The Circulatory System: Structure

Introduction

• Focus: Structure of the circulatory system
• Importance: Understanding structure helps us understand function

Types of Circulatory Systems

Open Circulatory System

• Characteristics: Blood vessels are open, blood leaks among tissues
• Example: Insects like grasshoppers
• Traits: Found in small organisms, blood leaves blood vessels

Closed Circulatory System

• Characteristics: Blood remains in vessels, heart pumps blood throughout
• Example: Humans, earthworms
• Benefits: Supports larger organisms, specialized blood circulation

Human Circulatory System

Double Circulatory System

• Definition: Blood is pumped twice by the heart to different destinations
• Types:
  • Systemic Circulation: Blood from the heart to the body
  • Pulmonary Circulation: Blood from the heart to the lungs
• Process: Oxygenation cycle: Heart -> Lungs (oxygenated) -> Heart -> Body (deoxygenated) -> Heart -> Lungs

Heart Structure

External Structures

• Superior Vena Cava: Largest vein, brings blood to the heart
• Right Atrium: Top chamber, receives blood from vena cava
• Coronary Arteries: Supply heart’s own nutrients
• Right Ventricle: Lower chamber, muscular, pumps blood to lungs
• Aorta: Largest artery, distributes oxygenated blood
• Pulmonary Artery: Transports deoxygenated blood to lungs
• Pericardium: Thin protective layer around the heart
• Left Atrium: Receives oxygenated blood from lungs
• Left Ventricle: Thickest, pumps blood through the body
• Apex: Bottom point of the heart

Internal Structures

• Valves: Prevent backflow of blood
  • Tricuspid Valve: Between right atrium and ventricle
  • Pulmonary Valve: Controls blood flow from right ventricle to pulmonary artery
  • Mitral Valve: Between left atrium and ventricle
• Septum: Divides left and right sides of the heart
• Papillary Muscles: Control valves, prevent backflow
• Layers of the Heart: (Cross-section) :
  • Pericardium: Outer protective sac
  • Epicardium: Just inside pericardium
  • Myocardium: Muscular middle layer
  • Endocardium: Innermost layer

Blood Vessels

Types of Blood Vessels

• Arteries:
  • Function: Carry oxygenated blood away from the heart
  • Structure: Thick, elastic, narrow lumen
• Veins:
  • Function: Carry deoxygenated blood back to the heart
  • Structure: Thin, wide lumen, valves to prevent backflow
• Capillaries:
  • Function: Join arteries to veins, allow exchange of substances
  • Structure: Microscopic, one cell layer thick

Comparative Structure

• Arteries: Thick walls, high pressure, narrow lumen
• Veins: Thin walls, low pressure, wide lumen, presence of valves
• Capillaries: Only endothelial layer for easy diffusion

Summary of Key Terms

• Closed Circulatory System: Blood contained in vessels
• Double Circulation: Blood returns to heart twice (lungs and body)
• Pulmonary Circulation: Blood to and from the lungs
• Systemic Circulation: Blood to and from the body
• **Heart Chambers: **
  • 2 atria (upper chambers)
  • 2 ventricles (lower chambers)
• Pericardium: Outer heart layer
• Epicardium: Below pericardium
• Endocardium: Innermost heart layer
• Tricuspid Valve: Right atrium to ventricle
• Mitral Valve: Left atrium to ventricle
• Blood Vessel Types:
  • Arteries: Thick, narrow lumen
  • Veins: Thin, large lumen
  • Capillaries: Transport nutrients and wastes

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