Gas Pressure

Question 1

What is a the partial pressure?

Answer 1

Relative pressure exerted by a component of a gas mixture based on the number of molecules

Question 2

What is the function of the upper airways?

Answer 2

Filtering
Warming
Humidifying
Distribution
Upper airways saturate the air and warm to body temperature
Partial pressure of H2O is dependent on temperature but not altitude and the human body is always at 37C

Question 3

What are the different conditions to measure gas mixture?

Answer 3

STPD- standard temperature, pressure, dry

BTPS- body temperature, pressure, saturated

Question 4

What is Boyle’s law?

Answer 4

At a constant temperature the pressure exerted by a constant number of particle is inversely proportional to the volume of the container
P=k.1/V

Question 5

Where can pressure be measured?

Answer 5

1. Outside chest wall Patm
2. Between pleural membranes Ppl
3. Inside alveoli P(A)
4. Inside the airways Paw
   Pressure are relative to atmospheric pressure
   Pressure differences/gradients are important

Question 6

Describe units of measuring pressure

Answer 6

1cmH2O= 0.75mmHg= 0.1kPa

Question 7

How is the majority of oxygen transported in the blood, and why?

Answer 7

Haemoglobin- 4 haem moieties
Alpha and beta globin chains will also bind CO2 and H on histadines residues
Beta chains also bind 2,3-DPG (diphosphoglycerate)
Carried discretely in RBCs
Plasma would have a much higher viscosity
Would be more open to degradation by enzymes and excretion by the kidneys

Question 8

Describe oxygen transport

Answer 8

Saturation (%)= O2 bound x 100/ O2 capacity
Sigmoid all shape of graph represents the cooperative binding of oxygen to haemoglobin due to allosteric changes- 1st and 4th oxygen is difficult to bind, 2nd and 3rd bind with ease
P50 is the partial pressure needed to achieve saturation
‘Plateau’ indicates that the lungs could almost half their partial pressure and still saturate the blood
Supplying oxygen to tissues ‘deoxygenates’ the blood but it is still ~75% saturated

Question 9

What can affect O2 transport?

Answer 9

The Bohr effect
Decreased affinity (right shift) results from an increase in:
PCO2
[H]
2,3-DPG
Temperature
All of these are found in metabolising tissues- help off-load oxygen from blood in to the tissue

Question 10

What does an increase in lung PO2 do to oxygen content in blood?

Answer 10

Haemoglobin remains saturated- 100%

The amount dissolved in the plasma increases do there is a slight incline to the ‘plateau’ as PO2 increases

Question 11

What is the O2 capacity of the blood?

Answer 11

Capacity= [Hb]x 1.39mlO2/g of Hb
=145g/L x 1.39= 202mlO2/L of blood
In equilibrium with the 2.4ml dissolved in the plasma
Content= Hb(A-V)+P(A-V)O2= 242+8= 250mlO2/min

Question 12

How is CO2 carried in the blood?

Answer 12

4% dissolved on the plasma
1% reacts with amino groups in proteins to form R-NHCOO- +H
5% dissolved in the cytoplasm of the RBCs
5% bound as deoxy-Hb-NHCOO-
Carbonic anhydrase in the RBCs forms H2CO2, from CO2 and H2O, which dissociates to form HCO3- and H- most of this is transported into the plasma coupled with the chloride shift to maintain neutrality
This reaction also happens spontaneously and slowly in the plasma
20% in RBCs
65% in the plasma

Question 13

What is that Haldane effect?

Answer 13

Initial rapid increase in CO2 as PCO2 increases
Still large changes seen in CO2 from arterioles to veins
CO2 carriage is non-saturable
Hypoxia increases Hb affinity for CO2 moving the curve up