Blood Gas Carriage (Session 4) Flashcards Preview

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Flashcards in Blood Gas Carriage (Session 4) Deck (53):
1

How soluble is oxygen in water at 13.3 kPa?

• Will dissolve 10% • 0.13 mmol.l-1

2

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

• 12 mmol • Would require 92 litres of fluid- impossibly high

3

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

• The reversibility of the reaction

4

Is the addition of O2 to haem a reduction reaction?

• No, it's an oxygenation reaction

5

What is myoglobin?

• A haem storage unit found in muscle

6

What is a dissociation curve?

• Plot of amount O2 bound vs pO2 • Total content then bound and dissolved

7

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

• Chemical binding will saturate

8

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

• 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

9

What is the normal ppO2 in the lungs?

• 13.3 kPa

10

What is the normal ppO2 in the tissues?

• 5kPa

11

What is the structure of haemoglobin?

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

12

What are the two states of haemoglobin?

• Tense - strong relationships between subunits • Relaxed - Weak relationships between subunits

13

How many O2 can one haemoglobin pick up?

• Four

14

In what state does haemoglobin pick up oxygen?

• Relaxed

15

Which oxygen does haemoglobin find it hardest to bind?

• The very first

16

What is sigmoidal binding, and why does this happen?

• S shaped dissociation curve • Easier to bind as oxygen content increases

17

When is haemoglobin saturated?

• Above 8.5/9 kPa

18

When is haemoglobin unsaturated?

• Below 1 kPa

19

What is half saturation point for haemoglobin?

• 3.5/4kPa

20

How does the dissociation binding curve for haemoglobin demonstrate reversibility?

• Saturation changes greatly over narrow range of pO2

21

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

• 8.8 mmol/l • 4 hb in each RBC, 2.2mmol per Hb

22

What is standard tissue kPa?

• 5 kPa

23

What problems does the standard tissue kPa pose for Hb?

• Only removes 35% O2 from Hb

24

How do tissues increase amount of O2 released from Hb?

• Increase capillary density • Decrease pH • Increase temperature

25

What is the state of Hb in acidic conditions?

• Tense

26

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

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

27

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

• 70%

28

What is the oxygen reserve?

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

29

What three factors effect the haemoglobin dissociation curve?

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

30

What can you do if venous pO2 is known?

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

31

What are the three factors which determine gas exchange

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

32

What can happen to CO2 in the blood?

• Dissolved in blood • Reacts with water • Binds directly to proteins

33

Why does Co2 dissolve in water?

• More soluble than O2

34

Why does CO form when it binds directly to proteins?

• Carbamino compounds

35

What does CO2 react with water to form?

• H+ and HCO3-

36

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

• Amount reacting depends on concentrations of reactants and products

37

What is the henderson hasselbach equation?

• pH = 6.1 + log (HCO3-/pCO2x0.23)

38

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

• HCO3- • CO2

39

Outline the reaction of CO2 in an RBC

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

40

What happens to HCO3- in RBC?

• Released through RBC membrane • Exchanged for CL

41

How is HCO3- formed in plasma?

• Slow reaction between CO2 and water

42

How is HCO3- formed in RBC/

• Fast reaction between CO2 and water • Due to the presence of HCO3-

43

CO2 + H20 -> HCO3- + H+
In light of this equation, explain why HCO3- production is rapid and constant in an RBC

• H+ consistently removed, favouring further HCO3- production

44

How does Hb act as buffer in RBCs?

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

45

What do carbamino compounnds do?

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

46

Where is the concentration of carbamino compounds the greatest?

• More in venous blood, as pCO2 highest

47

What is arterial blood Co2?

• 21.5 mmol/litre

48

What is venous blood CO2?

• 23.5 mmol/litre

49

What is the conc of HCO3- in arterial plasma?

• 25 mmol/l-1

50

What happens to blood pH at higher concentration of CO2?

• pH will fall

51

What is hydrogen carbonate in the blood derived from?

• Sodium hydrogen carbonate

52

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

• Prevents CO2 reacting with water

53

State the portions of CO2 travelling in particular forms

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