Capillaries Date:

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

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)?

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

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

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

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

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

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

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)

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

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

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

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

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

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