Lecture Notes: The Circulatory System

Overview

• Lecture Topic: Structure of the Circulatory System
• Two-part series; this part focuses on structure, the next on processes
• Importance of understanding structure in relation to function in biology

Types of Circulatory Systems

• Open Circulatory System

  • Blood vessels are open; blood leaks out into tissues
  • Found in insects (e.g., grasshoppers)
  • Not suitable for large animals

• Closed Circulatory System

  • Blood remains inside blood vessels
  • Suitable for larger animals, e.g., humans, earthworms
  • Allows specialization of blood components
  • Blood only exits vessels in case of injury

Human Circulatory System

• Double Circulatory System
  • Heart pumps blood twice around the body
  • Involves systemic and pulmonary circulation

Systemic Circulation

• Blood circulation to the body
• Oxygenated blood from lungs to heart to body
• Blood collects CO2 as it moves through tissues

Pulmonary Circulation

• Circulation to the lungs
• Deoxygenated blood returns to heart, then to lungs to expel CO2

Heart Structure

• External Structures

  • Superior Vena Cava: Largest vein, brings blood to heart
  • Right Atrium: Top chamber, receives blood
  • Coronary Arteries: Supply heart itself with blood
  • Right Ventricle: Muscular, pumps blood to lungs
  • Aorta: Largest artery, distributes oxygenated blood
  • Pulmonary Artery: Carries blood to lungs
  • Pericardium: Protective membranous layer
  • Left Atrium/Ventricle: Chambers for oxygenated blood
  • Apex: Pointy tip of heart

• Internal Structures

  • Valves: Prevent backflow (Tricuspid, Mitral)
  • Papillary Muscles: Aid valve function
  • Septum: Divides heart into right (deoxygenated) and left (oxygenated)

Heart Layers

• Pericardium: Outer protective layer
• Epicardium: Inner layer beneath pericardium
• Myocardium: Muscular middle layer
• Endocardium: Innermost layer

Blood Vessels

• Arteries

  • Thick, muscular walls
  • Carry oxygenated blood at high pressure
  • Narrow lumen for efficient blood flow

• Veins

  • Thinner walls, larger lumen
  • Carry deoxygenated blood back to heart
  • Contain valves to prevent backflow

• Capillaries

  • Microscopic, one cell thick
  • Connect arteries and veins
  • Facilitate nutrient and waste exchange

Summary

• Closed and double circulatory systems in mammals
• Systemic vs. pulmonary circulation
• Heart's external and internal structures, including chambers and valves
• Differences between arteries, veins, and capillaries

Key Terms

• Closed System: Blood stays within vessels
• Double Circulation: Blood returns to heart twice
• Pulmonary/Systemic: Refers to lungs/body
• Ventricles/Atria: Lower/upper heart chambers
• Pericardium, Epicardium, Myocardium, Endocardium: Heart layers
• Arteries/Veins/Capillaries: Types of blood vessels

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• Next focus: Processes in the circulatory system
• Recommended to review diagrams and textbook for a better understanding of the heart's anatomy