Resp 3 - Gas Transport and Exchange

Question 1

What are the 5 gas laws?

Answer 1

1. Daltons Law- pp of gas mixture is equal to sum of all pp of the gases in the mixture
2. Ficks Law - diffusion proportional to (CG x SA X DC)/Thickness
3. Henrys Law - at constant temp, amount of gas that dissolves a given type and volume of liquid is directly proportional to pp of the gas in eqm with liquid. (bigger solubility coefficient = dissolves more easily)
4. Boyle’s Law - at constant temperature, volume inversely proportional to pressure
5. Charles’ Law - at constant pressure, volume directly proportional to temperature

Question 2

What happens as dry air passes down the respiratory tree?

Answer 2

The air gets warmed, humidified, slowed and mixed.

Question 3

Does methaemoglobin bind O2?

Answer 3

No - it can cause functional anaemia

Question 4

Why do we have a sigmoidal oxygen dissociation curve and not a linear one?

Answer 4

IF LINEAR:

1. Very little scope to increase unloading in tissues
2. Massive variation in oxygenation in the lungs

SIGMOIDAL:

1. Effectively 100% oxygenation in the lungs over a variety of Partial pressures.
2. Oxygen saturation in tissues can go from 76% to 8% - v high unloading capacity

Question 5

What is p50?

Answer 5

Partial pressure of oxygen when Hb is 50% saturated

Question 6

What is characteristic of the ODC shifting right? What changes take place?

Answer 6

Shifts to right when higher energy consumption occurs (e.g. exercise).

Changes:

1. Increased temperature
2. Acidosis
3. Hypercapnia (increased CO2)
4. Increased in 2,3 DPG

Question 7

What changes can be expected when the ODC shifts to the left?

Answer 7

1. Decrease in temperature
2. Alkalosis
3. Hypocapnia
4. Decrease in 2,3 DPG

Question 8

What does a downwards shifted ODC indicate?

Answer 8

It means that there is less oxygen, but the Hb saturation is still the same.

Could be anaemia (less Hb so lower O2 carrying capacity)

Question 9

What does an upward shifted ODC indicate?

Answer 9

Polycythaemia (increased packed cell volume in blood.

If Hct ratio increases, blood gets thicker and flows slower - impedes O2 delivery

Question 10

What does CO poisoning do the ODC?

Answer 10

It shifts the ODC downwards and to the left.

(i.e. increase affinity, decrease capacity).

CO binded to Hb also causes the Hb to hold more tightly onto the O2.

Question 11

Describe foetal Hb ODC.

Answer 11

It has a high affinity (needs to steal O2 from mothers blood).

It has a better p50 (50% HbO2 saturation achieved at a lower po2)

Question 12

Describe myoglobin ODC.

Answer 12

Monomeric protein with a hyperbolic ODC.

STEEPEST initial gradient then levels off v quickly.

It it needed for when muscle needs O2 rapidly

Question 13

Describe Oxygen transport at the alveolar surface.

Answer 13

1. Mixed venous blood arrives at exchange surface. It has a pO2 of 5.3 kPa.
2. Alveolus has a pO2 of 13.5 kPa, so O2 diffuses from exchange surface into blood.
3. Plasma O2 conc is higher than erythrocytic pO2, so O2 moves into RBC.

Question 14

Describe O2 transport at the tissues.

Answer 14

1. Blood reaching tissues is about 97% saturated (diluted by bronchial circulation - some O2 needed to keep lungs alive).
2. Following changes occur:
   O2 conc = 20.3 - 15.1 ml/dl
   O2 saturation = 97% - 75%
3. Oxygen flux = -5mL/dL
4. 50 dL in the body so 5 x 50 = 250 mL of O2 being consumed per minute.

Question 15

What is oxygen flux?

Answer 15

The overall amount of oxygen being deposited.

Question 16

Compare CO2 conversion into bicarbonate in plasma and in RBCs

Answer 16

1. CO2 in bloodstream is much more soluble than O2.
2. CO2 may react with water and form carbonic acid (H2CO3).
3. In plasma, Carbonic acid dissociates into a proton (H+) and bicarbonate (HCO3-). This is slow - no enzymes.
4. In RBC, Carbonic Anhydrase converts CO2 and H20 into carbonic acid, which then dissociates into H+ and HCO3-.

Question 17

Explain CO2 transport.

Answer 17

1. In RBC, carbonic acid dissociates into proton and bicarbonate.
2. Bicarbonate diffuses into plasma via AE1 transporter - Cl ion moves into RBC (maintains chemical electroneutrality). Cl movement into RBC is called Chloride shift
3. Water drawn into RBC due to Cl shift
4. CO2 binds to proteins also. CO2 binds to amine end of proteins - forms CARBAMINOHAEMOGLOBIN (HbCO2).
5. Excess protons mopped up - proteins make good buffers.
   e. g. negatively charged proteins make good proton acceptors (e.g. histidine).

Question 18

What happens to pH of RBC as it goes to the venous end?

Answer 18

pH decreases - becomes more acidic

Question 19

Describe the values of CO2 as RBC goes to venous end.

Answer 19

CO2 flux: +4mL/dL in CO2 conc

200 mL CO2 produced a minute

Question 20

O2 consumption is 250mL /min. CO2 production is 200mL /min. They aren’t equal. Why?

Answer 20

Some CO2 lost in metabolic water production.

Question 21

Name an allosteric property relating to CO2 binding.

Answer 21

Amount of CO2 binding to amine end of Hb protein depends on how much O2 is bound.

If O2 saturation is 100%, CO2 won’t bind to amine end. Hb becomes more receptive to binding CO2 at tissues.

Question 22

What is pulmonary transit time? What is it in humans?

Answer 22

The time during which gas exchange can occur between blood and alveoli

It is around 0.75s in humans.

When exercising, lines get stretched rightwards, but still enough time to reoxygenate blood.

Question 23

Which exchanges faster, O2 or CO2?

Answer 23

CO2.

Question 24

Describe ventilation perfusion matching/mismatching.

Answer 24

1. Less blood perfuses the apex of the lung - due to resistance of gravity
2. Better ventilation at bottom than at top.
   3.