MH 071 Heart

Tricuspid Valve & Coronary Artery

The specimen shows the anatomical relationship between the right atrium and the right ventricle, with the tricuspid valve positioned between these chambers.

• Right Atrium (on the right side):
  • Receives deoxygenated venous blood from the systemic circulation
• Right Ventricle (on the left side):
  • Receives blood from the right atrium and pumps it into the lungs via the pulmonary arteries for oxygenation
• Heart Wall: Three layers characteristic of cardiac architecture:
  • Endocardium (Inner Layer): Endothelium supported by a thin layer of connective tissue
  • Myocardium (Middle Layer): Significantly thicker in the ventricle than in the atrium
  • Epicardium (Outer Layer):
    • Mesothelium: Simple squamous epithelium that covers the outer surface of the heart
    • Subepicardial Layer: Thin layer of dense irregular connective tissue with a much thicker layer of loose adipose connective tissue
• Tricuspid Valve:
  • Consists of three leaflets (only one is visible) that open and close during ventricular contraction to prevent backflow into the right atrium
• Right Coronary Artery
  • Major coronary vessel supplying oxygenated blood to the walls of both ventricles and the right atrium

Tricuspid Valve

The tricuspid valve typically consists of three leaflets that open and close during ventricular contraction, preventing backflow into the right atrium. The leaflets are connected to the ventricular wall by chordae tendineae and papillary muscles.

Leaflet Structure

This section passes through one leaflet of the tricuspid valve, though its chorda tendine or papillary muscle is not visible.

• Endothelium:
  • Simple squamous epithelium that covers both sides of the leaflet
  • Continuous with the lining of the heart chambers
• Dense Connective Tissue:
  • Forms the central core composed of collagen and elastic fibers
  • Continuous with the fibrous skeleton of the heart
  • Provides the tensile strength necessary to withstand the high pressures of ventricular contraction
• Avascular Structure:
  • Nutrients and oxygen diffuse from the blood in the heart chambers

Functional Mechanism:

When the right ventricle contracts, the papillary muscles also contract, maintaining tension on the chordae tendineae. This action prevents the leaflets from prolapsing back into the right atrium, ensuring one-way blood flow to the pulmonary circulation

Right Coronary Artery

The right coronary artery is a muscular artery composed of three concentric layers or “tunics.”

Structure:

The right coronary artery is a muscular artery composed of three concentric layers or “tunics.”

• Tunica Intima (Inner Layer):
  • Endothelium: Simple squamous epithelium that lines the vessel lumen
    • Poorly preserved in this specimen
  • Subendothelial Connective Tissue: Normally, a thin layer of collagen and elastic fibers (internal elastic lamina) that separates the intima from the media
• Tunica Media (Middle Layer):
  • Thickest layer composed of concentrically arranged smooth muscle cells with interspersed collagen and elastic fibers
• Tunica Adventitia (Outer Layer):
  • Dense irregular connective tissue composed of longitudinally arranged collagen and elastic fibers
  • Blends with the surrounding connective tissue

Pathological Findings:

The tunica intima is the thinnest layer in healthy tissue. This specimen shows pathological thickening due to the accumulation of smooth muscle cells and elastic tissue.

This finding is characteristic of atherosclerotic disease, which is most often associated with aging. The narrowing of the lumen can severely reduce coronary blood flow, potentially leading to myocardial ischemia.