Blood vessels

• OPEN

  In others, such on insects

  • there's a muscular pumping organ much like the heart
  • long, muscular tube lies under the dorsal (upper) surface of body
  • insects nave pores that allow blood from body to enter heart called Ostia
  • the heart then pumps blood towards head by peristalsis
  • forward end of heart (nearest to head) the blood pours into cavity
  • circulation continues when insect is at rest, but body movements can affect movement

  some larger insects, locusts, have open end tubes attached to heart; directing blood to active parts of the body where needed, such as leg
• Disadvantages of open circulatory

  • blood pressure is low
  • circulation can affect their movements; lack of movement
• CLOSED

  In larger animals blood stays entirely in blood vessels

  • tissue fluid, separate fluid, baths the cells of tissues
  • high blood pressure so blood flows quickly around body
  • more rapid delivery of oxygen
  • more rapid removal of carbon dioxide + waste
  • transport is independent of body movements
• Arteries

  • carries blood away from heart high blood pressure so has thick wall to be able to withstand high bp without bursting lumen and is relatively small in order to maintain high blood pressure
  • inner wall is folded to allow lumen to expand
• Arteries 2

  the wall consists of 3 layers

  • inner layer (tunica intima) consists of thin layer of elastic tissue to allow walls to stretch + recoil to maintain blood pressure
  • middle layer (tunica media) consists of thick layer of smooth muscle
  • outer layer (tunica adventitia) consists thick layer of collagen + elastic tissue ; provides strength to withstand blood pressure + recoil to maintain blood pressure
• Arterioles

  • small blood vessels that distributes blood from artery to capillaries
  • contains a layer of smooth muscle
  • contraction constrict the diameter of arteriole
  • increases the resistance of flow + reduces rate of flow
  • constriction of arteriole walls allows the blood to divert where regions in body are demanding for oxygen
• Capillaries allow exchange of materials between blood + tissue fluid

  • thin walls
  • lumen is very narrow- about the same diameter as red blood cells 7 micrometers; red blood cells squeeze against the capillary wall, helps transfer oxygen, it reduces the diffusion distance path to tissues
  • this also increases resistance + reduces rate of flow
  • walls consist of layers of flattened epithelial cells reducing diffusion distance of for materials being exchanged o walls are leaky, they allow red blood cell plasma + substances to leave blood
• Venules

  distributes blood from capillaries to small vessels

  • these collect from capillary bed + lead to veins
  • wall consists of thin layers of muscle + elastic tissue outside endothelium + thin outer layer has collagen
• veins

  • carries blood back to heart in low pressure so walls don't need to be thick
  • lumen, relatively large (low blood pressure)
  • thinner layer of collagen, muscle + elastic tissue than artery

  → don’t need to stretch or recoil or reduce the rate of flow

  since they're thin, they can flattened by surrounded skeletal muscle contraction of skeletal muscles applies pressure to blood; forcing blood to move determined by valves