Heart

Arteries

Blood vessels that transport blood away from the heart, typically high in oxygen (except pulmonary arteries).

Veins

Blood vessels that transport blood toward the heart, typically low in oxygen (except pulmonary veins).

Capillaries

Sites of exchange between blood and systemic cells or alveoli of the lungs.

Pulmonary circulation

Transports deoxygenated blood from the right side of the heart to the lungs and back to left side of the heart.

Systemic circulation

Transports oxygenated blood from the left side of the heart to systemic capillaries and back to the right side.

Sinoatrial (SA) node

The natural pacemaker of the heart, located in the right atrium.

Atrioventricular (AV) node

Slows conduction of impulses from atria to ventricles, part of the heart's conduction system.

Intercalated discs

Structures in cardiac muscle that contain desmosomes and gap junctions to allow synchronized contractions.

Fibrous skeleton

Dense connective tissue structure that provides support and acts as an electrical insulator between atria and ventricles.

Auricle

A wrinkled extension of an atrium that increases its volume.

Blood flow of the heart

right side of the heart → lungs → left side of heart → systemic capillaries of body → back to right side of heart

Pericardium

The fibrous sac surrounding the heart, providing protection and anchoring it within the thoracic cavity.

Fibrous pericardium

The tough outer layer of the pericardium that provides stability and protection to the heart.

Serous pericardium

The inner layer of the pericardium, consisting of two layers: parietal and visceral, which helps reduce friction between the heart and surrounding structures.

Pericardial cavity

The space between the parietal and visceral layers of the serous pericardium, filled with pericardial fluid that lubricates the heart.

Heart wall structure

The three layers of the heart wall: epicardium (outer), myocardium (middle, muscular layer), and endocardium (inner lining).

Four hollow chambers of the heart

The heart consists of two smaller atria (right and left) and two larger ventricles (right and left) that facilitate blood flow and circulation.

Heart Valves

Valves in the heart prevent backflow of blood, ensuring unidirectional flow throughout the heart.

Dual Pump Mechanism

The heart functions as two side-by-side pumps, one directing blood to the lungs and the other to body tissues, working at the same rate.

Blood Pressure Regulation

The heart establishes and maintains blood pressure through cycles of contraction and relaxation of the heart wall.

Blood Flow Through Cardiac Cycle

Blood flows through the heart in a sequence that follows the phases of the cardiac cycle.

Blood Flows from High Pressure to Low Pressure

Blood always moves from areas of higher pressure (ventricles) to areas of lower pressure (atria and vessels).

Valves Keep Blood Flowing in One Direction

Heart valves prevent backflow of blood, ensuring unidirectional flow throughout the cardiac cycle.

Blood Flows from Veins into Atria Under Low Pressure

Blood returning from the body flows into the atria under low pressure, allowing for filling during relaxation.

70% Ventricular Filling Occurs Passively

Most ventricular filling (70%) occurs passively when both atria and ventricles are relaxed.

Ventricular Contraction (Systole) Increases Pressure on Blood

During ventricular systole, pressure rises, closing the AV valves and opening semilunar valves to eject blood.

Atrial relaxation and ventricular filling

Phase in the cardiac cycle when the atria relax and blood flows into the ventricles, preparing them for contraction.

Atrial contraction and ventricular filling

Phase in the cardiac cycle characterized by atrial contraction forcing additional blood into the ventricles just before ventricular systole.

Isovolumic contraction

Phase when ventricles contract with no volume change as all heart valves are closed, increasing pressure without ejecting blood.

Ventricular ejection

Phase in the cardiac cycle when the ventricles contract and blood is pushed into the pulmonary artery and aorta.

Isovolumic relaxation

Phase when ventricles relax after ejection, with closed valves preventing blood backflow and no change in volume until pressure falls.

Conduction System of the Heart

The system that generates and maintains the electrical impulses that initiate and regulate heartbeats.

Sympathetic Innervation of the Heart

The part of the autonomic nervous system that increases heart rate and force of contraction during stress or physical activity.

Parasympathetic Innervation of the Heart

The part of the autonomic nervous system that decreases heart rate and