Human Circulatory System: Anatomy and Blood Functions

The Human Circulatory System

The circulatory system is a complex network of organs that facilitates the movement of blood throughout the body to distribute nutrients and oxygen.

Anatomy of the Heart

The heart is a muscular organ located in the thorax between the lungs. It is roughly the size and shape of a fist and consists of three layers:

• Pericardium: The outer protective sac.
• Myocardium: The muscular middle layer.
• Endocardium: The inner lining.

The system also includes blood vessels: arteries, veins, and capillaries.

Internal Heart Structure

The heart is divided into four chambers:

• Atria (Top): Two chambers that act as receptors.
• Ventricles (Bottom): Two chambers that act as propulsion pumps.

Atrioventricular valves regulate blood flow, ensuring it moves in only one direction.

Heart Function and Blood

The primary function of the heart is to pump blood continuously. Blood is a red, viscous fluid composed of:

• Solid Components (40%):
  • Erythrocytes (Red Blood Cells): Carry oxygen.
  • Leukocytes (White Blood Cells): Immune defense.
  • Thrombocytes (Platelets): Clotting agents.
• Liquid Component: Plasma.

Cardiac Cycle

• Systole: The contraction phase that pushes blood into the vessels.
• Diastole: The expansion phase that allows the heart to fill with blood.

Circulation Types

• Pulmonary Circulation: The path of non-oxygenated blood to the lungs.
• Systemic Circulation: The journey of oxygenated blood to the body.

Vessels

• Arteries: Thick-walled, muscular vessels responsible for distributing oxygenated blood.
• Veins: Vessels responsible for collecting non-oxygenated blood.

Blood Cell Details

Erythrocytes

Disc-shaped cells without a nucleus containing hemoglobin. They capture O₂ from the lungs and transport it to cells, collecting CO₂ for removal.

Leukocytes

Variable cells with a nucleus and no pigment. They defend the body against disease using diapedesis (movement from blood into infected tissues). Types include lymphocytes and granulocytes.

Thrombocytes

Essential for blood clotting to prevent excessive bleeding. Hemophilia is a condition characterized by the inability to clot blood properly.

Cardiac Physiology Summary

• Diastole: Entry of blood into the heart.
• Systole: Output of blood from the heart.