The circulatory system

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  • The Circulatory System
    • Mass transport system
      • 1) Multicellular organisms have small SA:V ratio- need specialised transport systems to carry materials from exchange organs to body cells
      • 2) Made up of heart and blood vessels
      • 3) Heart pumps blood through blood vessels (veins, arteries, arterioles, capillaries)
      • 4) Blood transports respiratory gases, products of digestion, metabolic waste and hormones around the body
      • 5) Two circuits- one takes blood from heart to lungs, other takes blood from heart to rest of body
      • 6) Heart has own blood supply- left and right coronary arteries
    • Tissue fluid
      • Fluid that surrounds cells
      • Made of small molecules that leave blood plasma e.g oxygen, water, nutrients
      • Doesn't contain red blood cells/big proteins- too large to be pushed out of capillary walls
      • Cells take in oxygen/ nutrients from tissue fluid, release metabolic waste into it
    • Pressure filtration
      • 1) At start of capillary bed (nearest arteries) the hydrostatic pressure inside capillaries is greater than in the tissue fluid
      • 2) Difference in hydrostatic pressure means overall outward pressure forces fluid out of capillaries into spaces around cells- forms tissue fluid
      • 3) As fluid leaves, hydrostatic pressure reduces in capillaries, lower at venule end of capillary bed
      • 4) Water potential at venule end lower than that in tissue fluid
      • 5) Some water re enters capillaries from tissue fluid at venule end by osmosis


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