Carriage of O2 and CO2 in the Blood

Question 1

What are the 2 main ways in which oxygen is carried in the blood?

Answer 1

Dissolved in the blood or combined with haemoglobin

Question 2

What equation is used to determine the amount of oxygen that dissolves in the blood?

Answer 2

volume of oxygen = 0.0232 x pO2

0.29 = 0.0232 x 12.5

By the time the oxygen reaches the alveoli, the pO2 is 12.5 kPa

Question 3

What equation is used to determine partial pressure?

Answer 3

partial pressure = fractional concentration x barometric pressure

Question 4

What is barometric pressure in the atmosphere?

Answer 4

101.3 kPa

Question 5

How much oxygen is dissolved in one decilitre of blood?

Answer 5

0.29 ml of oxygen is dissolved in each 100 ml of blood

Question 6

In cold water, how does the amount of gas dissolved differ than at 37 degrees?

Answer 6

There is more oxygen and CO2 dissolved in cold water

More gas will dissolve at lower temperatures

Question 7

What is the significance of the value 0.0232 in the equation?

Is it a constant?

Answer 7

It describes the solubility of oxygen

Calculations are always at 37oC so it does not change

The value changes if the calculations are worked out at a different temperature

Question 8

What is oxygen saturation?

Answer 8

It describes how much of the haemoglobin in the blood is bound with oxygen, compared to how much haemoglobin there is in total

Question 9

How is oxygen saturation calculated?

Answer 9

Amount of oxyhaemoglobin divided by the total amount of haemoglobin

HbO2 / (HHb + HbO2)

Question 10

What do 
SO2
HbO2
HHb
stand for?

Answer 10

SO2 - oxygen saturation

HbO2 - oxyhaemoglobin

HHb - deoxyhaemoglobin

Question 11

What equation is used to determine how much oxygen is being carried by haemoglobin?

Answer 11

volume of O2 = SO2 x [Hb] x 1.39

19 = 0.97 x 14 x 1.39

Question 12

What is the Hüfner constant and what does it describe?

Answer 12

1.39

it describes the number of ml of oxygen that each gram of Hb can carry

Question 13

What is normal haemoglobin concentration?

Answer 13

14 grams per 100 ml

Question 14

How much oxygen is carried by Hb per 100 ml of blood?

Answer 14

Hb can carry 19 ml of oxygen per 100 ml of blood

Question 15

How many amino acids are in each of the 4 polypeptide chains that make up Hb?

Answer 15

141 - 146 amino acids per chain

Question 16

What is the tertiary structure of Hb?

Answer 16

A globular structure determined by the order of amino acids in the primary structure

It forms a crevice in which the haem group will sit

Question 17

What are the 2 forms in which Hb exists?

What does this describe?

Answer 17

Relaxed and tense forms

This describes how tightly packed the globin is within the chain

Question 18

What does Hb act/look like in the relaxed state?

Answer 18

The globin is more spread out

The crevices containing the haem group becomes slightly wider

The oxygen can access the haem group more easily

Question 19

What does Hb act/look like in the tense state?

Answer 19

The globin is more tightly condensed

The crevices become too small for the oxygen to fit into easily

Question 20

What happens upon binding of the first oxygen molecule to Hb?

Answer 20

As soon as one molecule of O2 binds to the haem group, the shape of the globin chain changes

This alters how tense the adjacent globin chains are

The globin chains relax a bit more with each O2 that binds

Question 21

Why does pO2 of the blood have to be high before Hb begins to be oxygenated?

Answer 21

The first molecule of oxygen does not bind to the Hb easily

Question 22

When deoxygenated blood returns to the heart, how saturated is the Hb and why?

Answer 22

Hb is still 75% oxygenated

As blood circulates around the body, only 25% of O2 that is bound to Hb is actually consumed

Question 23

Under normal circumstances, what part of the Hb molecule is used to carry oxygen?

Answer 23

Only the final binding site on each Hb molecule

This is the site that works the most efficiently

Question 24

What happens as partial pressure of oxygen becomes lower?

Answer 24

It becomes harder to carry oxygen in the blood

Question 25

What is meant by the term 'cooperativity'?

Answer 25

The way in which altering the state of one part of the protein affects the other components

Question 26

What causes the shape of the oxygen dissociation curve?

Answer 26

The cooperativity between polypeptide chains in the Hb molecule

Question 27

What happens at the bottom of the oxygen dissociation curve?

Answer 27

It is difficult to get the oxygen to bind to Hb The partial pressure must be increased significantly before oxygen starts to bind

Question 28

What happens at the top of the oxygen dissociation curve?

Answer 28

All of the oxygen binding sites are occupied and the curve levels off

Question 29

What does the arterial point on the oxygen dissociation curve show?

Answer 29

The saturation of normal arterial blood Saturation is around 97% and partial pressure of oxygen is 12.5 - 13 kPa

Question 30

What does the venous point on the oxygen dissociation curve show?

Answer 30

The saturation of normal venous blood Saturation is around 75% and pO2 is 6.3 kPa

Question 31

What is shown by P50 on the oxygen dissociation curve?

Answer 31

This is the point on the curve where Hb is 50% saturated pO2 is normally 3.5 kPa

Question 32

What is the P50 point on the oxygen dissociation curve used for?

Answer 32

To see whether a curve is normal or if it has been shifted

Question 33

What 3 factors can cause the oxygen dissociation curve to shift?

Answer 33

1. temperature 2. pH change (Bohr effect) 3. 2,3 diphosphoglycerate in the RBC

Question 34

What is 2,3 diphosphoglycerate and how is it produced?

Answer 34

It is produced by anaerobic metabolism It is a signalling mechanism to RBCs to show that there is not enough oxygen being delivered

Question 35

What happens as the oxygen dissociation curve shifts to the right?

Answer 35

The further to the right the curve moves, the more easily the Hb will give up oxygen It will be harder for Hb to take up oxygen in the lung

Question 36

What causes the oxygen dissociation curve to shift to the left?

Answer 36

increased pH decreased temperature decreased 2,3 DPG

Question 37

What causes the oxygen dissociation curve to shift to the right?

Answer 37

decreased pH increased temperature increased 2,3 DPG

Question 38

What are the 4 ways in which a Hb molecule may be abnormal?

Answer 38

1. absent globin chain 2. defective globin chain 3. defective iron atom 4. wrong ligand

Question 39

How can an abnormal Hb have an absent globin chain?

Answer 39

The globin chains may be absent from an individual's genes

Question 40

What causes thalassaemia?

Answer 40

The gene for one or more of the globin chains is very abnormal The gene is so abnormal that none on the globin chain is produced

Question 41

What causes alpha thalassaemia?

Answer 41

The alpha chain of Hb is not produced

Question 42

What is significant about alpha thalassaemia?

Answer 42

Both foetal and adult Hb contain alpha subunits The foetus often dies before it reaches full development

Question 43

What is the consequence of beta thalassaemia?

Answer 43

It is less severe than alpha Patients will keep foetal Hb for their whole life

Question 44

What causes sickle cell disease?

Answer 44

A single amino acid substitution on the beta globin chain which interferes with the interactions of this globin chain with the other subunits

Question 45

What happens when Hb becomes deoxygenated in sickle cell disease?

Answer 45

The Hb molecules in the RBCs begin to stick together This changes the shape of the RBC

Question 46

When does sickling occur in sickle cell disease? What is significant about this?

Answer 46

At low pO2 this is usually when patients develop infections, become hypoxic or cold

Question 47

How may an iron atom become defective in Hb?

Answer 47

Fe2+ is oxidised to Fe3+ which does not carry oxygen

Question 48

What happens when Hb contains Fe3+? What % of Hb in the blood has Fe3+ instead of Fe2+?

Answer 48

This creates methaemoglobin which doesn't carry oxygen 0.5%

Question 49

How is methaemoglobin usually produced?

Answer 49

Usually drug-induced Drugs used to treat leprosy, local anaesthetics

Question 50

How many times more strongly does CO bind to Hb compared to O2?

Answer 50

CO binds to Hb 250 times more strongly than oxygen

Question 51

What happens when CO binds to Hb instead of oxygen?

Answer 51

The Hb carrying CO is no longer available to carry oxygen

Question 52

What are the main sources of carbon monoxide?

Answer 52

Smoking and house fires

Question 53

What is a buffer?

Answer 53

A solution that can minimise changes in the free H+ concentration and therefore in pH

Question 54

How is pH calculated?

Answer 54

pH = -log [H+]

Question 55

What does a buffer consist of?

Answer 55

A weak acid and its base in equilibrium

Question 56

What is the general buffer equation and the equation for carbonic acid?

Answer 56

acid H+ + base H2CO3 H+ + HCO3

Question 57

What happens if H+ ions are added and removed to the buffer system?

Answer 57

When H+ is added, the equation shifts to the left to remove some of the added ions When H+ is removed, the equation shifts to the right as some acid dissociates to increase H+ concentration

Question 58

What is the role of a buffer?

Answer 58

It minimises changes in pH It does NOT correct the pH and make it normal

Question 59

What are the 4 buffer systems in extracellular fluid? What is their capacity (mmol H+ per L)?

Answer 59

bicarbonate - 18 plasma protein - 1.7 haemoglobin - 8 phosphate - 0.3

Question 60

What is the total buffering capacity of the blood?

Answer 60

28 mmol H+ per L

Question 61

How do proteins act as buffers?

Answer 61

They have carboxyl and amino groups at the end of a chain, which act as buffers They also have side chains which contain buffers

Question 62

What is the problem with proteins as buffers?

Answer 62

Protein molecules are large which means there are not many protein molecules in the blood

Question 63

How does Hb act as an effective buffer?

Answer 63

It has more side chains with buffering ability than any other protein

Question 64

What is the main buffer of intracellular fluid?

Answer 64

phosphate

Question 65

What are the limits of blood pH and what H+ concentration does this correspond to?

Answer 65

Blood pH is tightly controlled between 7.35 and 7.45 [H+] of 35 - 45 mmol/L

Question 66

Why must blood pH be tightly controlled?

Answer 66

Most biological functions depend on the activity of proteins The structure of proteins is very pH dependent

Question 67

What are the 3 ways in which CO2 can be carried in the blood?

Answer 67

1. dissolved in the blood 2. carbamino compounds 3. carbonic acid/bicarbonate

Question 68

What determines how much CO2 can dissolve directly in the blood?

Answer 68

It is dependent on the pCO2 of the blood and how soluble CO2 is at 37oC

Question 69

At 37oC, how much CO2 is dissolved in the blood?

Answer 69

3 ml CO2 dissolved per 100 ml of blood This is 10 x the amount of oxygen dissolved

Question 70

How does a carbamino compound form?

Answer 70

The carbon dioxide molecule is attached to an amino group on an amino acid

Question 71

Where are amino groups found within proteins?

Answer 71

The N-terminal group of all proteins and the side chains of lysine and arginine

Question 72

How does Hb form a carbamino compound?

Answer 72

Hb has lots of amino acids with NH2 side chains where CO2 can bind

Question 73

How much CO2 is carried in the blood in the form of carbamino compounds?

Answer 73

4 ml of CO2 per decilitre of blood

Question 74

How much carbon dioxide is carried in the blood in the form of bicarbonate ions?

Answer 74

45 ml of CO2 per decilitre of blood