1- Gas transport in the blood part 1

Question 1

what is effect of partial pressure on gas solubility?

Answer 1

according to henry’s law the amount of given gas dissolved is proportional to partial pressure of gas in equilibrium with liquid

= this means that if partial pressure of gas is increased then concentration of gas in the liquid (e.g. blood) is increased proportionally

Question 2

how many ml of oxygen is dissolved per litre of blood?

Answer 2

3ml O2 per litre at partial pressure oxygen 13.3 kPa (100 mmHg)

Question 3

how much oxygen is taken to tissues as dissolved oxygen under
a) resting conditions
b) strenuous exercise

Answer 3

a) (cardiac output 5L/min): 15 ml/min
b) (cardiac output of 30 L/min): 90 ml/min

Question 4

what is most oxygen in blood transported by?

Answer 4

by being bound to haemoglobin in red blood cells = 98.5 %
- only 1.5% carried in dissolved form

Question 5

how much oxygen is bound to haemoglobin?

Answer 5

haemoglobin molecule = 4 haem groups which each reversible bind to 1 O2 molecule
fully saturated = 4 O2

Question 6

what is the primary factor that determines the percent saturation of haemoglobin with O2?

Answer 6

oxygen partial pressure

Question 7

what is structure of haemoglobin?

Answer 7

4 haem groups with beta and alpha chains (2 of each)

Question 8

what is the relationship described by oxygen haemoglobin dissociation curve?

Answer 8

oxygen partial pressure increases as more haemoglobin bound =sigmoidal shape

• this indicates co-operactivity (more bound means more attractive for other O2 to come and bind)

*so saturation of haemoglobin dependant on partial pressure of oxygen (as also works opposite way, not much oxygen means less attractive for oxygen to go and bind)

Question 9

how do you calculate oxygen content of arterial blood (CaO2)?

Answer 9

1.34 x concentration of haemoglobin x %Hb saturated with oxygen (determined by oxygen partial pressure)

*1g of Hb carry 1.34 ml O2 when fully saturated

Question 10

when can oxygen delivery to tissues be impaired?

Answer 10

respiratory disease & decreased partial pressure of inspired oxygen = decrease arterial PO2 & hence decrease Hb saturation with O2 & O2 content in blood

heart failure = decreases CO

anaemia = decreases Hb hence decreases O2 content in blood

Question 11

what does partial pressure of inspired oxygen depend on?

Answer 11

atmospheric pressure (total pressure) and proportion of oxygen in gas mixture (about 21% in atmosphere)

Question 12

explain how the sigmoidal oxygen haemoglobin dissociation curve shows co-operactivity?

Answer 12

flat upper portions = moderate fall in alveolar PO2 but not enough to affect loading of haemoglobin (not enough people at party to make attractive)
steep lowering = crosses threshold at about 8 kPa where enough oxygen there and now bind so everyone wants to go and bind

Question 13

what is the bohr effect?

Answer 13

phenomenon where Hb saturation decreases as the following increase:
- partial pressure of CO2
- concentration of H+ (acidity)
- temperature
- 2,3-biphosphoglycerate

Question 14

what is different about fetal haemoglobin?

Answer 14

• differs in structure - 2 alpha and 2 gamma (instead of 2 alpha and 2 beta)
• hence interacts less with 2,3 - bisphosphoglycerate in RBC’s
• therefore have higher affinity for oxygen compared to adult haemoglobin means dissociation curve for HbF is shifted to left comparte to HbA
• means more saturation

*doesn’t have sigmoidal curve and not same co-operactivity so allows O2 to transfer from mother to foetus even if PO2 low

Question 15

where is myoglobin found?

Answer 15

skeletal & cardiac muscle not blood

Question 16

what is different about myoglobin and haemoglobin structure?

Answer 16

• only 1 haem group per molecule so no cooperative binding of O2
• dissociation curve hyperbolic not sigmoid
• myoglobin releases O2 at very low PO2
  (short term storage of O2 for anaerobic conditions)

Question 17

what does presence of myoglobin in blood mean?

Answer 17

muscle damage

Question 18

what contributes to off loading of O2 at tissues?

Answer 18

bohr effect = less saturation when high metabolism (acidic), high temperature, high carbon dioxide partial pressure and high 2,3-biphosphoglycerate

= this means oxygen unloaded at cells that are metabolising and also myoglobin at muscle cells (have higher affinity for O2)