Anatomy and Function of the Heart

• The heart is a hollow muscular organ protected by the pericardium.
• The pericardium minimizes friction during heart contraction.
• The heart wall consists of cardiac muscle, divided into right and left halves, each with an atrium and ventricle.

Atria and Ventricles

• The right atrium and right ventricle are separated by the tricuspid valve.
• The left atrium and left ventricle are separated by the bicuspid (mitral) valve.
• The tricuspid and bicuspid valves are known as atrioventricular (A-V) valves.
• Papillary muscles in the ventricles attach to the A-V valves via chordae tendineae.
• Chordae tendineae prevent A-V valves from everting into the atria during ventricular contraction.
• The aorta originates from the left ventricle, guarded by the aortic valve.
• The pulmonary artery originates from the right ventricle, guarded by the pulmonary valve.

Heart Valves

• Heart valves ensure unidirectional blood flow.
• The inner surface of the myocardium is lined with the endocardium.
• Endocardium also lines cardiac valves and the entire vascular system.
• Atrial myocardium is thinner than ventricular myocardium.
• The left ventricular wall is 3 times thicker than the right (15 mm vs. 5 mm).
• Left ventricular contraction aids the right ventricle by generating pressure.

Coronary Arteries

• Coronary arteries supply blood to the myocardium, originating from the aorta's first part.
• Coronary arteries transition into small arteries, arterioles, capillaries, venules and veins.

High and Low Pressure Systems

• Capillaries are divided into high-pressure (arterial) and low-pressure (venous) components.
• The functional capillary pressure marking this division is 17 mmHg.

Components of the Low-Pressure System

• Systemic veins are part of the low-pressure system.
• Pulmonary vessels are part of the low-pressure system.
• Right and left atria.
• Right and left ventricles during diastole.
• The low-pressure system contains more blood volume at lower pressure.

Components of the High-Pressure System

• Systemic arterial system (aorta, arteries, arterioles).
• Right and left ventricles during systole.
• Arterial side of capillaries.
• The high-pressure system contains less blood volume at higher pressure.

Atrial Function

• Atria receive and store venous return during ventricular systole.
• Atria passively pass blood to ventricles during ventricular diastole.
• Atrial systole increases ventricular filling by 20%.
• Loss of atrial function is not fatal.
• Atrial walls contain stretch receptors, which monitor intra-atrial pressure and initiate cardiovascular reflexes.
• Atrial cells monitor changes in blood volume and release Atrial Natriuretic Peptide.
• Atrial Natriuretic Peptide promotes Na+ and H2O excretion by the kidneys.

Ventricular Function

• Ventricles pump blood to the peripheral circulation.
• Loss of ventricular function is fatal.

Contractile Cells

• Contractile cells, comprising 99% of cardiac muscle, form atrial and ventricular walls.
• Contractile cells are responsible for pumping blood.

Autorhythmic Cells

• Autorhythmic cells, comprising 1% of cardiac muscle, form the heart's conducting system.
• Autorhythmic cells are specialized for initiating and conducting impulses.

Types of Circulation

• Systemic (greater) circulation
• Pulmonary (lesser) circulation
• Special circulation