Anatomy and Physiology of the Heart: Structure and Function

Heart Anatomy and Physiology

Overview of the Heart

The heart is a muscular organ responsible for pumping blood throughout the body via the circulatory system. It maintains the flow of oxygenated and deoxygenated blood through two main circuits: the pulmonary circuit and the systemic circuit.

• Pulmonary Circuit: Carries deoxygenated blood from the right side of the heart to the lungs for oxygenation, then returns oxygenated blood to the left side of the heart.

• Systemic Circuit: Distributes oxygenated blood from the left side of the heart to the rest of the body and returns deoxygenated blood to the right side.

Location, Size, and Orientation of the Heart

The heart is located in the thoracic cavity, specifically in the mediastinum, between the lungs and behind the sternum. It is slightly tilted so that the apex points to the left hip and the base faces the right shoulder.

• Location: Mediastinum, between the second and fifth intercostal spaces.

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

• Base: The broad, superior portion where major blood vessels attach.

• Apex: The pointed, inferior tip of the heart, directed downward and to the left.

Pericardium and Pericardial Cavity

The pericardium is a double-walled sac that surrounds and protects the heart. It consists of two main layers and encloses the pericardial cavity.

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

• Serous Pericardium: A thinner, inner layer divided into:

  • 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 during heartbeats.

Layers of the Heart Wall

The heart wall is composed of three distinct layers, each with specialized functions:

• Epicardium: The outermost layer, also known as the visceral layer of the serous pericardium; provides protection and contains blood vessels and nerves.

• Myocardium: The thick, middle layer made of cardiac muscle tissue; responsible for the contractile force of the heart.

• Endocardium: The innermost layer, composed of endothelial cells; lines the heart chambers and covers the heart valves.

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 (right side) and Mitral/Bicuspid (left side); prevent backflow into atria when ventricles contract.

  • Semilunar Valves: Pulmonary (right side) and Aortic (left side); prevent backflow into ventricles after contraction.

Septum of the Heart

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

• Interatrial Septum: Separates the right and left atria.

• Interventricular Septum: Separates the right and left ventricles.

• Location: Runs vertically through the center of the heart, from the base to the apex.

Summary Table: Heart Structure and Function

Structure	Location	Function
Pericardium	Surrounds heart	Protection, reduces friction
Epicardium	Outer heart wall	Protection, contains vessels
Myocardium	Middle heart wall	Contraction, pumping action
Endocardium	Inner heart wall	Lines chambers, covers valves
Right Atrium	Upper right chamber	Receives deoxygenated blood
Left Atrium	Upper left chamber	Receives oxygenated blood
Right Ventricle	Lower right chamber	Pumps blood to lungs
Left Ventricle	Lower left chamber	Pumps blood to body
Septum	Center of heart	Separates right and left sides