The heart's four chambers work together to pump blood through the body. The right side handles deoxygenated blood, while the left side manages oxygenated blood. This intricate system ensures efficient circulation and oxygen delivery to tissues.

Four valves in the heart maintain unidirectional blood flow, preventing backflow and mixing of oxygenated and deoxygenated blood. These valves open and close in response to pressure changes, creating the familiar "lub-dub" sound of a heartbeat.

Heart Chambers and Location

Anatomy of the Four Heart Chambers

• The heart consists of four chambers: the right atrium, right ventricle, left atrium, and left ventricle
• The atria are located superior to the ventricles and are separated by the interatrial septum
• The ventricles are separated by the interventricular septum
• The right and left sides of the heart are functionally distinct, with the right side handling deoxygenated blood and the left side handling oxygenated blood

Blood Flow into the Atria

• The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava
  • The superior vena cava collects blood from the upper body (head, neck, and upper extremities)
  • The inferior vena cava collects blood from the lower body (trunk and lower extremities)
• The left atrium receives oxygenated blood from the lungs via the pulmonary veins
  • There are typically four pulmonary veins, two from each lung

Blood Flow out of the Ventricles

• The right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery for oxygenation
• The left ventricle pumps oxygenated blood to the body through the aorta for distribution to tissues and organs
• The left ventricle has a thicker muscular wall compared to the right ventricle due to the greater pressure required to pump blood throughout the systemic circulation

Blood Flow Through the Heart

Deoxygenated Blood Flow

• Deoxygenated blood enters the right atrium from the superior and inferior vena cava
• Blood flows through the tricuspid valve into the right ventricle during atrial contraction (atrial systole)
• The right ventricle pumps the deoxygenated blood through the pulmonary valve and into the pulmonary artery
• The pulmonary artery carries the blood to the lungs for oxygenation in the pulmonary capillaries

Oxygenated Blood Flow

• Oxygenated blood returns from the lungs via the pulmonary veins and enters the left atrium
• Blood flows through the mitral valve into the left ventricle during atrial relaxation (atrial diastole)
• The left ventricle pumps the oxygenated blood through the aortic valve and into the aorta during ventricular contraction (ventricular systole)
• The aorta distributes the oxygenated blood to the rest of the body through the systemic circulation

Coronary Circulation

• The heart muscle itself receives oxygenated blood via the coronary arteries, which branch off from the aorta just above the aortic valve
• Deoxygenated blood from the heart muscle is collected by the coronary veins and drains into the coronary sinus, which empties into the right atrium

Heart Valves and Unidirectional Flow

Valve Locations and Functions

• The heart contains four valves that ensure unidirectional blood flow: the tricuspid valve, pulmonary valve, mitral valve, and aortic valve
• The tricuspid valve is located between the right atrium and right ventricle
• The mitral valve is located between the left atrium and left ventricle
• The pulmonary valve is situated between the right ventricle and the pulmonary artery
• The aortic valve is located between the left ventricle and the aorta

Valve Opening and Closing Mechanisms

• The valves open and close in response to pressure changes within the heart chambers
• During ventricular relaxation (diastole), the AV valves (tricuspid and mitral) open to allow blood to flow from the atria into the ventricles
• During ventricular contraction (systole), the AV valves close to prevent backflow into the atria, while the semilunar valves (pulmonary and aortic) open to allow blood to flow into the pulmonary artery and aorta
• The closing of the valves produces the distinctive "lub-dub" heart sounds

Importance of Unidirectional Flow

• Unidirectional blood flow ensures efficient circulation and prevents the mixing of oxygenated and deoxygenated blood
• Valvular disorders, such as stenosis (narrowing) or regurgitation (leakage), can disrupt unidirectional flow and lead to reduced cardiac efficiency and potential complications

Atrioventricular vs Semilunar Valves

Atrioventricular (AV) Valves

• AV valves include the tricuspid and mitral valves, located between the atria and ventricles
• They prevent the backflow of blood from the ventricles into the atria during ventricular contraction (systole)
• AV valves are anchored to papillary muscles in the ventricles by chordae tendineae
• Chordae tendineae are fibrous strings that prevent the valves from inverting into the atria during ventricular contraction
• The tricuspid valve has three leaflets or cusps, while the mitral valve has two leaflets

Semilunar Valves

• Semilunar valves include the pulmonary and aortic valves, located between the ventricles and the great arteries (pulmonary artery and aorta)
• They prevent the backflow of blood from the arteries into the ventricles during ventricular relaxation (diastole)
• Semilunar valves have three crescent-shaped cusps that open and close in response to pressure changes
• Unlike AV valves, semilunar valves do not have chordae tendineae or papillary muscle attachments

Comparison of Valve Structure and Function

• Both types of valves ensure unidirectional blood flow through the heart, but their locations and specific structural features differ based on their unique roles in the cardiac cycle
• AV valves have chordae tendineae and papillary muscle attachments to prevent inversion, while semilunar valves rely solely on pressure gradients for opening and closing
• The number of leaflets or cusps differs between AV valves (tricuspid: three, mitral: two) and semilunar valves (pulmonary and aortic: three each)