Blood vessels

• What is the primary function of blood vessels?

  Transport blood throughout the body
• Why is understanding blood vessel structure important in OCR A Level Biology?

  It explains blood flow, pressure regulation, and nutrient exchange
• What are the five main types of blood vessels?

  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins
• What do arteries do?

  Carry blood away from the heart
• What is the role of arterioles?

  Regulate blood flow and pressure
• What is the function of capillaries?

  Sites of gas and nutrient exchange
• What do venules do?

  Collect blood from capillaries
• What is the function of veins?

  Return blood to the heart
• What are the structural adaptations of arteries?

  • Thick muscular walls
  • Narrow lumen
  • Elastic fibers
  • Smooth endothelium
• Why do arteries have thick walls?

  To withstand high pressure
• What is the significance of a narrow lumen in arteries?

  It helps maintain high pressure
• How do elastic fibers in arteries function?

  Allow expansion and recoil during heartbeats
• What is the function of arterioles?

  Control blood flow to capillaries
• What are the structural adaptations of arterioles?

  • Thinner walls than arteries
  • More smooth muscle
  • Less elastic tissue
• What is vasoconstriction?

  Narrowing of arterioles to reduce blood flow
• What is vasodilation?

  Widening of arterioles to increase blood flow
• What are the structural adaptations of capillaries?

  • One-cell-thick walls
  • Narrow lumen
  • Highly branched
  • Permeable walls
• Why are capillary walls one-cell thick?

  To allow rapid diffusion of substances
• What is the significance of a narrow lumen in capillaries?

  Increases gas exchange efficiency
• What are the structural adaptations of venules?

  • Thin walls
  • Some smooth muscle
  • Join to form larger veins
• What is the function of veins?

  Carry deoxygenated blood back to the heart
• What are the structural adaptations of veins?

  • Thin walls
  • Large lumen
  • Valves
  • Skeletal muscle pump
• Why do veins have valves?

  To prevent backflow of blood
• What is the function of the vena cava?

  Return blood from the body to the heart
• What are the adaptations for blood flow and pressure in the circulatory system?

  • Elastic recoil in arteries
  • Capillary exchange mechanisms
  • Venous return mechanisms
• How does elastic recoil in arteries help maintain blood flow?

  It maintains continuous flow during diastole
• What are the mechanisms of capillary exchange?

  • Diffusion
  • Ultrafiltration
  • Osmotic pressure
• What is ultrafiltration in capillaries?

  Hydrostatic pressure forces plasma out
• How do skeletal muscle contractions aid venous return?

  They push blood in veins forward
• How does inhalation assist venous return?

  Creates a pressure gradient toward the heart
• What should A* responses include in OCR A Level Biology?

  • Detailed descriptions of vessel structure & function
  • Comparative analysis between different vessels
  • Physiological context for adaptations
  • Examples of vessel functions in the body
  • Correct terminology usage
• What is a key approach for answering exam questions about blood vessels?

  Define roles, compare structures, explain mechanisms
• What is the tunica intima in arteries made of?

  Endothelial layer, connective tissue, elastic fibers
• What is the role of the tunica media in arteries?

  Strengthens arteries to withstand high pressure
• What is the function of collagen in the tunica adventitia?

  Protects blood vessels from damage
• Why do arterioles have a lower proportion of elastic fibers?

  They don’t experience major pressure fluctuations
• What is the significance of a large lumen in veins?

  Reduces resistance and allows easy blood flow
• What is absent in veins that is present in arteries?

  A pulse
• What is the role of venules in the circulatory system?

  Connect capillaries to veins
• Why do venules have few or no elastic fibers?

  Blood is at low pressure after capillaries