4.6 transfer of materials

• what is tissue fluid?

  substances containing small molecules (glucose, amino acids, oxygen) which are supplied to cells and removes waste.
• what are the 2 types of pressure involved in tissue fluid formation?

  • hydrostatic pressure - changes due to distance from heart
  • oncotic pressure - constant
• no exchange of material can take place in the artery and vein as the walls are too thick

  ions and small molecules cross capillary walls as they are small and walls are thin and have gaps.

  ions and small molecules leave capillary and form tissue fluid
• tissue fluid formation

  • in the arteriole end, hydrostatic pressure is higher than oncotic pressure
  • so molecules move down pressure gradient, into the tissue fluid (from the blood)
  • materials exchange between tissue fluid and cells
  • water and molecules in capillary reduces the hydrostatic pressure
  • oncotoic pressure stays the same
  • in the venuole end, hydrostatic pressure is lower than the oncotic pressure
  • so molecules move down pressure gradient into the blood
  • (from tissue fluid)
  • excess tissue fluid drians into lymph vessel - forming lymph.
• lymphatic system

  • network of lymph vessels
  • vessels lead to the heart - where lymph drains back into blood
  • no pump - has semi lunar valves
• structure of the capillary?

  • thin walls
  • permeable to small molecules
  • contains pores
  • has basement membranes
• why is there an absence of proteins in the tissue fluid?

  • too large
  • can't pass capillary wall
• role of the lymph vessel

  • drains excess tissue fluid
  • transports plasma proteins