Carriage of O2 and CO2 in the blood

Question 1

How is oxygen carried?

Answer 1

Carried in two forms

1. Dissolved in blood
2. Combined with Hb

Question 2

Oxygen dissolved in blood- what is it affected by?

Answer 2

Amount of gas in solution proportional to temperature (more dissolves at low temperature)

Question 3

What is the equation for the volume of oxygen in blood at 37 degrees?

Answer 3

Volume of O2 = 0.0232 x PO2

0.0232 is a constant

Question 4

Does gas dissolve better in cold or hot water?

Answer 4

Amount of gas in solution varies with T and the lower the T the more gas dissolves- more in cold than hot water

Question 5

What is the equation for oxygen saturation?

Answer 5

HbO2/ HHb+HbO2

Question 6

Volume of oxygen equation

Answer 6

SO2 x Hb x 1.39 (Hufner constant)

Question 7

What is the Hufner constant?

Answer 7

Hufner constant- amount of oxygen Hb can carry

Question 8

What is the structure of Hb?

Answer 8

Primary – 141-146 amino acids per chain
Secondary – globular structure
Tertiary – ‘crevice’ for haem and O2 binding
Quaternary – 4 chains (HbA = 2 x a and 2 x b)

Question 9

How many global chains, ahem groups, iron atoms and how many oxygen atoms it binds to?

Answer 9

• 4 x globin chains
• 4 x haem groups
• 4 x iron atoms
• and binds 4 x O2 molecules

Question 10

What state can oxygen bind to Hb?

Answer 10

In R ‘relaxed’ form O2 can access binding site.

Question 11

What state is oxygen pushed put of Hb?

Answer 11

In T ‘tense’ form O2 pushed out.

Question 12

What does diphosoglycerate do?

Answer 12

Diphosphoglycerate (DPG)- compound found in RBC which is broken down in glycolysis to provide energy- can control the curve by shifting to make oxygen more available.

Question 13

Abnormal Hb- absent global chain

Answer 13

Thalassaemia- genetic abnormality
Other globin chains used; often can’t survive
Thalassemia- genetic abnormality when chains (alpha or beta) of Hb can’t be produced- alphas= more severe (often foetus doesn’t make it to birth) patients with beta tend to keep their foetal Hb throughout

Question 14

Why is alpha thalassaemia more fatal?

Answer 14

Alpha chains are present in adult and foetal Hb.

Question 15

Abnormal Hb- defective global chain

Answer 15

HbS (sickle cell disease)

Single amino-acid defect; red cells sickle at low PO2

Question 16

Abnormal Hb- defective Fe atom

Answer 16

Methaemoglobin

Drug induced; metHb does not carry oxygen- oxygen carrying capacity reduced

Question 17

Abnormal Hb- wrong ligand

Answer 17

CO Hb

Smoking/house fires; CO blocks O2 binding site

Question 18

What affects Hb- O2 dissociation

Answer 18

Temperature, pH change (Bohr effect) and DPG

Question 19

Buffer

Answer 19

A buffer is a solution that can minimise changes in the free H+ concentration
and therefore in pH ( pH= - log10 [H+] )

acid ⇌ H+ + base
e.g. H2CO3 ⇌ H+ + HCO3-

Question 20

Blood buffer systems include what?

Answer 20

Include proteins – carboxyl and amino groups at each end of the chain, and basic/acidic side chains of amino acids

Question 21

What 3 ways is carbon dioxide carried?

Answer 21

Dissolved blood, carbamino compounds and carbonic acid/ bicarbonate

Question 22

CO dissolved in blood is dependent on what?

Answer 22

Temperature

Question 23

Carbamino compounds- what do they do?

Answer 23

• Bound to R-NH2 groups on proteins

* Includes terminal amino group and side chains of lysine and arginine

Question 24

What is catalyses carbon dioxide and water to dorm carbonic acid?

Answer 24

Carbonic anhydrase

Question 25

How do RBC manage the amount of H+ and HCO3- ions?

Answer 25

CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-

HCO3- - Pumped out of red cell in exchange for a chloride ion (Hamburger shift)
H+ buffered by Hb

Question 26

What is the Haldane effect?

Answer 26

Ability of deoxygenated blood to carry more CO2 than oxygenated blood.

Question 27

What is the Henderson-Hasselbalch equation?

Answer 27

pH= pK+ log10(A-/HA)

The relationship between blood pH, CO2 and HCO3- is described by the Henderson-Hasselbalch equation.

Question 28

What are the compensation systems?

Answer 28

Respiratory: blood pH regulates ventilation and so controls PCO2 (rapid response)

Renal: excretion of H+ in urine controlled by pH (slow response)

Question 29

What is acidosis?

Answer 29

Acidosis= blood pH too low

Question 30

What is alkalosis?

Answer 30

Alkalosis= blood pH too high

Question 31

If there is a problem with CO2 what would this be called?

Answer 31

Respiratory acidosis/alkalosis

Question 32

If there is a problem with bicarbonate what would this be called?

Answer 32

Metabolic acidosis/alkalosis

Question 33

Acid base abnormalities – alkalosis (pH >7.45), low CO2- what is it and why is it caused?

Answer 33

Respiratory alkalosis (low PCO2, normal HCO3-R too low- hyperventilating (anxiety, iatrogenic)
Iatrogenic- doctor caused

Question 34

Acid base abnormalities – alkalosis (pH >7.45), bicarbonate high- what is it what is it caused by?

Answer 34

Metabolic alkalosis (normal PCO2, high HCO3-)

Due to loss of H+ e.g. vomiting; abuse of antacid remedies

Question 35

Acid base abnormalities – acidosis (pH < 7.35), high CO2, high bicarbonate- what is it and what is it caused by?

Answer 35

Respiratory acidosis (high PCO2; high HCO3- = renal compensation)

Someone with COPD/chest infection (ventilatory failure)- CO2 is high

Question 36

Acid base abnormalities – acidosis (pH < 7.35), low bicarbonate- what is it and what is it caused by?

Answer 36

Metabolic acidosis (low HCO3-; low PCO2 = respiratory compensation)
Not enough bicarb- pH low

Patient is hyperventilating
Can be caused by renal failure; diabetic ketoacidosis; shock (poor tissue perfusion)
Tissues start to produced lactate, lactate build up = metabolic acidosis