2. Capillaries
Date:

3. Learning Objectives
Recall diffusion as the movement of particles according to a concentration gradient
Evaluate models of diffusion
Interpret data on blood pressure using knowledge of ciculation

4. Exploring diffusion
Use the apparatus to investigate diffusion What is the effect of changing: The concentration of the chemical? The distance it must travel? The amount of energy (temperature or mixing)?

5. Modelling circulation
What makes an effective transport network? Compare circulation of red blood cells to a delivery driver transporting a package from the depot to someone’s front door

6. Modelling circulation
Draw particle diagrams to show how distance, concentration and pressure might change the rate of diffusion

8. Marking points BUT it is inaccurate because
It does not include red blood cells to carry oxygen/carbon dioxide
It doesn’t include glucose being transported to the cells
Pressure should be high entering the capillary be, but low leaving it
Muscle cells should be right next to the capillary
It doesn’t explain how oxygen and carbon dioxide pass between cells and blood
Muscle cells are the wrong shape
Marking points
The model is good/works well because it includes
Oxygen being supplied to cells
Carbon dioxide being removed from cells
Direction of blood flow
Reference to different pressure at beginning and end

9. List the sorts of things you would find in blood.
Contents of Blood

10. Tissue Fluid Artery Highest pressure Vein Lowest pressure
Capillary Network
Pressure changes here
Tissue fluid made here

11. Forming Tissue Fluid
Tissue fluid is the liquid that surrounds the cells, allowing for transport between blood and cells (e.g. Respiratory gases) - DIFFUSION
Capillary walls are partially permeable
Tissue fluid is the result of an interplay of:
1. Hydrostatic pressure
2. Osmosis

12. Forming Tissue Fluid
Hydrostatic pressure This is the pressure of the blood from heart contractions – it forces fluid out of the capillaries
Fluid moves out through tiny gaps in the capillary walls.
Dissolved gases and nutrients move with it
Larger plasma proteins and cells do not
(SOME hydrostatic pressure from
the tissue fluid forces fluids back
into the capillaries – but net
movement out)

13. Forming Tissue Fluid
2. Osmosis A net loss of water from the capillaries (due to hydrostatic forces) gives them a more negative water potential
Water moves down the water potential gradient into the capillaries

14. Arterial end of capillary
Forming Tissue Fluid
The movement of fluid is calculated as a net figure of hydrostatic pressure and osmotic pressure.
Hydrostatic pressure is much higher at the arterial end of the capillaries than the venous end
This means that the net movement is different at either end of the capillary network.
Arterial end of capillary

15. Forming Tissue Fluid
There is a net loss of fluid from the capillaries at the arterial end and a net gain at the venous.

17. Lymph Note that not all fluid passes back into the capillaries.
The excess output needs to be collected to avoid tissue swelling
This net excess is drained into the vessels of the lymphatic system – this fluid is known as lymph

18. Lymph
Lymph passes through the lymphatic system and drains back into the circulatory system
Lymph contains lymphocytes (type of white blood cell) which are made in lymph nodes.
Lymphocytes are part of the immune system and help to filter out foreign material from the lymph

19. Account for the shape of the graph
Key points:
Pressure from heart contractions
Pressure from muscle walls in arteries
Friction against the flow of blood
Wide network of capillaries spreads pressure
Less muscle in wall of veins