Heart Anatomy and Physiology: Pulmonary & Systemic Circuits, Location, and Coverings

Pulmonary and Systemic Circuits

Overview of Heart as a Transport System

The heart functions as a dual pump, facilitating the circulation of blood through two distinct circuits: the pulmonary and systemic circuits. Each side of the heart is responsible for a specific circuit, ensuring efficient oxygenation and nutrient delivery throughout the body.

• Right side of the heart: Receives oxygen-poor blood from body tissues.

• Pumps blood to the lungs to eliminate CO2 and acquire O2 via the pulmonary circuit.

• Left side of the heart: Receives oxygenated blood from the lungs.

• Pumps blood to body tissues through the systemic circuit.

Chambers of the Heart and Their Roles

The heart contains four chambers, each with a specific function in the circulation process.

• Right atrium: Receives blood returning from the systemic circuit.

• Left atrium: Receives blood returning from the pulmonary circuit.

• Right ventricle: Pumps blood through the pulmonary circuit.

• Left ventricle: Pumps blood through the systemic circuit.

Example: The right ventricle sends deoxygenated blood to the lungs, while the left ventricle sends oxygenated blood to the rest of the body.

Location and Orientation of the Heart

Physical Characteristics and Position

The heart is a muscular organ, roughly the size of a fist and weighing less than one pound. Its location and orientation are crucial for its function.

• Located in the mediastinum, between the second rib and fifth intercostal space.

• Sits on the superior surface of the diaphragm.

• Approximately two-thirds of the heart lies to the left of the midsternal line.

• Positioned anterior to the vertebral column and posterior to the sternum.

Example: The apical impulse can be felt at the fifth intercostal space, just below the left nipple.

Coverings of the Heart

Structure and Function of the Pericardium

The heart is enclosed by a protective sac called the pericardium, which consists of two main layers and serves several vital functions.

• Fibrous pericardium (superficial): Anchors the heart to surrounding structures and prevents overfilling.

• Serous pericardium (deep, two-layered):

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

  • Visceral layer (epicardium): Covers the external surface of the heart.

• The two layers are separated by a fluid-filled pericardial cavity, which decreases friction during heart activity.

Clinical Conditions Related to the Pericardium

• Pericarditis: Inflammation of the pericardium, causing roughened membrane surfaces and a pericardial friction rub (audible with a stethoscope).

• Cardiac tamponade: Accumulation of excess fluid in the pericardial space, compressing the heart and impairing its pumping ability. Treatment involves removal of fluid, typically with a syringe.

Additional info: The pericardium is essential for maintaining the heart's position and reducing mechanical stress during contraction and relaxation.