Blood and Tissue Fluid

1. Blood and Tissue Fluid • explain the differences between blood, tissue fluid and lymph • describe how tissue fluid is formed from plasma;

2. Blood • Blood is liquid held in our blood vessels • It consists of: • Plasma: watery fluid containing dissolved oxygen, carbon dioxide, salt, glucose, fatty acids, amino acids, hormones and plasma proteins (proteins made in the liver) • Cells including red blood cells (erythrocytes) white blood cells (leucocytes) and platelets

3. Tissue Fluid • Similar to blood but does not contain most of the cells found in blood or any plasma proteins • Role is to transport oxygen and nutrients from the blood to the cells and to carry carbon dioxide and other wastes back to the blood

4. Task • Using Biology 1 p77-78, explain what tissue fluid is and how it is formed • Complete SAQ 9 & 10 on p78

5. How Tissue Fluid is Formed? • When blood is under high pressure in the artery before it enters the capillary, some blood fluid is pushed out of the capillaries though tiny gaps in the capillary wall, this is called tissue fluid. • The pressure that the blood is under due to the contraction of the heart is called hydrostatic pressure (a bit like fluid pushing up against the walls of a container)

6. What is in Tissue Fluid? • Plasma with dissolved nutrients and oxygen • The red blood cells, platelets and most of the white blood cells remain in the blood, with the plasma proteins. These are too large to fit through the gaps in the capillary wall

7. What does tissue fluid do? • It surrounds the body cells, so exchange of gases and nutrients can occur across the cell membranes (plasma membranes) • This exchange occurs by diffusion and facilitated diffusion • Oxygen and nutrients (e.g. glucose) enter the cells, carbon dioxide and other wastes (e.g. urea) leave the cells

8. How does the fluid get back into the blood? • The tissue fluid itself has some hydrostatic pressure and is pushed up against the capillaries allowing it to re-enter • The blood and the tissue fluid both contain solutes (dissolved substances) making their water potential more negative • The blood’s water potential is usually more negative so water tends to move from the tissue fluid back into the blood by osmosis, down the water potential gradient

9. Water potential: the analogy • Imagine 3 people, all of whom have a bank account with an overdraft (which means they can borrow money from the bank and make their account negative) Whom should give money to whom? Bill (Student) -$800 Jim (Computer Designer) $0 Shelly (Office Worker) -$475

10. Water potential: the analogy • Imagine 3 people, all of whom have a bank account with an overdraft (which means they can borrow money from the bank and make their account negative) Total = -$1275 /3 Bill (Student) -$425 Jim (Computer Designer) -$425 Shelly (Office Worker) -$425

11. Effective blood pressure = 3.2 - 2 = 1.2kPa Inside capillary (arterial end) fluid moves out of capillary as tissue fluid Total Hydrostatic pressure = 4.3-1.1 = 3.2kPa Total water potential = -3.3 – (-1.3) = -2kPa Arterial end High hydrostatic pressure in capillary Tissue fluid has higher hydrostatic pressure Tissue fluid has lower hydrostatic pressure Hydrostatic pressure = 4.3 Water potential = -3.3 Lower hydrostatic pressure in capillary Hydrostatic pressure = 1.1 Hydrostatic pressure = 1.1 Hydrostatic pressure = 1.6 Water potential = -1.3 Water potential = -3.3 Venous end Water potential = -1.3 Total Hydrostatic pressure = 1.6 -1.1 = 0.5kPa Effective blood pressure = 0.5 - 2 = -1.5kPa Inside capillary (venous end) fluid moves into capillary from tissue fluid Total water potential = -3.3 – (-1.3) = -2kPa

12. Movement back into the blood stream • At the venous (vein) end of the capillary, the blood has lost its hydrostatic pressure. The combined effect of the hydrostatic pressure in the tissue fluid and the osmotic force of the plasma proteins is sufficient to move fluid back into the capillary. • It carries with it any dissolved waste substances, such as carbon dioxide, that have left the cells

13. Lymph Complete the following questions using Biology 1 p78 • What determines the amount of fluid leaving the capillaries? • Explain why fluid flows out at the arterial end and in the venous end • What is tissue fluid? • What is lymph? • How does tissue fluid get into the lymphatic system? • What is oedema?

16. Carriage of Oxygen • describe the role of haemoglobin in carrying oxygen and carbon dioxide; • describe and explain the significance of the dissociation curves of adult oxyhaemoglobin at different carbon dioxide levels (the Bohr effect); • explain the significance of the different affinities of fetal haemoglobin and adult haemoglobin for oxygen.

17. Task • Using Biology 1 p80-84, produce a revision box for each of the following: • Haemoglobin dissociation curve • Carbon dioxide transport in the blood • The Bohr shift • Fetal Haemoglobin You are limited to one piece of A3 paper- you will need to read the information, decide what is important, and include it in the box, highlighting key terms

18. Haemoglobin Dissociation Curve Carbon Dioxide Transport The Bohr Shift Fetal Haemoglobin