Gas pressures and haemoglobin

Question 1

what does 1kPa equal?

Answer 1

7.5mmhg or 1000N/m2

Question 2

What does Dalton’s law state?

Answer 2

Dalton’s law states that the total pressure is equal to the sum of the component partial pressures.

Question 3

what is atmospheric pressure?

Answer 3

~100kPa

Question 4

what is PO2?

Answer 4

21kPa

Question 5

the partial pressure of a gas in solution is equal to

Answer 5

that in gaseous form at equilibrium

Question 6

what does Henry’s law describe?

Answer 6

the solubility of a gas.

Question 7

[gas] =

Answer 7

partial pressure x solubility coefficient

Question 8

state the normal Po2, hb saturation and O2 content of mixed and arterial blood.

Answer 8

arterial blood:
PO2= 13.3kPa
97-98% Hb saturation
200ml/l O2 content

Mixed blood:
PO2= 5.3kPa
75% Hb saturation
150ml/l of O2 content

Question 9

how much of the O2 is used per cycle?

Answer 9

1/3

Question 10

Oxygen is carried in what two forms?

Answer 10

dissolved in plasma and bound to haemoglobin

Question 11

O2 carried in which form is directly related to PaO2?

Answer 11

dissolved in plasma

Question 12

what are the normal range of Hb content of blood?

Answer 12

females: 11.5-16g/100ml
males: 13.5-18g/100ml

Question 13

what is the resting O2 consumption?

Answer 13

250ml/ min

Question 14

what is the role of haemoglobin?

Answer 14

haemoglobin allows efficient transport of high amount of O2 to meet demands at a normal cardiac output.

Question 15

how does O2 move from alveolar air to lung capillaries?

Answer 15

O2 diffuses down the partial pressure gradient (13.3 –> 5.3kPa)

Question 16

how is O2 delivered to tissues?

Answer 16

O2 diffuses from capillary to tissues which are using O2 and therefore have a lower PO2.

Question 17

Describe the structure of Hb

Answer 17

Haemoglobin is made of 4 subunits, each subunit consisting of a peptide globin chain and a haem group. each subunit will bind one molecule of O2

Question 18

1g of Hb will bind how much O2?

Answer 18

1.36ml

Question 19

what is average Hb concentration?

Answer 19

15g/100ml

Question 20

what is the normal O2 content?

Answer 20

200ml/ L

Question 21

describe the components of adult/ foetal and HbA2 haemoglobins?

Answer 21

HbA:
- 2 alpha chains and 2 beta chains
HbA2:
- 2 alpha chains and 2 delta chains
HbF:
- 2 alpha chains and 2 gamma chains

Question 22

when does the switch occur from embryonic haemoglobin to foetal haemoglobin?

Answer 22

13 weeks gestation

Question 23

what is the Hb concentrations of newborn?

Answer 23

80% HbF and 20%HbA

Question 24

when is the foetal Hb replaced by adult Hb?

Answer 24

at 3-6 months of age

Question 25

what are the commonest genetic disorders?

Answer 25

genetic defects in globin chains are the commonest of all genetic disorders

Question 26

what are the thalassaemias?

Answer 26

Thalassaemias are inherited disorders caused by defects in alpha or beta globin chain synthesis. this leads to imbalance of chains resulting in decreased synthesis of RBC and increased breakdown of mature RBCs. This impairs O2 carrying capacity. alpha thalassaemia is worse than beta thalassaemia as it is present in all forms of Hb.

Question 27

describe the cause and course of sickle cell disease.

Answer 27

sickle cell disease is caused by a point mutation in the beta chain. it is recessive- one copy of faulty gens –> HbAS = sickle cell trait, generally asymptomatic, anoxia manifesting in stress such as air travel, confers protection against malaria; 2 copies –> HbSS = sickle cell disease: symptoms variable from asymptomatic to death, increased turnover of cells can lead to severe haemolytic anaemia, severe pain due to vaso-occlusive crises and infarction.

HbS decreases the flexibility of the cell leading to a characteristic sickle shape. sickling leads to shortened erythrocyte survival and impaired flow through circulation.