Overview of the Circulatory System

Introduction

• Imagery of a speck-sized creature in a bustling city traveling on highways.
• Body compared to a city, circulatory system compared to highways for transporting molecules.
• Analogous travel of oxygen molecule from the lungs to the toes through the circulatory system.

Components of the Circulatory System

Heart

• Central organ of the circulatory system, a muscular organ in the chest cavity.
• Functions as a powerful pump for moving blood through the body.
• Divided into four chambers:
  • Left atria and ventricle
  • Right atria and ventricle
• Oxygenated blood enters the left side; deoxygenated blood enters the right side.
• Chambers separated by valves that ensure one-way movement of blood.

Blood Vessels

• Network of arteries, veins, and capillaries acting as highways for blood.
• Human circulatory system is closed – blood stays within vessels.

Types of Blood Vessels

1. Arteries

   • Carry blood away from the heart.
   • Generally carry oxygenated blood (some exceptions).
   • High pressure; thick, muscular walls.
   • Pulse points where arteries are close to the skin (e.g., neck, wrists) used to measure heart rate.

2. Veins

   • Carry blood back to the heart.
   • Generally carry deoxygenated blood.
   • Thinner walls, lower pressure than arteries.
   • Valves ensure blood flows in one direction.
   • Textbook representations: veins in blue, arteries in red.

3. Capillaries

   • Smallest blood vessels, connecting arteries and veins.
   • Site of exchange for molecules like gases, nutrients, and waste.
   • Extremely thin (2-12 micrometers, thinner than a human hair).

Blood

• Specialized fluid tissue composed of plasma and cells.

Components of Blood

1. Plasma

   • Liquid part containing gases, proteins, hormones, nutrients.

2. Red Blood Cells (RBCs or Erythrocytes)

   • Transport oxygen.

3. White Blood Cells (WBCs or Leukocytes)

   • Defend against pathogens.

4. Platelets

   • Key role in blood clotting.

• Blood also transports heat from internal organs via plasma.

Blood Circulation System

Double Circulation

• Blood circulates through the heart twice.
• Pulmonary circulation: heart to lungs and back.
• Systemic circulation: heart to body and back.

Detailed Blood Flow

1. Pulmonary Circulation

   • Deoxygenated blood enters right atrium from superior and inferior vena cava.
   • Flows to right ventricle, which pumps it via pulmonary artery to lungs.
   • Gas exchange in lungs; blood becomes oxygenated.

2. Systemic Circulation

   • Oxygenated blood returns to left atrium via pulmonary veins.
   • Flows to left ventricle, which pumps it into aorta.
   • Blood distributed throughout the body.

Sounds of the Heart: "Lub Dub"

• Lub: Valves between atria and ventricles closing.
• Dub: Valves between ventricles and arteries closing.

Importance of Circulatory System

• Essential for the multicellular life’s sustenance.
• Discovered in the last 500 years; potential for future discoveries.

Summary

• Human circulatory system: heart acts as pump, blood vessels as highways.
• Blood circulates nutrients, gases, waste, and heat.
• Double circulation: pulmonary and systemic systems.
• Understanding has evolved, with future research holding promise for new discoveries.