blood, tissue fluid and lymph

• What is oncotic pressure?

  Tendency of water to move into the blood by osmosis
• What do plasma proteins generate in oncotic pressure?

  • An osmotic effect (for water to move into the blood by osmosis)
  • they give blood in capillaries a high solute potential and low water potential compared to the surrounding fluid
  • so they cause a water potential difference between the blood and tissue fluid OUTSIDE the blood
  • causes water to move into the blood by osmosis from the surrounding fluid
• What is the measurement of oncotic pressure?

  ALWAYS -3.3kPa
• What is oncotic pressure generated by?

  Plasma proteins
• What is hydrostatic pressure generated by?

  Heart contraction
• What are the measurements of hydrostatic pressure

  • Differs according to location
  • At arterial end- +4.6kPa
  • Venous end- +2.3 kPa
• What does it mean when pressure is positive?

  substances forced OUT OF blood capillaries- hydrostatic pressure exceeds oncotic pressure
• Substances transported in the blood?

  • Oxygen to and carbon dioxide from respiring cells
  • Digested food from the small intestine
  • Nitrogenous waste products from the cells to excretory organs
  • Chemical messengers
  • Platelets to damaged areas
  • Cells and antibodies involved in the immune response
  • Food molecules from storage compounds to cells that need them
• How does blood influence the temperature and pH of the body?

  • Maintains steady body temperature
  • Acts as a buffer, minimising pH changes
• Why does lymph form?

  • Some of the tissue fluid doesn’t return to the capillaries
  • 10% of it drains into lymph capillaries and is known as lymph
• How is the composition of lymph different to that of blood plasma and tissue fluid?

  • Has less oxygen
  • fewer nutrients
  • Fatty acids absorbed from the small intestine
• How is lymph transported through lymph vessels?

  By the squeezing of the body’s muscles
• How is the back flow of lymph prevented?

  Using one way valves
• What structures are lined along lymph vessels and what builds up in these structures?

  • Lymph nodes
  • Lymphocytes build up in lymph nodes when necessary and produce antibodies
• What is the role of lymph nodes?

  • Intercept bacteria and debris from the lymph
  • These are ingested by phagocytes found in the nodes
  • Major role in defence mechanisms of the body
• What are enlarged lymph nodes a sign of?

  That the body is fighting off an invasive pathogen
• what does it mean when pressure is negative in terms of oncotic and hydrostatic pressure?

  Water moves into the capillaries, into the blood- Oncotic pressure exceeds hydrostatic pressure.
• state the events taking place when hydrostatic pressure is generated

  • as blood flows through arterioles into capillaries, it is still under pressure from contractions of the heart
  • this pressure is hydrostatic pressure
  • +4.6kPa
  • higher than oncotic pressure (-3.3kPa) so fluid exits the capillaries
  • this fluid fills spaces between cells and is called tissue fluid, diffusion of substances takes place between cells and blood through tissue fluid
  • as the blood moves towards the venous end of the capillary, hydrostatic pressure falls to +2.3kPa, less than oncotic pressure at -3.3kPa
  • water moves back into the capillaries by osmosis

  
• how is tissue fluid different in composition to blood?

  • No RBCs
  • no plasma proteins