Blood Vessels

• Circulatory System

  • Human cells’ needs are met by our circulatory system.

  • Our system is described as a closed system.

  • Blood circulates from the heart through the arteries to the capillaries then to the veins and back to the heart.

  • There is a decrease in blood pressure as blood moves away from the heart.
• The five major functions of the cardiovascular system are:

  • Transporting oxygen and removing carbon dioxide

  • Transporting nutrients and removing wastes

  • Fighting disease

  • Transporting hormones

  • Regulating body temperature
• Blood Vessels

  • The blood vessels carry the blood around the body to supply organs

  with the nutrients they need and remove CO2 waste.
• There are 3 types of blood vessel:

  • Arteries (and arterioles)

  • Capillaries

  • Veins (and venules)
• • Arteries

  – carry blood away from the heart towards capillaries

  – under high pressure, therefore walls will be more muscular

  – Have an outer layer of connective tissue containing elastic fibres and a middle layer containing smooth muscle with more elastic fibres.

  – The elastic walls stretch and recoil to accommodate the surge of blood after each contraction of the heart.
• Arteries

  
  

  Carry blood away from the heart

  
  

  1.Thick outer wall

  • Collagen
  • Elastic fibres

  2. Thick middle muscle layer

  • Able to withstand high pressure

  3. Narrow lumen

  • Blood flow very rapid
• •The largest arteries e.g. the Aorta, have thick elastic walls which can stretch to accommodate the surge of blood after each contraction of the heart.
• Vasoconstriction & Vasodilation:

  To control blood flow , the smooth muscle surrounding arteries can contract causing vasoconstriction or relax causing vasodilation.
• • Veins

  – return blood to heart, from tissues

  – lower pressure, therefore less muscular

  – They have an outer layer of connective tissue containing elastic fibres but a much thinner muscular wall than arteries.

  – contain valves to prevent back flow of blood
• Capillaries

  – Allow exchange of substances with tissues through their thin walls.
• Vein

  1. Thin outer wall – Collagen – Elastic fibres

  2. Thin middle muscle layer – Low pressure of blood

  3. Wide lumen lumen – Blood flow slow

  4. Valves present - prevents the backflow of blood
• Valves

  • Prevent backflow of blood – Particularly in parts of body below heart

  • Not present in arteries.

  • Blood under lower pressure in veins

  • Faulty valves lead to varicose veins
• CAPILLARIES

  • Transport blood between arteries and veins

  • Form large networks (capillary beds)

  • Exchange of materials between blood and cells

  • Their walls are only one cell thick, allowing nutrients and waste to diffuse through with ease.
• Blood flows FROM the heart in ARTERIES.

  It then reaches CAPILLARIES where gases, waste and nutrients are exchanged with cells.

  It then reaches the VEINS which transports the blood BACK to the heart.