Heart Anatomy Overview

Overview of Heart Anatomy

General Characteristics of the Heart

• Size and Weight: Roughly the size of a fist, weighing approximately 300 grams.
• Function: Beats 60-80 times per minute, pumping 5-6 liters of blood throughout the body continuously.

Pericardial Sac

• Definition: A double-walled sac encasing the heart and the roots of great vessels (e.g., aorta, pulmonary trunk).
• Layers:
  • Fibrous Layer: The outer layer, made of dense irregular connective tissue, prevents overfilling and fixes the heart in the mediastinum.
  • Serous Layer: Comprised of two parts:
  • Parietal Layer: Lines the internal surface of the fibrous layer.
  • Visceral Layer: Adheres directly to the heart's surface.
• Pericardial Space: Area between the parietal and visceral layers, filled with pericardial fluid that acts as lubrication for heart movement.

Heart Chambers and Blood Flow

Chambers of the Heart

1. Right Atrium: Receives deoxygenated blood from the body.

   • Major Inflows: Superior vena cava (SVC) and inferior vena cava (IVC) for systemic blood, coronary sinus for blood from the myocardium.
   • Key Structure: Fossa ovalis - remnant of the fetal foramen ovale.

2. Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary trunk.

   • Tricuspid Valve: Connects right atrium to right ventricle, preventing backflow during systole.

3. Left Atrium: Receives oxygenated blood from the lungs through pulmonary veins.

   • Forms the posterior border of the heart.
   • Mitral/Bicuspid Valve: Regulates blood flow from left atrium to left ventricle.

4. Left Ventricle: Pumps oxygenated blood into the aorta.

   • Aortic Valve: Prevents backflow into the left ventricle during diastole.
   • Compared to the right ventricle, has a thicker myocardium due to higher arterial pressures (80-120 mmHg for systemic circulation compared to 10-20 mmHg for pulmonary circulation).

Heart Valves

• Types:
  • Atrioventricular Valves: Include the tricuspid and bicuspid (mitral) valves.
  • Semilunar Valves: Include aortic and pulmonary valves.
• Function:
  • Atrioventricular valves open during diastole and close during systole, preventing backflow.
  • Semilunar valves open to allow blood flow into the aorta or pulmonary arteries during ventricular contraction, closing to prevent backflow during diastole.

Great Vessels

• Aorta: Largest artery, distributing oxygenated blood to the systemic circulation.
• Pulmonary Arteries: Transport deoxygenated blood from the right ventricle to the lungs.
• Pulmonary Veins: Carry oxygenated blood back to the left atrium; notable for being the only veins in adults that carry oxygenated blood.

Coronary Circulation

• Definition: The system of blood vessels that supplies blood to the heart muscle itself.

• Major Coronary Arteries:

  • Right Coronary Artery (RCA): Supplies the right side of the heart.
  • Left Coronary Artery (LCA): Very short, bifurcates into:
  • Left Anterior Descending Artery (LAD): Supplies anterior part of the heart, interventricular septum; significant for supplying the left ventricle and the apex.
  • Left Circumflex Artery (LCX): Supplies the left lateral wall.

• Cardiac Veins: Major veins include the great cardiac vein (draining areas supplied by LAD), middle cardiac vein, and small cardiac vein.

• Coronary Sinus: Collects deoxygenated blood from cardiac veins and drains into the right atrium.

Summary of Blood Circulation

1. Deoxygenated blood: Right atrium → Tricuspid valve → Right ventricle → Pulmonary valve → Pulmonary arteries → Lungs.
2. Oxygenated blood: Lungs → Pulmonary veins → Left atrium → Mitral valve → Left ventricle → Aortic valve → Aorta → Systemic circulation.

Conclusion

• Overall, the heart functions as a pump that circulates blood throughout the body and lungs, with its anatomy designed to support efficient flow and pressure management in different parts of the circulatory system.