Blood and Tissue Fluid

• explain the differences between blood, tissue fluid and lymph

• describe how tissue fluid is formed from plasma;

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

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

Task

• Using Biology 1 p77-78, explain what tissue fluid is and how it is formed

• Complete SAQ 9 & 10 on p78

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)

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

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

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

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)

Bill (Student)-$800

Shelly (Office Worker)-$475

Jim (Computer Designer)$0

Whom should give money to whom?

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)

Bill (Student)-$425

Shelly (Office Worker)-$425

Jim (Computer Designer)-$425

Total = -$1275 /3

High hydrostatic pressure in capillary

Lower hydrostatic pressure in capillary

Tissue fluid has lower hydrostatic pressure

Tissue fluid has higher hydrostatic pressure

Hydrostatic pressure = 1.1

Hydrostatic pressure = 4.3

Water potential = -1.3

Water potential = -3.3

Total Hydrostatic pressure = 4.3-1.1 = 3.2kPa

Total water potential = -3.3 – (-1.3) = -2kPa

Effective blood pressure = 3.2 - 2 = 1.2kPa

Inside capillary (arterial end) fluid moves out of capillary as tissue fluid

Hydrostatic pressure = 1.1

Hydrostatic pressure = 1.6 Water potential = -1.3

Water potential = -3.3

Total Hydrostatic pressure = 1.6 -1.1 = 0.5kPa

Total water potential = -3.3 – (-1.3) = -2kPa

Effective blood pressure = 0.5 - 2 = -1.5kPa

Inside capillary (venous end) fluid moves into capillary from tissue fluid

Arterial end

Venous end

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

LymphComplete the following questions using Biology 1 p78

1. What determines the amount of fluid leaving the capillaries?2. Explain why fluid flows out at the arterial end and in the venous end3. What is tissue fluid?4. What is lymph?5. How does tissue fluid get into the lymphatic system?6. What is oedema?

Feature Blood Tissue Fluid Lymph

Cells Some phagocytic white blood cells

Proteins Some proteins

Fats Some transported as lipoproteins

Some/none More than in blood (absorbed from lacteals in intestine-villi)

Glucose 80-120mg per 100ml

More/less More/less

Amino Acids More/less More/less More/less

Oxygen More/less More/less More/less

Carbon dioxide Lot/little More/less More/less

Feature Blood Tissue Fluid Lymph

Cells Erythrocytes, leucocytes and platelets

Some phagocytic white blood cells

Lymphocytes

Proteins Hormones and plasma proteins

Some hormones, proteins secreted by body cells

Some proteins

Fats Some transported as lipoproteins

None More than in blood (absorbed from lacteals in intestine-villi)

Glucose 80-120mg per 100ml

Less (absorbed by body cells)

Less

Amino Acids More Less (absorbed by body cells)

Less

Oxygen More Less (absorbed by body cells)

Less

Carbon dioxide Little More (released by body cells

More

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.

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 HaemoglobinYou 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

Haemoglobin Dissociation Curve Carbon Dioxide Transport

The Bohr Shift Fetal Haemoglobin