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The heart is the organ that supplies blood and oxygen to all parts of the body. It is about the size of a clenched fist, weighs about 10.5 ounces and is shaped like a cone. The heart is located in the chest cavity just posterior to the breastbone, between the lungs and superior to the diaphragm. The heart is surrounded by a fluid filled sac called the pericardium. Blood is pumped away from the heart through arteries and returns to the heart through veins. The major artery of the body is the aorta and the major veins of the body are the vena cava

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The pericardium is the fluid filled sac that surrounds the heart and the proximal ends of the aorta, vena cava and the pulmonary artery

Function: Keeps the heart contained in the chest

cavity. Prevents the heart from overexpanding

when blood volume increases. Limits heart motion.

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Blood vessels are intricate networks of tubes that transport blood throughout the entire body.

Types of vessels: Arteries Veins Capillaries Sinusoids

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What is the epicardium? The epicardium is the outer layer of

the wall of the heart. It is composed of connective tissue covered by epithelium. The epicardium is also known as the visceral pericardium.

Function: Provides an outer protective layer for

the heart

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What is the myocardium? Myocardium is the muscular middle layer

of the wall of the heart. It is composed of spontaneously contracting cardiac muscle fibers which allow the heart to contract.

Function: Stimulates heart contractions to pump

blood from the ventricles and relaxes the heart to allow the artria to receive blood.

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What is the endocardium? The endocardium is the inner layer of

the heart. It consists of epithelial tissue and connective tissue.

Function: Lines the inner cavities of the heart,

covers heart valves and is continuous with the inner lining of blood vessels.

Purkinje fibers are located in the endocardium. They participate in the contraction of the heart muscle.

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What are atria? The heart is divided into four chambers

that are connected by valves. The upper two chambers of the heart are called the left atrium and the right atrium.

Function: Right Atrium: Receives blood returning

to the heart from the superior and inferior vena cava.

Left Atrium: Receives blood returning to the heart from the pulmonary veins

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What are ventricles? The heart is divided into four chambers

that are connected by valves. The lower two chambers of the heart are called the left ventricle and the right ventricle.

Function: Right Ventricle: Receives blood from the

right atrium and pumps it to the pulmonary artery.

Left Ventricle: Receives blood from the left atrium and pumps it to the aorta.

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Valves are flap-like structures that allow blood to flow in one direction. The heart has two kinds of valves, atrioventricular and semilunar valves.

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The atrioventricular valves are thin structures that are composed of endocardium and connective tissue. They are located between the atria and the ventricles

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What is the mitral valve? Valves are flap-like structures that

allow blood to flow in one direction. The mitral valve is located between the left atrium and the left ventricle.

Function: Prevents the back flow of blood as it

is pumped from the left atrium to the left ventricle.

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What is the tricuspid valve? Valves are flap-like structures that

allow blood to flow in one direction. The tricuspid valve is located between the right atrium and the right ventricle.

Function: Prevents the back flow of blood as it is

pumped from the right atrium to the right ventricle.

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The semilunar valves are flaps of endocardium and connective tissue reinforced by fibers which prevent the valves from turning inside out. They are shaped like a half moon, hence the name semilunar (semi-, -lunar). The semilunar valves are located between the aorta and the left ventricle and between the pulmonary artery and the right ventricle.

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What is the aortic valve? Valves are flap-like structures that

allow blood to flow in one direction. The aortic valve is located between the left ventricle and the aorta.

Function: Prevents the back flow of blood as it

is pumped from the left ventricle to the aorta.

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What is the pulmonary valve? Valves are flap-like structures that

allow blood to flow in one direction. The pulmonary valve is located between the right ventricle and the pulmonary artery.

Function: Prevents the back flow of blood as it is

pumped from the right ventricle to the pulmonary artery

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Cardiac Conduction system

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Sinoatrial Node

What is the sinoatrial node? The sinoatrial (SA) node is a section of

nodal tissue that is located in the upper wall of the right atrium. The SA node is also referred to as the pacemaker of the heart.

Function: Sets the rate of contraction for the heart. Spontaneously contracts and generates

nerve impulses that travel throughout the heart wall causing both atria to contract.

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Atrioventricular BundleWhat is the atrioventricular bundle? The atrioventricular bundle is a

bundle of fibers that are located within the septum of the heart.

Function: Carries cardiac impulses down the

septum to the ventricles via the Purkinje fibers

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Atrioventricular Node

What is the atrioventricular node? The atrioventricular (AV) node is a section

of nodal tissue that lies on the right side of the partition that divides the atria, near the bottom of the right atrium.

Function: Delays cardiac impulses from the

sinoatrial node to allow the atria to contract and empty their contents first.

Relays cardiac impulses to the atrioventricular bundle

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Purkinje Fibers

What are Purkinje fibers? Purkinje fibers are fiber branches

that extend from the atrioventricular bundle.

Function: Relays cardiac impulses to the

ventricular cells causing the ventricles to contract

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Cardiac Cycle

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The cardiac cycle is the sequence of events that occur when the heart beats. There are two phases of this cycle: Diastole - Ventricles are relaxed. Systole - Ventricles contract.

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Cardiac CycleImage courtesy of MedValet

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Diastole Phase

The cardiac cycle is the sequence of events that occur when the heart beats. There are two phases of this cycle:

Diastole - Ventricles are relaxed. Systole - Ventricles contract

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Cardiac Cycle Diastole Phase

Early Diastole

Ventricles relax. Semilunar valves close.

Atrioventricular valves open. Ventricles fill with blood.

Mid Diastole

Atria and Ventricles are relaxed. Semilunar valves are closed.

Atrioventricular valves are open. Ventricles continue to fill with

blood.

Late Diastole

SA node contracts. Atria contract.

Ventricles fill with more blood. Contraction reaches AV node.

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Systole Phase

The cardiac cycle is the sequence of events that occur when the heart beats. There are two phases of this cycle:

Diastole - Ventricles are relaxed. Systole - Ventricles contract

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Systole

Contraction passes from AV node to Purkinje fibers and ventricular cells.

Ventricles contract. Atrioventricular valves close.

Semilunar valves open. Blood is pumped from the ventricles

to the arteries.

Cardiac Cycle Systole Phase

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Blood vessels

ArteriesCapillariesVeins

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What is the aorta?

Arteries are vessels that carry blood away from the heart. The aorta is the largest artery in the body. It arises from the left ventricle of the heart, forms an arch, then extends down to the abdomen where it branches off into two smaller arteries.

Function: Carries and distributes oxygen rich blood to all

arteries. Most major arteries branch off from the aorta, with the exception of the main pulmonary artery.

Branches: (1) Ascending Aorta - Extends from the left

ventricle of the heart.

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Coronary Arteries

The coronary arteries are the first blood vessels that branch off from the ascending aorta.

Function: Carry oxygenated and nutrient filled

blood to the heart muscle

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Main Pulmonary Artery

Function: Carries de-oxygenated blood from

the right ventricle to the lungs

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Pulmonary Veins

Function: Brings oxygenated blood from the

lungs to the left atrium

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Vena Cavae

Function: Superior Vena Cava: Brings de-

oxygenated blood from the head, neck, arm and chest regions of the body to the right atrium.

Inferior Vena Cava: Brings de-oxygenated blood from the lower body regions to the right atrium.