomically distinct units.

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lood flows through the heart in one direction, from the atria to the ventricles, and out of the great arteries, or the aorta for example. Blood is prevented from flowing backwards by the tricuspid, bicuspid, aortic, and pulmonary valves. The heart acts as a double pump. The function of the right side of the heart is to collect de-oxygenated blood, in the right atrium, from the body (via superior and inferior vena cavae) and pump it, via the right ventricle, into the lungs (pulmonary circulation) so that carbon dioxide can be dropped off and oxygen picked up (gas exchange). This happens through the passive process of diffusion.

The left side collects oxygenated blood from the lungs into the left atrium. From the left atrium the blood moves to the left ventricle which pumps it out to the body. On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systemic circulation. Atria facilitate circulation primarily by allowing uninterrupted venous flow to the heart, preventing the inertia of interrupted venous flow that would otherwise occur at each ventricular systole.

Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. It is pumped out of the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, blood flows back through the pulmonary vein to the left atrium. It then travels through the mitral valve to the left ventricle, from where it is pumped through the aortic semilunar valve to the aorta and to the rest of the body. The deoxygenated blood finally returns to the heart through the inferior vena cava and superior vena cava, and enters the right atrium where the process began.

FUNCTION 12


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he human heart has a mass of between 250 and 350 grams and is about the size of a fist. It is enclosed in a double-walled protective sac called the pericardium. The double membrane of pericardium consist of the perichordal fluid which nourishes the heart and prevents from shocks. The superficial part of this sac is called the fibrous pericardium. The fibrous perichordal sac is itself lined with the outer layer of the serous pericardium (known as the parietal pericardium). This composite (fibrous-parietal-pericrdial) sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood. The inner layer also provides a smooth lubricated sliding surface within which the heart organ can move in response to its own contractions and to movement of adjacent structures such as the diaphragm and lungs.

The outer wall of the human heart is composed of three layers. The outer layer is called the epicardium, or visceral pericardium since it is also the inner wall of the (serous) pericardium. The middle layer of the heart is called the myocardium and is composed of muscle which contracts. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers heart valves. The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers. The pathways of blood through the human heart is part of the pulmonary and systemic circuits.

These pathways include the tricuspid valve, the mitral valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valves are classified as the atrioventricular (AV) valves. This is because they are found between the atria and ventricles. The aortic and pulmonary semi-lunar valves separate the left and right ventricle from the pulmonary artery and the aorta respectively. These valves are attached to the chordae tendinea (literally the heartstrings), which anchors the valves to the papilla muscles of the heart. The inter atrioventricular septum separates the left atrium and ventricle from the right atrium and ventricle, dividing the heart into two functionally separate and anatomically distinct units.

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CORONARY ARTERIES The heart is composed primarily of cardiac muscle tissue that continuously contracts and relaxes, it must have a constant supply of oxygen and nutrients. The coronary arteries are the network of blood vessels that carry oxygen- and nutrient-rich blood to the cardiac muscle tissue. The blood leaving the left ventricle exits through the aorta, the body’s main artery. Two coronary arteries, referred to as the “left” and “right” coronary arteries, emerge from the beginning of the aorta, near the top of the heart. The initial segment of the left coronary artery is called the left main coronary. This blood vessel is approximately the width of a soda straw and is less than an inch long. It branches into two slightly smaller arteries: the left anterior descending coronary artery and the left circumflex coronary artery. The left anterior descending coronary artery is embedded in the surface of the front side of the heart. The left circumflex coronary artery circles around the left side of the heart and is embedded in the surface of the back of the heart.

SUPERIOR VENA CAVA Just like branches on a tree, the coronary arteries branch into progressively smaller vessels. The larger vessels travel along the surface of the heart; however, the smaller branches penetrate the heart muscle. The smallest branches, called capillaries, are so narrow that the red blood cells must travel in single file. In the capillaries, the red blood cells provide oxygen and nutrients to the cardiac muscle tissue and bond with carbon dioxide and other metabolic waste products, taking them away from the heart for disposal through the lungs, kidneys and liver. When cholesterol plaque accumulates to the point of blocking the flow of blood through a coronary artery, the cardiac muscle tissue fed by the coronary artery beyond the point of the blockage is deprived of oxygen and nutrients. This area of cardiac muscle tissue ceases to function properly. The condition when a coronary artery becomes blocked causing damage to the cardiac muscle tissue it serves is called a myocardial infarction or heart attack.

The superior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava, which empties into the right atrium of the heart.

INFERIOR VENA CAVA The inferior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart.

AORTA The aorta is the largest single blood vessel in the body. It is approximately the diameter of your thumb. This vessel carries oxygen-rich blood from the left ventricle to the various parts of the body.

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PULMONARY ARTERY

RIGHT VENTRICLE

LEFT VENTRICLE

The pulmonary artery is the vessel transporting de-oxygenated blood from the right ventricle to the lungs. A common misconception is that all arteries carry oxygen-rich blood. It is more appropriate to classify arteries as vessels carrying blood away from the heart.

The right ventricle receives de-oxygenated blood as the right atrium contracts. The pulmonary valve leading into the pulmonary artery is closed, allowing the ventricle to fill with blood. Once the ventricles are full, they contract. As the right ventricle contracts, the tricuspid valve closes and the pulmonary valve opens. The closure of the tricuspid valve prevents blood from backing into the right atrium and the opening of the pulmonary valve allows the blood to flow into the pulmonary artery toward the lungs.

The left ventricle receives oxygenated blood as the left atrium contracts. The blood passes through the mitral valve into the left ventricle. The aortic valve leading into the aorta is closed, allowing the ventricle to fill with blood. Once the ventricles are full, they contract. As the left ventricle contracts, the mitral valve closes and the aortic valve opens. The closure of the mitral valve prevents blood from backing into the left atrium and the opening of the aortic valve allows the blood to flow into the aorta and flow throughout the body.

PAPILLARY MUSCLES

LEFT ATRIUM

The papillary muscles attach to the lower portion of the interior wall of the ventricles. They connect to the chordae tendineae, which attach to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. The contraction of the papillary muscles closes these valves. When the papillary muscles relax, the valves open.

The left atrium receives oxygenated blood from the lungs through the pulmonary vein. As the contraction triggered by the sino-atrial node progresses through the atria, the blood passes through the mitral valve into the left ventricle.

PULMONARY VEIN The pulmonary vein is the vessel transporting oxygen-rich blood from the lungs to the left atrium. A common misconception is that all veins carry de-oxygenated blood. It is more appropriate to classify veins as vessels carrying blood to the heart.

RIGHT ATRIUM The right atrium receives de-oxygenated blood from the body through the superior vena cava (head and upper body) and inferior vena cava (legs and lower torso). The sino-atrial node sends an impulse that causes the cardiac muscle tissue of the atrium to contract in a coordinated, wave-like manner. The tricuspid valve, which separates the right atrium from the right ventricle, opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle.

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CHORDAE TENDINEAE

MITRAL VALVE

AORTIC VALVE

The chordae tendineae are tendons linking the papillary muscles to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. As the papillary muscles contract and relax, the chordae tendineae transmit the resulting increase and decrease in tension to the respective valves, causing them to open and close. The chordae tendineae are string-like in appearance and are sometimes referred to as “heart strings.�

The mitral valve separates the left atrium from the left ventricle. It opens to allow the oxygenated blood collected in the left atrium to flow into the left ventricle. It closes as the left ventricle contracts, preventing blood from returning to the left atrium; thereby, forcing it to exit through the aortic valve into the aorta.

The aortic valve separates the left ventricle from the aorta. As the ventricles contract, it opens to allow the oxygenated blood collected in the left ventricle to flow throughout the body. It closes as the ventricles relax, preventing blood from returning to the heart.

TRICUSPID VALVE The tricuspid valve separates the right atrium from the right ventricle. It opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle. It closes as the right ventricle contracts, preventing blood from returning to the right atrium; thereby, forcing it to exit through the pulmonary valve into the pulmonary artery.

PULMONARY VALVE The pulmonary valve separates the right ventricle from the pulmonary artery. As the ventricles contract, it opens to allow the de-oxygenated blood collected in the right ventricle to flow to the lungs. It closes as the ventricles relax, preventing blood from returning to the heart.

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LEONARDO DA VINCI 20


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eonardo’s last extensive investigation which has survived is a series of drawings of the heart and rib cage, uniformly executed in pale ink on coarse blue paper. RL 19077 bears the date 9th January 1513, but the series seems to have been compiled over a considerable period of time, maybe during the couple of years before Leonardo left Milan for Rome in September 1513. Precise dating is impossible. Only now, towards the end of Leonardo’s anatomical career, does the text begin to vie with illustration for primacy. The present sheet is the most heavily Illustrated of the series, and several sheets contain solid blocks of notes with only marginal sketches. Also, the relationship between word and image has changed: drawing illustrates text, and text explains drawing, with an intimacy quite different from the patchworks of cats.

The three-cusped valves of the heart were seen by Leonardo as a perfect example of mathematical necessity in the workings of nature. As blood was forced through the valve, eddies in the sinuses curved back into the cusps of the valve. When the flow ceased, these eddies opened the cusps against one another to form a perfect seal, preventing reflux. Two cusps would not allow a sufficient aperture for flux of the blood; four cusps would be too weak in closure. Three was the optimum number, and that is what nature had provided.

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ARTERIES VEINS

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he human heart is made up of two different kinds of blood vessels. Blood vessels are hollow tubes that carry blood all over the human body. The human body has three kinds of vessels: arteries, veins and capillaries. In the human heart there are arteries and veins. Arteries carry blood away from the heart and veins carry blood towards the heart. Capillaries connect the arteries to the vein, throughout the body.

The deeper shade of red on the heart diagram is representing arteries and the lighter shade of red is representing the veins in the human heart.

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his info graphic shows how many times your heart beats a day, against how many gallons of blood surge through your body, against how many miles of blood vessels that feed your organs and tissues. It is colour coded to show the comparison.

EVERY DAY, YOUR HEART BEATS ABOUT 100,000 TIMES

SENDING 2,000 GALLONS OF BLOOD SURGING THROUGH YOUR BODY

THE HEART KEEPS BLOOD FLOWING THROUGH THE 60,000 MILES OF BLOOD VESSELS THAT FEED YOUR ORGANS AND TISSUES

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f you would like more information on the human heart you can listen to the BBC Radio 4 ‘In Our Time’ episode ‘The Heart’. Where Melvyn Bragg and guests discuss the human heart in more detail. If you own a smart phone, simply scan the QR code on the page 28 and it will take you directly there.

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Images, text and diagrams accumulated by

LAUREN MURPHY


The Heart