Circulatory system

• What is tissue fluid?

  Surrounds cells in tissues. Made from small molecules that leave blood plasma (oxygen, water & nutrients). No RBC or big proteins (too large to be pushed out capillary walls). Cells take in oxygen & nutrients from tissue fluid & release metabolic waste into it.
• Structure of arteries:

  Carry blood from heart to rest of body. Thick walls that are muscular & have elastic tissue to stretch & recoil as heart beats, which helps maintain high pressure. Inner lining (endothelium) is folded-allows artery to stretch, also helps maintain high pressure. All arteries carry oxygenated blood, except pulmonary arteries (take deoxygenated blood to lungs (smaller lumen)).
• Structure of arterioles:

  Arteries divide into smaller vessels. Form a network throughout body. Blood directed to different areas of demand by muscles inside arterioles, which contract to restrict blood flow or relax to allow full blood flow.
• Structure of capillaries:

  Arterioles branch into capillaries. Substances (e.g, glucose & oxygen) exchanged between cells & capillaries. Found near cells in exchange tissues-short diffusion pathway. Walls 1 cell thick. Large number of capillaries-increases surface area for exchange. Networks in tissue=capillary beds. Capillaries connect arterioles & venules together at capillary beds.
• What are venules?

  Small blood vessels that connect to veins.
• Structure of veins:

  Take blood back to heart under low pressure. Wider lumen, very little elastic or muscle tissue. Contain valves to prevent backflow of blood. Blood flow through veins helped by contraction of body muscles surrounding them. Carry deoxygenated blood except pulmonary veins (oxygenated blood to heart from lungs).
• How does an artery cope with high pressure?

  Stretches
• How does an artery cope with low pressure?

  Recoils
• Describe the start of capillary bed (nearest arteries):

  Hydrostatic pressure inside capillaries is greater than hydrostatic pressure in tissue fluid. Difference in pressure means overall outward pressure forces fluid out capillaries & into spaces around cells, forming tissue fluid. As fluid leaves, hydrostatic pressure reduces in capillaries, so hydrostatic pressure much lower at venule end of capillary bed (nearest to veins).
• Why is pressure highest at start of capillary bed?

  Left ventricle contracting & sending blood out heart at high pressure.
• Why is water potential at venule end of capillary end lower than tissue fluid's ?

  Fluid loss & increasing concentration of plasma proteins. Some water re-enters capillaries from tissue fluid at venule end by osmosis. Excess tissue fluid drained into lymphatic system-transports excess fluid from tissues & passes it back into circulatory system.
• Renal artery


  Carries blood from body to kidneys
• Renal vein


  Carries blood from kidneys to vena cava
• Vena cava 


  Carries blood from body to heart
• Aorta


  Carries blood from heart to body
• Pulmonary vein


  Carries blood from lungs to heart
• Pulmonary artery


  Carries blood from heart to lungs