Anatomy of the Heart

• The heart is a muscular organ responsible for pumping blood throughout the body via the circulatory system, providing oxygen and nutrients to tissues and removing carbon dioxide and other wastes.
• It is located in the mediastinum, the central compartment of the thoracic cavity.
• The heart consists of four chambers: two atria (right and left) and two ventricles (right and left).
• The atria receive blood returning to the heart, while the ventricles pump blood away from the heart.

Structure of the Heart

• The heart wall is composed of three layers: the epicardium, myocardium, and endocardium.
• The epicardium is the outermost layer, also known as the visceral pericardium.
• The myocardium is the thick middle layer composed of cardiac muscle tissue, responsible for the heart's pumping action.
• The endocardium is the innermost layer lining the heart chambers and covering the valves.
• The heart is surrounded by a double-layered sac called the pericardium, which protects and lubricates the heart.
• The pericardium consists of two layers: the fibrous pericardium and the serous pericardium.
• The serous pericardium is further divided into the parietal and visceral layers, with the pericardial cavity in between containing pericardial fluid to reduce friction.

Chambers and Valves

• The right atrium receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus.
• The left atrium receives oxygenated blood from the pulmonary veins.
• The right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery.
• The left ventricle pumps oxygenated blood to the body through the aorta.
• Valves ensure unidirectional blood flow through the heart.
• The atrioventricular (AV) valves are located between the atria and ventricles: the tricuspid valve (right side) and the mitral valve (left side).
• The semilunar valves are located between the ventricles and the great arteries: the pulmonary valve (right side) and the aortic valve (left side).
• Chordae tendineae and papillary muscles prevent the AV valves from inverting during ventricular contraction.

Blood Flow through the Heart

• Deoxygenated blood enters the right atrium through the superior and inferior vena cavae.
• Blood flows from the right atrium to the right ventricle through the tricuspid valve.
• The right ventricle pumps blood through the pulmonary valve into the pulmonary artery, which carries it to the lungs.
• In the lungs, blood releases carbon dioxide and picks up oxygen.
• Oxygenated blood returns to the left atrium through the pulmonary veins.
• Blood flows from the left atrium to the left ventricle through the mitral valve.
• The left ventricle pumps blood through the aortic valve into the aorta, which distributes it to the body.

Cardiac Cycle

• The cardiac cycle consists of two phases: systole (contraction) and diastole (relaxation).
• During systole, the ventricles contract, pumping blood into the pulmonary artery and aorta.
• During diastole, the ventricles relax and fill with blood from the atria.
• Atrial systole occurs when the atria contract, pushing additional blood into the ventricles just before ventricular systole.
• The "lub" sound (S1) is caused by the closing of the AV valves at the beginning of ventricular systole.
• The "dub" sound (S2) is caused by the closing of the semilunar valves at the beginning of ventricular diastole.

Conduction System of the Heart

• The heart has an intrinsic conduction system that controls the heart rate and coordinates the contraction of the atria and ventricles.
• The sinoatrial (SA) node, located in the right atrium, is the heart's primary pacemaker, initiating electrical impulses.
• The atrioventricular (AV) node, located between the atria and ventricles, receives impulses from the SA node and delays them briefly.
• The bundle of His (atrioventricular bundle) conducts impulses from the AV node to the ventricles.
• The bundle branches split the signal and carry impulses through the interventricular septum.
• Purkinje fibers distribute impulses throughout the ventricular myocardium, causing ventricular contraction.
• An electrocardiogram (ECG or EKG) records the electrical activity of the heart, showing P waves (atrial depolarization), QRS complex (ventricular depolarization), and T waves (ventricular repolarization).

Regulation of Heart Rate

• The heart rate is regulated by the autonomic nervous system, hormones, and other factors.
• The sympathetic nervous system increases heart rate and contractility through the release of norepinephrine.
• The parasympathetic nervous system decreases heart rate through the release of acetylcholine.
• Hormones such as epinephrine and thyroid hormones can increase heart rate.
• Baroreceptors and chemoreceptors respond to changes in blood pressure and blood chemistry, influencing heart rate.
• Factors such as age, fitness level, and body temperature can also affect heart rate.

Coronary Circulation

• The heart receives its own blood supply through the coronary arteries.
• The left coronary artery branches into the left anterior descending (LAD) artery and the circumflex artery.
• The right coronary artery supplies the right atrium, right ventricle, and part of the left ventricle.
• Blockage of the coronary arteries can lead to myocardial ischemia or infarction (heart attack).
• Coronary artery disease (CAD) is a common condition characterized by the buildup of plaque in the coronary arteries.

Common Heart Conditions

• Arrhythmias are abnormalities in the heart's rhythm, such as atrial fibrillation, ventricular tachycardia, and bradycardia.
• Heart failure occurs when the heart is unable to pump enough blood to meet the body's needs.
• Valvular heart disease involves problems with the heart valves, such as stenosis (narrowing) or regurgitation (leakage).
• Congenital heart defects are structural abnormalities present at birth.
• Cardiomyopathy refers to diseases of the heart muscle.

Diagnostic Tests

• Electrocardiogram (ECG) records the electrical activity of the heart.
• Echocardiogram uses ultrasound to visualize the heart's structure and function.
• Stress test evaluates the heart's response to exercise or medication.
• Cardiac catheterization involves inserting a catheter into a blood vessel to assess heart function and coronary arteries.
• Blood tests can measure cardiac enzymes and other markers of heart health.

Maintaining Heart Health

• Regular exercise helps strengthen the heart and improve cardiovascular health.
• A healthy diet low in saturated fat, cholesterol, and sodium can reduce the risk of heart disease.
• Maintaining a healthy weight can reduce strain on the heart.
• Avoiding smoking and limiting alcohol consumption can improve heart health.
• Managing stress through relaxation techniques and other strategies can benefit the heart.
• Regular check-ups with a healthcare provider can help detect and manage heart problems early.

The heart is a muscular organ that pumps blood throughout the body. It consists of four chambers: two atria and two ventricles. The heart wall has three layers: the epicardium, myocardium, and endocardium.