Ch.18 pt.1: Cardiovascular System: Heart Anatomy and Circulation

Heart Anatomy and the Cardiovascular System

Pulmonary and Systemic Circuits

The heart functions as a dual pump, maintaining two major circulatory pathways: the pulmonary and systemic circuits. These circuits ensure the delivery of oxygen and nutrients and the removal of waste products from body tissues.

• Pulmonary Circuit: The right side of the heart receives oxygen-poor blood from the body and pumps it to the lungs. In the lungs, blood releases carbon dioxide (CO2) and picks up oxygen (O2).

• Systemic Circuit: The left side of the heart receives oxygen-rich blood from the lungs and pumps it to the rest of the body, delivering oxygen and nutrients to tissues.

• Key Chambers:

  • 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.

Size, Location, and Orientation of the Heart

The heart is a muscular organ located in the thoracic cavity, specifically within the mediastinum. Its size and position are important for its function and clinical assessment.

• Size: Approximately the size of a closed fist; weighs less than 1 pound.

• Location:

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

  • Rests on the superior surface of the diaphragm.

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

  • Anterior to the vertebral column and posterior to the sternum.

• Orientation:

  • The base (posterior surface) leans toward the right shoulder.

  • The apex points toward the left hip.

  • The apical impulse can be palpated between the fifth and sixth ribs, just below the left nipple.

Visual Representation: Location of the Heart in the Mediastinum

The heart is centrally located in the chest, protected by the rib cage. The diagram shows its position relative to the midsternal line, second rib, diaphragm, and sternum. The apical impulse is a clinical landmark for assessing heart function.

Key Terms and Definitions

• Mediastinum: The central compartment of the thoracic cavity, containing the heart, great vessels, trachea, and other structures.

• Apical Impulse: The point of maximal impulse (PMI) where the heartbeat can be felt most strongly on the chest wall.

• Pulmonary Circuit: The pathway of blood from the right ventricle to the lungs and back to the left atrium.

• Systemic Circuit: The pathway of blood from the left ventricle to the body tissues and back to the right atrium.

Example: Blood Flow Sequence

Blood enters the right atrium from the body (systemic circuit), passes to the right ventricle, and is pumped to the lungs (pulmonary circuit). Oxygenated blood returns to the left atrium, moves to the left ventricle, and is pumped to the body (systemic circuit).

Additional info:

• The pulmonary circuit is a low-pressure system, while the systemic circuit operates under higher pressure to deliver blood throughout the body.

• The anatomical position of the heart is crucial for procedures such as auscultation and imaging.