Lecture 59 - Gas Exchange and Transport Flashcards
How much is 1 atm?
760 mmHg
Describe relative gas concentrations in the air
Nitrogen: high partial pressure
Oxygen: 160 mmHg
CO2: very low partial pressure
What is the difference between reidual and reserve volume?
Residual: can never be expirated
Reserve: amount that can be exhaled
Why have a residual volume?
- decreases energy required to reinflate lungs
- lung would not remain open
What happens to dead space during exercise?
nothing
Remains the same
Describe the features of the alveoli that make it good for gas exchange
- large surface area
- very thin wall to diffuse across
Describe the structures that oxygen moves across to get into the blood
One cell thick alveolar epithelium
Fused basement membrane
Endothelial cell
How does Fick’s law relate to alveolar structure?
Fick’s law of diffusion says;
- increased surface area
- decreased thickness
- greater pressure gradient
will lead to greater rate of diffusion of oxygen across the alveoli
Describe how concentration of gases in the atmosphere changes with altitude
The concentration does vary very much
It is the partial pressures of the gases that changes
Which variables can be altered to increase rate of diffusion of oxygen into the blood?
Concentration of oxygen in the breathed air
eg in Anaesthesia
65% oxygen in air
Describe what happens to the partial pressure of oxygen when air moves from the atmosphere into the alveoli
Why?
Partial pressure drops; 160 –> 100 mmHg
- mixing with old air with depleted oxygen
- air is moistened by mucous membrane
Compare the differences in PO2 in oxygenated and deoxygenated blood
Oxygenated: 100 mmHg
Deoxygenated: 40 mmHg
What happens to oxygen when we climb up higher than 5 km?
PO2 drops to 80 mmHg
Less oxygen is getting into the blood
Describe gases dissolving into liquids
When a liquid is exposed to a gas at a given pressure, the gas will move into solution until…
Partial pressure of gas is the same in the liquid and in the air.
How does solubility affect dissolution of gases into liquids?
Greater solubility:
- greater concentration of the gas in the liquid once equilibrium is reached
eg. CO2
Lesser solubility:
- lesser concentration of gas in the liquid once equilibrium is reached
eg O2
At equilibrium, will the concentration of the gas in the liquid and in the air be the same?
No
This depends on solubility of the gas
Is O2 or CO2 more soluble?
CO2
Describe how oxygen is transported in the blood
- O2 diffuses through cells into plasma
2. Combines chemically with haemoglobin (Hb)
Why must oxygen combine with Hb in the blood?
Because O2 is very insoluble
Hb increases the oxygen carrying capacity of the blood
How much Hb is present in the body?
Males: 15g / 100 ml
Females: 13g / 100 ml
What is the concentration of oxygen in the blood?
173 ml / L of blood
What is VO2 max?
The maximum amount of oxygen that can be taken up from the environment per unit time
What measurement is a good measure of fitness?
VO2 max
ie amount of oxygen that can be carried
How can VO2 max be increased?
EPO
Describe the O2-Hb dissociation curve
What does this mean?
Non-linear relationship between PO2 and binding
At alveoli:
considerable decrease in PO2, binding not much affected
At metabolically active cells:
- PO2 drops right down, binding decreases and O2 offloaded
What happens to O2 levels in the blood during exercise?
Drops to 25 mmHg
Describe the Bohr effect
Increase of O2 off-loading when needed
Under which conditions is increased off-loading of O2 seen?
- acidity
- increase in temperature
- high CO2
What is DPG?
What is its effect on Hb binding?
An intermediate of anaerobic metabolism
Di-phospho glycerate
Shifts the curve to the right –> increased O2 offloading
Under what conditions does DPG increase?
Hypoxia
Altitude
Anaemia
Describe the ways that oxygen is transported in the blood
1/ Bound to Hb
2/ Dissolved in the blood ( 1.5 %)
Describe how CO2 is transported in the blood
1/ in solution: 7%
2/ Bound to Hb: 23%
3/ As bicarbonate: 70%
What is the name for Hb carrying CO2?
Carbamino haemoglobin
Compare partial pressure of CO2 in alveoli and in blood
Aleoli: 40 mmHg
Blood: 46 mmHg
Describe the formation of bicarbonate
CO2 + H2O –> H2CO3 carbonic acid
under carbonic anhydrase (CA)
What is H2CO3?
Carbonic acid
Where is CO2 converted to carbonic acid?
In red blood cells
What happens after carbonic acid is formed by carbonic anhydrase?
Ionises to form bicarbonate
Is the carbonic anhydrase reaction favoured in the tissues?
Yes
Because there is much CO2 present because it is being made by the respiring cells
Describe what happens to bicarbonate in the lungs
Reaction is reversed
CO2 reforms
Diffuses out into the alveoli
When is carbamino Hb formation favoured?
Why?
When is carbamino Hb formation disfavoured?
At the tissues
Due to reduced Hb-oxygen affinity due to the Bohr effect
Carbamino Hb formation reversed at the lungs
(ie CO2 is kicked off)
What is the Haldane effect?
In low O2 environment, Hb has increased affinity for CO2
Compare grossly control of gas transport and control of respiration
Respiration: neurally controlled
Gas transport: passive
What are the effects of hyperventilation?
Why?
- increased ventilation
- decreased PCO2 in arteries
- increased PO2 in arteries
- decreased PCO2 in veins
- increased PO2 in veins
- increased alkalosis
- decreased respiratory drive
(more fresh air
Residual capacity being turned over more regularly
What is alkalosis?
Less carbonic acid in the blood
ie blood is more basic
What happens to PO2 in the arteries during hyperventilation?
Increases
What does decreased respiratory drive mean?
Breath can be held for longer
What happens to PCO2 in veins during hyperventilation?
Decreases
What are the effects of hypoventilation?
- Increased PCO2 in arteries
- Decreased PO2 in arteries
- Increased PCO2 in veins
- Decreased PO2 in veins
- increased acidosis
- increased respiratory drive
What is acidosis?
Increased carbonic acid in the blood
ie blood is more acidic
What happens to PO2 in arteries during moderate exercise?
Stays the same
Coming from the lungs, which is still oxygenating it to the same degree
What happens to PO2 in veins during moderate exercise?
Decreases
- Muscles consuming more
- increased ventilation
Which process does PCO2 control?
Ventilation
