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Semester 3 - Respiratory > Session 4 - Oxygen in blood > Flashcards

Session 4 - Oxygen in blood Flashcards

1
Q

How soluble is oxygen in water at 13.3 kPa?

A
  • Will dissolve 10%

* 0.13 mmol.l-1

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2
Q

What is the minimum oxygen we need per minute (in mmol)

A
  • 12 mmol

* Would require 92 litres of fluid- impossibly high

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3
Q

What problems do we encounter when faced with binding O2 to a solute?

A

• The reversibility of the reaction

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4
Q

Is the addition of O2 to haem a reduction reaction?

A

• No, it’s an oxygenation reaction

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5
Q

What is myoglobin?

A

• A haem storage unit found in muscle

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6
Q

What is a dissociation curve?

A
  • Plot of amount O2 bound vs pO2

* Total content then bound and dissolved

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7
Q

What happens at the top end of an oxygen dissociation curve?

A

• Chemical binding will saturate

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8
Q

How do you use a dissociation curve to work out how much oxygen taken in or given up?

A
  • Work out the difference in fractional saturations between the two pO2’s
    • Multiply by the amount bound at full saturation
    • Tells you how much O2 is taken or given up
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9
Q

What is the normal ppO2 in the lungs?

A

• 13.3 kPa

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10
Q

What is the normal ppO2 in the tissues?

A

• 5kPa

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11
Q

What is the structure of haemoglobin?

A
  • A tetramere
    • Each subunit has one haem + globin
    • Variable quaternary structure
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12
Q

What are the two states of haemoglobin?

A
  • Tense - strong relationships between subunits

* Relaxed - Weak relationships between subunits

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13
Q

How many O2 can one haemoglobin pick up?

A

• Four

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14
Q

In what state does haemoglobin pick up oxygen?

A

• Relaxed

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15
Q

Which oxygen does haemoglobin find it hardest to bind?

A

• The very first

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16
Q

What is sigmoidal binding, and why does this happen?

A
  • S shaped dissociation curve

* Easier to bind as oxygen content increases

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17
Q

When is haemoglobin saturated?

A

• Above 8.5/9 kPa

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18
Q

When is haemoglobin unsaturated?

A

• Below 1 kPa

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19
Q

What is half saturation point for haemoglobin?

A

• 3.5/4kPa

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20
Q

How does the dissociation binding curve for haemoglobin demonstrate reversibility?

A

• Saturation changes greatly over narrow range of pO2

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21
Q

What is the normal amount of O2 which should be bound to Hb leaving lungs?

A
  • 8.8 mmol/l

* 4 hb in each RBC, 2.2mmol per Hb

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22
Q

What is standard tissue kPa?

A

• 5 kPa

23
Q

What problems does the standard tissue kPa pose for Hb?

A

• Only removes 35% O2 from Hb

24
Q

How do tissues increase amount of O2 released from Hb?

A
  • Increase capillary density
    • Decrease pH
    • Increase temperature
25
Q

What is the state of Hb in acidic conditions?

A

• Tense

26
Q

How do cells utilise Hb’s tense state in acidic conditions?

A

• Metabolically active tissue release acid (H+), which shifts oxygen dissociation curve to the right

27
Q

If you can combine low pH and high temperature, what proportion of Hb loses O2?

A

• 70%

28
Q

What is the oxygen reserve?

A

• Only 27% O2 in arterial blood given up to tissues

29
Q

What three factors effect the haemoglobin dissociation curve?

A

• Increasing H+
• Increasing temperature
• Increasing CO2
○ Will shift to right

30
Q

What can you do if venous pO2 is known?

A

• A dissociation curve can be used to calculate the percentage of oxygen that has been given up to that tissue

31
Q

What are the three factors which determine gas exchange

A
  • Area available for the exchange
    • Resistance to diffusion
    • Gradient of partial pressure
32
Q

What can happen to CO2 in the blood?

A
  • Dissolved in blood
    • Reacts with water
    • Binds directly to proteins
33
Q

Why does Co2 dissolve in water?

A

• More soluble than O2

34
Q

Why does CO form when it binds directly to proteins?

A

• Carbamino compounds

35
Q

What does CO2 react with water to form?

A

• H+ and HCO3-

36
Q

What does the amount of CO2 reacting with water depend on?

A

• Amount reacting depends on concentrations of reactants and products

37
Q

What is the henderson hasselbach equation?

A

• pH = 6.1 + log (HCO3-/pCO2x0.23)

38
Q

What are two critical determinants of pH (other than H+)?

A
  • HCO3-

* CO2

39
Q

Outline the reaction of CO2 in an RBC

A
  • Reacts with water, forming HCO3- and H+
    • H+ removed by binding to RBC
    • Keeps reaction moving forward (CO2 + H20 -> H+ + HCO3-)
40
Q

What happens to HCO3- in RBC?

A
  • Released through RBC membrane

* Exchanged for CL

41
Q

How is HCO3- formed in plasma?

A

• Slow reaction between CO2 and water

42
Q

How is HCO3- formed in RBC/

A
  • Fast reaction between CO2 and water

* Due to the presence of HCO3-

43
Q

CO2 + H20 -> HCO3- + H+

In light of this equation, explain why HCO3- is rapid and constant in an RBC

A

• H+ consistently removed, favouring further HCO3- production

44
Q

How does Hb act as buffer in RBCs?

A

• H+ reacts with Hb, driving the reaction between CO2 + H20 (creating further H+ and HCO3-

45
Q

What do carbamino compounnds do?

A

• Bind directly to proteins, contributing to CO2 transport but not acid base balance

46
Q

Where is the concentration of carbamino compounds the greatest?

A

• More in venous blood, as pCO2 highest

47
Q

What is arterial blood Co2?

A

• 21.5 mmol/litre

48
Q

What is venous blood CO2?

A

• 23.5 mmol/litre

49
Q

What is the conc of HCO3- in arterial plasma?

A

• 25 mmol/l-1

50
Q

What happens to blood pH at higher concentration of CO2?

A

• pH will fall

51
Q

What is hydrogen carbonate in the blood derived from?

A

• Sodium hydrogen carbonate

52
Q

What is the purpose of having a high HCO3- in the plasma?

A

• Prevents CO2 reacting with water

53
Q

State the portions of CO2 travelling in particular forms

A
  • 80% as HCO3-
    • 11% as carbamino compounds
    • 8% travels as dissolved CO2

Semester 3 - Respiratory (18 decks)

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