Circulatory System Lecture Notes

Introduction

• Circulatory System: Also known as the cardiovascular system.
  • Components: Heart and blood vessels.
• Function: Delivers nutrients like oxygen to organs and tissues and removes waste like carbon dioxide.

Anatomy of the Heart

• Size and Location:
  • Size of a person's fist, cone-shaped.
  • Positioned in the mediastinum, slightly left, above the diaphragm, behind the sternum, in front of the vertebral column, between the lungs, and protected by the ribs.

Pericardium

• Serous Pericardium: Double-walled sac surrounding the heart.
  • Parietal Layer: Outer layer, adheres to the fibrous pericardium.
  • Visceral Layer (Epicardium): Inner layer, adheres to the heart.

Heart Layers

• Epicardium: Outer layer.
• Myocardium: Muscular middle layer, contains:
  • Cardiac muscle cells and connective tissue fibers (fibrous cardiac skeleton).
  • Coronary vessels for blood supply.
• Endocardium: Innermost layer, lines heart chambers and valves.

Blood Flow Through the Heart

• Right Side: Deoxygenated blood flow:
  • Enters via superior/inferior vena cava or coronary sinus into right atrium.
  • Passes through tricuspid valve to right ventricle.
  • Exits through pulmonary valve to pulmonary arteries.
  • Heads to lungs for oxygenation.

Pulmonary Circulation

• Blood becomes oxygenated, moves from pulmonary capillaries to pulmonary veins, enters left atrium.

• Left Side: Oxygenated blood flow:

  • Passes through mitral valve to left ventricle.
  • Exits through aortic valve to aorta, begins systemic circulation.

Systemic Circulation

• Blood delivers oxygen to body tissues, returns deoxygenated to the heart via vena cavas.

Heart Sounds and Function

• S1 (Lub): Tricuspid and mitral valves close, ventricles contract (systole starts).
• S2 (Dub): Aortic and pulmonary valves close (systole ends, diastole begins).
• Cardiac Output: Blood volume pumped by ventricles per minute.
• Venous Return: Blood volume returning to atria.

Blood Vessel Structure

• Layers/Tunics:
  • Tunica Intima: Endothelial layer, minimizes friction.
  • Tunica Media: Smooth muscle and elastin, regulates vasoconstriction/dilation.
  • Tunica Externa: Collagen fibers, provides support and anchoring.

Vessel Types and Functions

• Elastic Arteries: Aorta and main branches, stretch to absorb pressure changes.
• Arterioles: Control blood flow to capillaries via vasoconstriction/dilation.
• Capillaries: One cell thick, facilitate gas/nutrient exchange.
• Veins/Venules: Valves prevent backflow, high volume, low pressure.

Blood Distribution

• Pulmonary Circulation: 10% of blood.
• Heart Chambers: 5% of blood.
• Systemic Circulation:
  • Arteries: 15% (to brain, heart, kidneys, gastrointestinal organs, muscles, skin).
  • Capillaries: 5%.
  • Veins: 65%.

Conclusion

• Blood Flow Recap: Pulmonary and systemic circulation cycles.
• Additional Resources: Osmosis.org for deeper insights, quizzes, and flashcards.

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