B7 tissue fluid and skeletal system

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  • B7-Tissue fluid and the skeletal system
    • Chemical exchange
      • Between cells and capillaries
      • Arteries branch into capillaries
      • Capillaries have permeable walls, so substances can diffuse in and out
      • Networks of capillaries in tissues are called capillary beds
      • As blood passes through capillary beds small molecules (eg. water, glucose+ oxygen)
        • are forced out of the capillaries to form the tissue fluid, which surrounds the cells. These substances can then diffuse into the cells
      • Waste chemicals (eg. carbon dioxide and urea) diffuse out into the tissue fluid then capillaries
      • The tissue fluid allows cells to get the substances they need and get rid of waste without a capillary supplying every single cell
    • Jobs of the skeleton
      • Support
      • Move
      • Protect
    • Joints
      • Allow the bones to move
      • Bones are connected at joints by ligaments
        • Ligaments have a high tensile strength but are also slightly elastic- this means they help to stabilise joints but still allow movement
      • The ends of bones are covered with a smooth layer of cartilage to reduce friction between the bones
        • Cartilage can be slightly compressed so it acts as a shock absorber, like a cushion between bones
      • Membranes at some joints release synovial fluid to lubricate the joints, allowing them to move more easily by reducing friction
    • Movement
      • Muscles pull on bones to move them
      • Bones are attached to muscles by tendons ( which also attach muscles to other muscles)
      • Muscles move bones at a joint by contracting (becomes shorter
      • Tendons can't stretch much so when a muscle contracts a tendon pulls on the bone, transmitting the force from the muscle to the bone
      • Muscles can only pull on bones to move a joint. This is why muscles usually come in pairs (antagonistic pairs)
      • When one muscle in the pair contracts, the joint moves in one direction.
        • When the other muscle contracts, it moves in the opposite direction


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