Blood, tissue fluid and lymph

• what is blood?

  • the main transport medium of human circulatory system
• what is plasma?

  • yellow liquid which carries dissolved glucose, amino acids, mineral ions, hormones, red blood cells, transporting them around the body
• what is tissue fluid?

  • solution surrounding cells, distinct from blood
• what is lymph?

  • modified tissue fluid that is collected in the lymph system
• what is hydrostatic pressure?

  • the pressure created by water in an enclosed system
• what is oncotic pressure?

  • the tendency of water to move into the blood by osmosis as a result of the plasma proteins
• what is filtration pressure?

  • pressure affecting rate of filtration
• what does the process of ultrafiltration involve?

  • the process of water and dissolved substances leaving the blood plasma to the tissue fluid
• what does the process of reabsorption involve?

  • the process of waste products (carbon dioxide and left over oxygen) from the tissue fluid to the blood plasma
• what does the process of drainage involve?

  tissue fluid draining into lymph system
• what does blood transport?

  • oxygen and carbon dioxide to and from respiring tissues
  • digested food from the small intestine
  • nitrogenous waste products from cells to the excretory organs
  • chemical messages (hormones)
  • food molecules from storage compounds to cells that need them
  • platelets to damaged tissues
• what are the components of blood?

  • 55% plasma
  • 45% erythrocytes, platelets and levcocytes (white blood cells)
• how does tissue fluid form?

  plasma can leak out of capillaries through fenestration, forming tissue fluid
• what is the function of tissue fluid?

  surrounds cells in tissue and allows exchange of materials to and from cells, for example oxygen, glucose, urea and carbon dioxide
• what happens to tissue fluid?

  • some is reabsorbed into blood
  • the rest drains into lymphatic system to form lymph
• why is the hydrostatic pressure higher at the arteriole end of the capillary?

  • arteriolar end is closer to the heart so arrives with a higher hydrostatic pressure, so heartbeat has more influence to pressure than at the venule end
  • arteriole end is supplied by an artery, which has high pressure due to narrow lumen, and thick muscle and fibres maintaining pressure
  • as capillaries are very small there is an increase in resistance that slows down the blood in the capillary - decreasing hydrostatic pressure
• why is the water potential of the blood lower than that of the tissue fluid?

  plasma proteins are too large to leave the capillary, therefore since they are soluble they reduce the water potential of the blood, but not the tissue fluid - more dissolved substances and in blood in comparison
• why is there net movement of fluid from the blood to the tissue fluid at the arteriole end?

  effect of hydrostatic pressure (causing fluid to leave blood) is greater than the effect of oncotic pressure (causing fluid to be reabsorbed)
• why is there net movement of fluid into blood from the tissue fluid at the venue end?

  hydrostatic pressure in capillaries reduces due to increased resistance, effect of hydrostatic pressure (causing fluid to leave blood) is now lower than the effect of oncotic pressure (causing fluid to be reabsorbed)
• how is lymph formed?

  some tissue fluid drains into lymph vessels - this is as a result of a lower hydrostatic pressure inside the lymph vessels compared to tissue fluid
• what are the functions of the lymphatic system?

  • returns fluid to the blood
  • plays a role in the immune response
  • plays a role in absorption of fatty acids and fats from the digestive system
• how does the lymph eventually return to the blood?

  • through lymphatic vessels
  • by drawing into veins in the chest cavity
• what is the hydrostatic and oncotic pressure of tissue fluid and lymph?

  • hydrostatic - low
  • oncotic - higher (less negative)
• what is the direction of flow of tissue fluid?

  • tissue fluid reabsorption into blood plasma in capillaries
  • blood plasma (ultrafiltration) into tissues
  • tissue drainage into lymph
• what is the direction of flow of lymph?

  towards chest cavity where it returns to blood
• what causes the flow of blood?

  • heart beat (contracting)
  • contraction of smooth muscle - in vein (no influence from heart beat)
  • narrow lumen, recoil (artery) helping to maintain high pressure
• what causes the flow of tissue fluid?

  • osmosis to blood
  • hydrostatic pressure difference to lymph
• what causes the flow of lymph?

  • action of skeletal muscles
  • difference in hydrostatic pressure