Cardiovascular System Histology (Part 1)

Cardiovascular System Histology (Part 1)

• The circulatory system carries blood and substances to all body tissues. The total length of blood vessels in an adult is estimated at 100,000 to 150,000 km.
• The cardiovascular system includes the blood vascular system.
• The blood vascular system consists of: heart, arteries, capillaries, and veins.

Heart Structure and Function

• The heart's four chambers (right and left ventricles, right and left atria) contract rhythmically, pumping blood through the pulmonary and systemic circulation.
• The right ventricle pumps blood to the pulmonary circulation, while the left ventricle pumps blood to the systemic circulation.
• The right and left atria receive blood from the body and pulmonary veins, respectively.

Heart Wall Layers

• The heart wall consists of three layers:
  • Endocardium: a thin inner layer of endothelium and connective tissue. Includes the heart's impulse-conducting system.
  • Myocardium: a thick layer of cardiac muscle, arranged spirally around the heart chambers. It's thicker in the ventricle walls (especially left). This is needed for the strong pumping action.
  • Epicardium: a simple squamous mesothelium (a thin layer of cells) supported by connective tissue. This layer corresponds to the visceral pericardium. This cushions the heart and prevents friction.

Additional Heart Structures

• The heart also includes dense fibrous connective tissue forming parts of the interventricular and interatrial septa, as well as surrounding the heart valves. This tissue anchors the valves and acts as electrical insulation.
  • Sinoatrial (SA) node: The pacemaker located in the right atrium.
  • Atrioventricular (AV) node,
  • AV bundle (of His),
  • Subendocardial conducting network (Purkinje fibers): These cells conduct electrical impulses that cause the heart to contract.

Vascular Wall Tissues

• Blood vessel walls (excluding capillaries) have endothelial linings with smooth muscle and connective tissue.
• The amount and arrangement of these tissues depend on factors like blood pressure and metabolic needs.
• Endothelium acts as a semipermeable barrier between blood plasma and interstitial tissue fluid.
• Vascular endothelial cells are polygonal and elongated, with their axis aligned with blood flow.
• Smooth muscle is present in vessel walls larger than capillaries and are arranged helically. This helps regulate blood pressure.
• Connective tissue components, including collagen and elastic fibers, provide structure and resilience to the vessel walls. Elastic tissue is more prominent in large arteries.