Human Circulation and Heart Anatomy

Double Circulation

• Pulmonary (Minor) Circulation:

  • Carries CO₂-rich blood from the right ventricle to the lungs via the pulmonary artery.
  • Blood releases CO₂ and absorbs oxygen in the alveoli.
  • Oxygenated blood returns to the left atrium via pulmonary veins.

• Systemic (Major) Circulation:

  • Oxygenated blood leaves the left ventricle via the aorta, distributing to the body.
  • In capillaries, cells receive oxygen and nutrients; blood absorbs CO₂ waste.
  • Deoxygenated blood returns to the right atrium via the vena cavae, completing the cycle.

The Heart and Cardiac Cycle

• Heart Structure:

  • Two vena cavae bring CO₂-rich, oxygen-poor blood into the right atrium.
  • The right ventricle pumps blood to the pulmonary artery, carrying CO₂-rich, oxygen-poor blood to the lungs.
  • Four pulmonary veins bring oxygenated blood to the left atrium.
  • The aorta branches from the left ventricle, distributing oxygen-rich blood to the body.
  • Myocardium (heart muscle) composes the heart walls; a septum separates the left and right sides.

• Cardiac Cycle:

  • Heart pumps blood via rhythmic systole (contraction) and diastole (relaxation).
  • Each heartbeat represents a cardiac cycle:

• Atrial Systole: Atria contract, pushing blood into ventricles.

• Ventricular Systole: Ventricles contract, closing AV valves and forcing blood into the lungs and body via pulmonary and aorta arteries.

• Atrial and Ventricular Diastole: Atria and ventricles relax, allowing blood to fill and initiating a new cycle.

• Cardiac Alterations:

  • Valve problems can cause murmurs or arrhythmias, affecting heart rate.
  • Bradycardia (slow heart rate): <60 bpm
  • Tachycardia (fast heart rate): >100 bpm
  • Pulse rate measurement: Measure pulse for 30 seconds and multiply by 2. Typical range: 60-100 bpm.

Blood and Blood Vessels

• Blood Composition:

  • Viscous, red fluid circulating throughout the circulatory system.
  • Function: Transports oxygen and nutrients to cells; collects CO₂ and waste and delivers them to organs for removal.
  • Plasma (65%): Yellow liquid (water, minerals, proteins, waste).
  • Erythrocytes (Red Blood Cells):
    • No nucleus
    • Contain hemoglobin (iron gives red color)
    • Carry oxygen from lungs. (44%)
  • Leukocytes (White Blood Cells):
    • Larger than red blood cells
    • Defend against infections. (1% + platelets)
  • Platelets:
    • Cell fragments
    • Participate in blood clotting
    • (1% + Leukocytes)

• Blood Vessels:

  • Blood circulates through a closed system of arteries, veins, and capillaries.
  • Arteries:
    • Carry blood from the heart to the organs.
    • Branch into arterioles.
    • Thick, resilient walls for withstanding pumping pressure.
  • Veins:
    • Carry blood from the organs to the heart.
    • Venules merge into larger veins.
    • Thin, less elastic walls than arteries.
    • Contain valves preventing blood backflow.
  • Capillaries:
    • Microscopic vessels connecting arterioles and venules.
    • Extremely thin walls (single endothelial layer).
    • Facilitate gas, nutrient, and waste exchange between blood and cells.