Intracellular or tissue fluid

• where does exchange between the blood and the body cells happen?

  at the capillaries
• what moves from the blood to the cells?

  • plasma solutes
  • oxygen
• what moves from the cells to the blood?

  • waste products (e.g. carbon dioxide)
  • in the liver, urea move from the cells to the blood
• how are capillaries well adapted to allow exchange of materials?

  • they have thin, permeable walls
  • they provide a large surface area for exchange of materials
  • blood flows very slowly through capillaries, allowing time for exchange of materials
• how does fluid from the plasma transport into the capillaries?

  fluid from the plasma is forced through the capillary walls and, as tissue fluid, bathes the cells, supplying them with solutes such as glucose, amino acids, fatty acids, salts, hormones and oxygen
• what does tissue fluid do?

  it removes waste made by the cells
• what does the diffusion of solutes in and out of the capillaries relate to?

  it relates to the blood’s hydrostatic pressure and solute potential
• what is this an image of?

  formation of tissue fluid and lymph in a capillary bed

  
• what happens to the blood at the arterial end of a capillary?

  • blood is under pressure from the pumping of the heart and muscle contraction in artery and arteriole wals
  • the high hydrostatic pressure pushes liquid outwards from the capillary to the spaces between the surrounding cells
• what happens to the plasma at the arterial end of a capillary bed?

  plasma is a solution and its low solute potential, due mainly to collodial plasm proteins, tends to pull water back into the capillary by osmosis
• what happens to water and solutes at the arterial end of a capillary bed?

  the hydrostatic pressure is greater than the plasma’s solute potential, so water and solutes are forced out through the capillary walls into spaces between the cells
• what happens to solutes at the arterial end of a capillary bed?

  • solutes, such as glucose, oxygen and ions are used during cell metabolism so their concentration in and around the cells is low, but in the blood is higher
  • this favours diffusion from the capillaries to the tissue fluid
• why is the blood’s hydrostatic pressure lower at the venous end of the capillary bed compared to the arterial end?

  as its volume has been reduced by fluid loss and because friction with the capillary walls resists its flow
• what happens to the plasma at the venous end of a capillary bed?

  • the plasma proteins are more concentrated in the blood because so much water has been lost
  • the solute potential of the remaining plasma is, therefore, more negative
  • the osmotic force pulling water inwards is greater than the hydrostatic force pushing water outwards so water passes back into the capillaries by osmosis
• what happens to the tissue fluid at the venous end of a capillary bed?

  tissue fluid surrounding cells picks up carbon dioxide and other wastes, which diffuses down a concentration gradient from the cells, where they are made, and into the capillaries, where they are less concentrated
• what happens to all the fluid at the venous end of a capillary bed?

  • not all of the fluid passes back into the capillaries
  • about 10% drains into the blindly-ending lymph capillaries of the lymphatic system
  • most of the lymph fluid eventually returns to the venous system through the thoracic duct, which empties into the left subclavian vein above the heart
• what is lymph formed from?

  from excess tissue fluid
• what is tissue fluid?

  • plasma without the plasma proteins, forced through capillary walls, bathing cells and filling the spaces between them
  • tissue fluid = plasma - plasma proteins
• what does this image show?

  a diagram of opposing forces in a capillary bed

  
• where is plasma located?

  in blood vessels
• where is tissue fluid located?

  surrounding body cells
• where is lymph located?

  in lymph capillary vessels
• where are cells associated with plasma?

  • erythrocytes (red blood cells)
  • granulocytes (white blood cells)
  • lymphocytes (white blood cells)
• what cells are associated with tissue fluid?

  • granulocytes
  • lymphocytes
• what cells are associated with lymph?

  • granulocytes
  • lymphocytes
• what are the respiratory gases in plasma?

  more oxygen, less carbon dioxide
• what are the respiratory gases in tissue fluid?

  less oxygen, more carbon dioxide
• what are the respiratory gases in lymph?

  less oxygen, more carbon dioxide
• how much nutrients are there in plasma?

  lots
• how much nutrients are there in tissue fluid?

  not a lot
• how much nutrients are there in lymph?

  not a lot
• does plasma have large protein molecules?

  yes
• what is the water potential like in plasma?

  low
• what is the water potential like in tissue fluid?

  high
• what is the water potential like in lymph?

  high