Blood vessels

• What is the thick layer in artery walls made of?

  Collagen
• Why do arteries have a thick layer of collagen?

  To cope with high pressure from heart contractions
• What is the function of elastic tissue in arteries?

  To stretch and recoil with pressure changes
• Why is the inner endothelial layer of arteries folded?

  To stretch during increased pressure
• What role does smooth muscle play in arteries?

  Allows constriction and dilation for pressure changes
• What is the lumen of an artery like?

  Narrow
• What are the functions of arterioles?

  • Connect arteries to capillaries
  • Allow vasoconstriction and vasodilation
  • Regulate blood flow to tissues
• What happens during vasoconstriction in arterioles?

  Reduces blood flow to tissues
• What is the effect of vasodilation in arterioles?

  Increases blood flow to tissues
• What are the functions of venules?

  • Connect capillaries to veins
  • Have thin walls of muscle, elastic, and collagen
  • Wider lumen than arterioles to reduce resistance
• What aids venous return due to low blood pressure?

  Respiratory pump
• How does the muscular pump aid venous return?

  Contraction of skeletal muscles moves blood
• What prevents backflow during venous return?

  Valves
• Why do larger organisms need a transport system?

  • Cells are too far from the surface
  • Efficient nutrient supply and waste removal
  • Supports metabolic processes
• How does metabolic activity affect the need for a transport system?

  Active animals need more glucose and oxygen
• What happens to the surface area to volume ratio in larger organisms?

  It decreases
• What are the structural features of arteries related to their function?

  • Narrow lumen to maintain high pressure
  • Thick elastic tissue for expansion and recoil
  • Thick smooth muscle for constriction and dilation
  • Thick collagen for high pressure withstand
• What are the structural features of veins related to their function?

  • Wider lumen to reduce resistance
  • Thinner elastic tissue as no recoil needed
  • Thinner smooth muscle as no constriction needed
  • Valves to prevent backflow
• What are the structural features of capillaries related to their function?

  • Very narrow lumen (7 µm) for red blood cell squeezing
  • Single layer of flattened endothelial cells for short diffusion
  • Gaps between cells for material exchange
• What is the diameter of a capillary lumen?

  7 µm
• How does the structure of capillaries facilitate diffusion?

  Short diffusion distance due to narrow lumen
• What is the significance of gaps between endothelial cells in capillaries?

  Allows materials to enter and leave blood
• What should be included in a description of artery structure and function?

  • Thick collagen layer for high pressure
  • Elastic tissue for stretching and recoiling
  • Smooth muscle for constriction and dilation
  • Narrow lumen to maintain blood pressure