The heart is a muscular organ around the dimension of a closed fist that functions as the body circulatory pump. It takes in deoxygenated blood through the veins and also delivers it to the lungs because that oxygenation before pumping it into the various arteries (which administer oxygen and nutrients to body tissues by carrying the blood throughout the body). The heart is located in the thoracic cavity medial come the lungs and also posterior to the sternum.

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continued From Above... pulmonary arteries and veins, and the vena cava. The inferior reminder of the heart, known as the apex, rests simply superior come the diaphragm. The basic of the love is located along the body’s midline with the apex pointing towards the left side. Since the love points come the left, about 2/3 that the heart’s fixed is found on the left side of the body and also the other 1/3 is on the right.

Anatomy of the Heart


The heart sit within a fluid-filled cavity dubbed the pericardial cavity. The walls and lining of the pericardial cavity room a special membrane known as the pericardium. Pericardium is a type of serous membrane that produces serous fluid to lubricate the heart and also prevent friction in between the ever beating heart and also its surrounding organs. Besides lubrication, the pericardium serves to host the love in position and maintain a hollow space for the heart to expand into as soon as it is full. The pericardium has actually 2 layers—a visceral layer the covers the external of the heart and also a parietal great that creates a sac around the external of the pericardial cavity.

Structure that the love Wall

The heart wall surface is make of 3 layers: epicardium, myocardium and also endocardium.

Epicardium. The epicardium is the outermost great of the heart wall surface and is just an additional name for the visceral layer of the pericardium. Thus, the epicardium is a slim layer of serous membrane that helps to lubricate and also protect the outside of the heart. Listed below the epicardium is the second, thicker class of the love wall: the myocardium. Endocardium. Endocardium is the simple squamous endothelium layer the lines the inside of the heart. The endocardium is very smooth and is responsible for keeping blood from difficult to the inside of the heart and also forming perhaps deadly blood clots.

The thickness of the heart wall surface varies in different parts that the heart. The atria of the heart have actually a very thin myocardium because they execute not have to pump blood an extremely far—only to the surrounding ventricles. The ventricles, top top the other hand, have a really thick myocardium to pump blood come the lungs or transparent the entire body. The appropriate side that the heart has less myocardium in its walls than the left side because the left side has to pump blood with the whole body when the appropriate side only has to pump come the lungs.

Chambers of the Heart

The heart consists of 4 chambers: the right atrium, left atrium, right ventricle, and left ventricle. The atria are smaller sized than the ventricles and also have thinner, much less muscular walls than the ventricles. The atria act together receiving chambers for blood, for this reason they are associated to the veins that bring blood come the heart. The ventricles room the larger, stronger pumping chambers that send blood out of the heart. The ventricles are associated to the arteries that carry blood far from the heart.

The chambers ~ above the ideal side that the heart room smaller and also have less myocardium in your heart wall when contrasted to the left next of the heart. This distinction in size in between the sides of the heart is related to their functions and also the dimension of the 2 circulatory loops. The right side that the heart maintains pulmonary circulation to the adjacent lungs if the left next of the heart pumps blood all the way to the extremities of the body in the systemic circulatory loop.

Valves the the Heart

The heart features by pump blood both come the lungs and to the solution of the body. To protect against blood from flow backwards or “regurgitating” earlier into the heart, a mechanism of one-way valves are existing in the heart. The love valves can be broken down into two types: atrioventricular and also semilunar valves.

Conduction system of the Heart

The love is able come both collection its very own rhythm and to conduct the signals necessary to maintain and also coordinate this rhythm throughout its structures. Around 1% of the cardiac muscle cell in the heart room responsible for forming the conduction mechanism that sets the speed for the rest of the cardiac muscle cells.

The conduction system starts with the pacemaker the the heart—a little bundle the cells known as the sinoatrial (SA) node. The SA node is located in the wall surface of the ideal atrium inferior to the superior vena cava. The SA node is responsible for setup the pace of the heart as a whole and directly signal the atria to contract. The signal native the SA node is choose up by one more mass the conductive tissue well-known as the atrioventricular (AV) node.

The AV node is located in the appropriate atrium in the inferior section of the interatrial septum. The AV node choose up the signal sent out by the SA node and also transmits it with the atrioventricular (AV) bundle. The AV bundle is a strand the conductive organization that runs with the interatrial septum and also into the interventricular septum. The AV bundle splits into left and also right branches in the interventricular septum and continues running v the septum till they reach the apex of the heart. Branching turn off from the left and also right bundle branches are numerous Purkinje fibers that carry the signal to the walls of the ventricles, stimulating the cardiac muscle cells to contract in a combination manner to efficiently pump blood the end of the heart.

Physiology of the Heart

Coronary Systole and also Diastole

At any given time the chambers that the love may discovered in among two states:

Systole. During systole, cardiac muscle tissue is contracting to push blood the end of the chamber. Diastole. During diastole, the cardiac muscle cells relax to enable the room to fill through blood. Blood pressure rises in the significant arteries during ventricular systole and also decreases throughout ventricular diastole. This leads to the 2 numbers associated with blood pressure—systolic blood pressure is the greater number and also diastolic blood pressure is the reduced number. Because that example, a blood push of 120/80 explains the systolic press (120) and the diastolic pressure (80).

The Cardiac Cycle

The cardiac cycle includes every one of the occasions that take place throughout one heartbeat. There are 3 phases to the cardiac cycle: atrial systole, ventricular systole, and also relaxation.

Atrial systole: throughout the atrial systole step of the cardiac cycle, the atria contract and also push blood right into the ventricles. Come facilitate this filling, the AV valves remain open and also the semilunar valves stay closed to keep arterial blood native re-entering the heart. The atria are much smaller 보다 the ventricles, for this reason they just fill around 25% of the ventricles throughout this phase. The ventricles stay in diastole during this phase. Ventricular systole: during ventricular systole, the ventricles contract to press blood right into the aorta and pulmonary trunk. The press of the ventricles pressures the semilunar valves to open and also the AV valves to close. This setup of valves enables for blood flow from the ventricles into the arteries. The cardiac muscles of the atria repolarize and enter the state of diastole throughout this phase. Relaxation phase: during the be safe phase, all 4 chambers that the heart space in diastole together blood pours into the heart from the veins. The ventricles to fill to around 75% capacity throughout this phase and also will be completely filled only after the atria get in systole. The cardiac muscle cells of the ventricles repolarize during this phase to prepare because that the next round of depolarization and also contraction. Throughout this phase, the AV valves open to allow blood to flow freely into the ventricles while the semilunar valves close to protect against the regurgitation of blood from the good arteries right into the ventricles.

Blood flow through the Heart

Deoxygenated blood returning from the body an initial enters the heart from the superior and also inferior vena cava. The blood beginning the best atrium and also is pumped through the tricuspid valve into the appropriate ventricle. From the best ventricle, the blood is pumped v the pulmonary semilunar valve into the pulmonary trunk.

The pulmonary tribe carries blood come the lungs where it release carbon dioxide and absorbs oxygen. The blood in the lung returns come the heart through the pulmonary veins. Indigenous the pulmonary veins, blood beginning the love again in the left atrium.

The left atrium contract to pump blood through the bicuspid (mitral) valve right into the left ventricle. The left ventricle pumps blood through the aortic semilunar valve into the aorta. Native the aorta, blood enters right into systemic circulation throughout the body tissues till it return to the love via the vena cava and also the cycle repeats.

The Electrocardiogram

The electrocardiogram (also recognized as an EKG or ECG) is a non-invasive device that measures and also monitors the electrical activity of the heart through the skin. The EKG produces a distinctive waveform in an answer to the electrical changes taking location within the heart.

The very first part of the wave, referred to as the p wave, is a little increase in voltage of around 0.1 mV that coincides to the depolarization of the atria throughout atrial systole. The next component of the EKG tide is the QRS facility which functions a tiny drop in voltage (Q) a huge voltage peak (R) and also another little drop in voltage (S). The QRS complex corresponds come the depolarization the the ventricles throughout ventricular systole. The atria also repolarize during the QRS complex, yet have almost no impact on the EKG due to the fact that they room so much smaller 보다 the ventricles.

The final part of the EKG tide is the T wave, a tiny peak that follows the QRS complex. The T tide represents the ventricular repolarization throughout the relaxation step of the cardiac cycle. Sports in the waveform and also distance between the waves of the EKG can be provided clinically come diagnose the effects of love attacks, congenital heart problems, and electrolyte imbalances.

Heart Sounds

The sound of a regular heartbeat are recognized as “lubb” and “dupp” and also are resulted in by blood pushing on the valves the the heart. The “lubb” sound comes very first in the heartbeat and also is the longer of the two heart sounds. The “lubb” sound is created by the closing of the AV valves in ~ the start of ventricular systole. The shorter, sharper “dupp” sound is an in similar way caused through the closeup of the door of the semilunar valves in ~ the end of ventricular systole. During a normal heartbeat, these sounds repeat in a regular pattern the lubb-dupp-pause. Any added sounds such as liquid rushing or gurgling suggest a structure problem in the heart. The many likely reasons of this extraneous sounds room defects in the atrial or ventricular septum or leakage in the valves.

Cardiac Output

Cardiac calculation (CO) is the volume the blood gift pumped through the heart in one minute. The equation used to uncover cardiac calculation is: CO = stroke Volume x love Rate

Stroke volume is the lot of blood pumped into the aorta during each ventricular systole, usually measured in milliliters. Heart rate is the number of heartbeats per minute. The mean heart have the right to push about 5 come 5.5 liters every minute in ~ rest.

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Heart wellness Problems

Heart condition is very common, disrupting the normal duty of this crucial organ and also often resulting in death. Visit ours Diseases and Conditions section to learn an ext about typical cardiovascular diseases and how we can prevent them. For information about your an individual hereditary risks of a range of conditions involving the heart (such as those emerging from hemochromatosis or G6PDD, to surname two really common hereditary disorders), learn much more about DNA health testing.