Anatomy & Physiology Study Notes: Structure and Function of the Heart

Cardiovascular System: The Heart

Overview of the Heart

The heart is a muscular organ responsible for pumping blood throughout the body via the pulmonary and systemic circuits. Its structure and location are essential for understanding its function in the circulatory system.

• Location: The heart is located in the thoracic cavity, between the lungs, in a region called the mediastinum. It lies slightly to the left of the midline.

• Size: The average adult heart is about the size of a closed fist, approximately 12 cm long, 8-9 cm wide, and 6 cm thick.

• Base and Apex: The base of the heart is its broad superior portion, where the major blood vessels attach. The apex is the pointed inferior tip, which rests on the diaphragm.

• Function: The heart pumps blood through two main circuits: the pulmonary circuit (to the lungs) and the systemic circuit (to the rest of the body).

Pericardium and Pericardial Cavity

The heart is enclosed in a protective sac called the pericardium. This structure provides mechanical protection and reduces friction during heartbeats.

• Layers of the Pericardium:

  • Fibrous Pericardium: The tough, outer layer that anchors the heart to surrounding structures and prevents overfilling.

  • Serous Pericardium: A thinner, double-layered membrane consisting of:

    • Parietal Layer: Lines the internal surface of the fibrous pericardium.

    • Visceral Layer (Epicardium): Covers the external surface of the heart.

• Pericardial Cavity: The space between the parietal and visceral layers, filled with serous fluid to reduce friction as the heart beats.

• Purpose: Protects the heart, anchors it, and prevents friction during contraction.

Layers of the Heart Wall

The heart wall consists of three distinct layers, each with specialized functions.

• Epicardium: The outermost layer, also known as the visceral pericardium; provides a protective covering.

• Myocardium: The thick, middle layer composed of cardiac muscle tissue; responsible for the heart's contractile function.

• Endocardium: The innermost layer lining the heart chambers and valves; provides a smooth surface for blood flow and prevents clotting.

Chambers and Valves of the Heart

The heart contains four chambers and four main valves that regulate blood flow and prevent backflow.

• Chambers:

  • Right Atrium: Receives deoxygenated blood from the body via the superior and inferior vena cava.

  • Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary artery.

  • Left Atrium: Receives oxygenated blood from the lungs via the pulmonary veins.

  • Left Ventricle: Pumps oxygenated blood to the body via the aorta.

• Valves:

  • Atrioventricular (AV) Valves:

    • Tricuspid Valve: Between right atrium and right ventricle.

    • Bicuspid (Mitral) Valve: Between left atrium and left ventricle.

  • Semilunar Valves:

    • Pulmonary Valve: Between right ventricle and pulmonary artery.

    • Aortic Valve: Between left ventricle and aorta.

Septum of the Heart

The septum is a wall that divides the right and left sides of the heart, preventing the mixing of oxygenated and deoxygenated blood.

• Location: The septum runs vertically through the center of the heart.

• Types:

  • Interatrial Septum: Separates the right and left atria.

  • Interventricular Septum: Separates the right and left ventricles.

Summary Table: Heart Structure and Function

Component	Description	Function
Pericardium	Fibrous and serous layers	Protects and anchors the heart
Epicardium	Outer layer of heart wall	Protection
Myocardium	Middle muscular layer	Contraction and pumping
Endocardium	Inner lining	Prevents blood clotting
Chambers	Right/Left atria and ventricles	Receive and pump blood
Valves	AV and semilunar valves	Prevent backflow
Septum	Interatrial and interventricular	Separates heart sides

Example: The bicuspid (mitral) valve ensures that blood flows from the left atrium to the left ventricle without backflow, maintaining efficient circulation.