Heart Structure and Cardiac Cycle Study Notes

Heart Structure and Function

Coverings and Layers of the Heart Wall

The heart is protected and supported by several layers, each with distinct functions and associated pathologies.

• Pericardium: A double-walled sac that surrounds the heart, consisting of the fibrous pericardium (outer layer) and serous pericardium (inner layer).

• Epicardium: The outermost layer of the heart wall, also known as the visceral layer of the serous pericardium.

• Myocardium: The thick, muscular middle layer responsible for heart contractions.

• Endocardium: The innermost layer lining the heart chambers and valves.

Associated Pathologies:

• Pericarditis: Inflammation of the pericardium, causing chest pain and fluid accumulation.

• Myocarditis: Inflammation of the myocardium, often due to infection.

• Endocarditis: Infection of the endocardium, typically affecting heart valves.

Heart Valves

Heart valves ensure unidirectional blood flow through the heart chambers.

• Atrioventricular (AV) Valves: Tricuspid valve (right side) and Mitral valve (left side) separate atria from ventricles.

• Semilunar Valves: Pulmonary valve (right ventricle to pulmonary artery) and Aortic valve (left ventricle to aorta).

• Valve Actions: Open and close in response to pressure changes during the cardiac cycle.

Example: The mitral valve prevents backflow of blood from the left ventricle to the left atrium during ventricular contraction.

Cardiac Cycle

Phases of the Cardiac Cycle

The cardiac cycle describes the sequence of events in one heartbeat, including contraction and relaxation of the heart chambers.

• Atrial Systole: Atria contract, pushing blood into the ventricles.

• Ventricular Systole: Ventricles contract, ejecting blood into the pulmonary artery and aorta.

• Diastole: Both atria and ventricles relax, allowing chambers to fill with blood.

Key Actions:

• Valve opening and closing is coordinated with pressure changes in the chambers.

• Blood flows from areas of higher pressure to lower pressure.

Equation:

$\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$

Example: During ventricular systole, the pressure in the ventricles rises, causing the semilunar valves to open and blood to be ejected.

Summary Table: Heart Wall Layers and Functions

Layer	Location	Function	Associated Pathology
Pericardium	Surrounds heart	Protection, reduces friction	Pericarditis
Epicardium	Outer heart wall	Protection	Rarely affected
Myocardium	Middle layer	Contraction	Myocarditis
Endocardium	Inner layer	Lines chambers/valves	Endocarditis

Additional info: Academic context and definitions have been expanded for clarity and completeness.