C3 - CO2, Bohr effect, tissue fluid

Bohr effect (4)

the movement of the oxygen dissociation curve to the right at a higher partial pressure of carbon dioxide, because at a given oxygen partial pressure, haemoglobin has a lower affinity for oxygen, when the partial pressure of carbon dioxide is higher

What does the Bohr effect account for? (2)

the unloading of oxygen from oxyhaemoglobin in respiring tissues, where the partial pressure of carbon dioxide is high and oxygen is needed

What does a low affinity for oxygen mean?

releases oxygen more easily

What does the Bohr effect do to an oxygen dissociation curve? (2)

causes shift to the right, allowing respiration to occur more readily

What happens when haemoglobin is exposed to an increase in oxygen partial pressure? (2)

haemoglobin absorbs oxygen rapidly at low partial pressures, but more slowly as partial pressure increases

What happens when oxygen partial pressures is high e.g. in the lung capillaries?

oxygen combines with the haemoglobin to form oxyhaemoglobin

What happens when oxygen partial pressure is low e.g. in respiring tissues?

oxygen dissociates from oxyhaemoglobin

What happens when carbon dioxide partial pressure is high?

haemoglobin has a lower affinity for oxygen, so it is less efficient at loading oxygen, and more efficient at unloading oxygen

How is carbon dioxide transported in the body? (3)

5% dissolved in plasma, 85% as hydrogen carbonate ions, 10% bound to haemoglobin as carbaminohaemoglobin

Explain the reactions that occur in the red blood cell (part 1)

carbon dioxide in the blood diffuses into the red blood cell

Explain the reactions that occur in the red blood cell (part 2) (3)

carbon dioxide that has diffused into the red blood cell takes part in a reversible reaction with water, producing carbonic acid, carbonic anhydrase catalyses this reaction

Explain the reactions that occur in the red blood cell (part 3)

the carbonic acid produced dissociates into hydrogen ions and bicarbonate ions

Explain the reactions that occur in the red blood cell (part 4) (2)

bicarbonate ions diffuse out of the red blood cell into the plasma, the chloride shift occurs when chloride ions diffuse into the red blood cell from the plasma

Explain the reactions that occur in the red blood cell (part 5) (3)

the hydrogen ions cause oxyhaemoglobin to dissociate into oxygen and haemoglobin, hydrogen ions combine with haemoglobin to produce haemoglobinic acid and oxygen , removing hydrogen ions preventing the pH decreasing in the red blood cell

Explain the reactions that occur in the red blood cell (part 6)

oxygen diffuses out of the red blood cell into tissues

What is the chloride shift?

the diffusion of chloride ions from plasma into the red blood cell, preserving electrical neutrality, as it balances the outflow of negative ions and maintains electrochemical neutrality

How do the reactions within a red blood cell explain the Bohr effect?

more carbon dioxide produces more hydrogen ions, so more oxygen is released from oxyhaemoglobin

How do these reactions within a red blood cell explain how carbon dioxide results in the delivery of oxygen to respiring tissues? (3)

more respiration means more carbon dioxide is present, so more oxyhaemoglobin dissociates, providing oxygen to respiring cells

Where does the exchange of materials between blood and body cells occur?

at the capillaries

What materials are transported from the blood to the body cells? (3)

plasma, solutes and oxygen

What materials are transported from the body cells to the blood? (3)

waste products, like carbon dioxide, urea in the liver

What are the adaptations of capillaries? (4)

thin and permeable walls, provide a large surface area for exchange of materials, blood flows very slowly through the capillaries, allowing time for exchange of materials

tissue fluid (3)

plasma without the plasma proteins, forced through capillary walls, bathing cells and filling the space between them

What is the function of tissue fluid? (2)

supplying cells with solutes like glucose, amino acids, fatty acids, salts, hormones and oxygen, removes waste made by cells

What is hydrostatic pressure?

pressure exerted by a fluid

What is osmotic pressure?

pressure generated by the osmotic effect of solutes in the capillary

What causes liquid to be pushed outwards from the capillary to the spaces between surrounding cells, in the arterial end of the capillary bed? (2)

high hydrostatic pressure, blood is under pressure from the pumping of the heart and muscle contraction in artery and arteriole walls

Why does plasma have a low solute potential and what effect does this have, in the arterial end of the capillary bed? (2)

due to the colloidal plasma proteins plasma has low solute potential, this causes water to be pulled back into the capillary by osmosis

Why is water and solutes forced out through the capillary walls into the spaces between cells, in the arterial end of the capillary bed?

the hydrostatic pressure is greater than the plasma’s solute potential

What favours the diffusion of solutes like glucose, oxygen and ions from the capillaries to the tissue fluid, in the arterial end of the capillary bed? (2)

they are used during cell metabolism, so their concentration in and around the cells is low

Why is the blood’s hydrostatic pressure lower than at the arterial end, at the venous end of the capillary bed? (2)

its volume has been reduced by fluid loss, and friction with the capillary walls resists its flow

Why are plasma proteins more concentrated in the blood, at the venous end of the capillary bed? (2)

because so much water has been lost, the solute potential of the remaining plasma is more negative as a result

Why does water pass back into the capillaries by osmosis, at the venous end of the capillary bed?

the osmotic force pulling water inwards is greater than the hydrostatic force pushing water outwards

What happens to the tissue fluid surrounding cells, at the venous end of the capillary bed? (5)

picks up carbon dioxide and other wastes, which diffuses down a concentration gradient from the cells, where they are made, into the capillaries, where they are less concentrated

Not all the fluid passes back into the capillaries, explain what happens to the remaining fluid, at the venous end of the capillary bed (3)

10% drains into the blindly ending lymph capillaries of the lymphatic system, most of the lymph fluid eventually returns to the venous system through the thoracic duct, which empties the left subclavian vein above the heart

lymph (2)

fluid absorbed from between cells into lymph capillaries, rather than back into capillaries