Respiratory Physiology IV Flashcards
How does the oxygen partial pressure change as you move from air entering the main bronchi to the partial pressure of oxygen in the blood at the tissues?
It decreases considerably.
What does Henry’s Law state?
The amount of a given gas dissolved in a given type and volume of liquid (e.g. blood) at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid.
What happens to the concentration of gas in the liquid phase if the partial pressure in the gas phase is increased?
It increases proportionally.
What does the partial pressure of a gas in solution mean?
The partial pressure of a gas in solution is its partial pressure in the gas mixture with which it is in equilibrium.
What does Henry’s Law mean for the amount of oxygen dissolved in the blood?
It is proportional to the partial pressure of oxygen.
Is the amount of oxygen dissolved in blood alone enough to meet the resting oxygen consumption of our body?
No, only 1.5% of the total blood oxygen concentration is dissolved in the blood.
What is the value for normal oxygen concentration in arterial blood and what is the normal haemoglobin (Hb) concentration?
200 ml/L oxygen concentration.
150 g/L haemoglobin (Hb) concentration.
How do the percentages of oxygen carried bound to haemoglobin and in the dissolved form compare?
Bound to haemoglobin - 98.5%.
Dissolved in blood - 1.5%.
How many haem groups are in each haemoglobin molecule and how many oxygen molecules can each group bind?
Four haem groups per molecule.
Each can bind one molecule of oxygen.
When is haemoglobin considered fully saturated?
When all four haem groups are bound to a molecule of oxygen.
What is the primary factor which determines the percentage saturation of haemoglobin?
The partial pressure of oxygen.
Describe the structure of haemoglobin.
Four sub-units (haem groups): two beta and two alpha chains.
Each haem group contains an iron ion which binds to an oxygen molecule.
Describe the shape of the oxygen-haemoglobin dissociation curve.
“Sigmoid curve.”
Initial increase in % saturation is slow but then this increase gets greater.
Slowly begins to tail off to a plateau.
How does oxygen concentration of the blood change as haemoglobin concentration is changed? Why is this?
An increase in haemoglobin concentration results in a large increase in blood oxygen concentration.
A decrease in haemoglobin concentration results in a large decrease in blood oxygen concentration.
This is due to the majority of oxygen in the blood being bound to haemoglobin (98.5%) so its concentration has a great influence on oxygen concentration.
What is the formula to calculate the oxygen delivery index, DO2I?
DO2I = CaO2 x CI.
where CaO2 = oxygen content of arterial blood (ml/L);
CI = cardiac index (L/min/m^2).
What does the cardiac index do?
Relates the cardiac output to the surface area of the body (i.e. size of the individual).
(Normal range = 2.4 - 4.2 L/min/m^2.)
What is the formula to calculate the oxygen content of arterial blood, CAO2?
CaO2 = 1.34 x [Hb] x SaO2.
where 1.34 is the amount of oxygen in ml one gram of haemoglobin can carry when fully saturated;
[Hb] = haemoglobin concentration in gram/L;
SaO2 = %Hb saturated with oxygen.
What three factors can impair oxygen delivery to the tissues?
- Respiratory disease.
- Heart failure.
- Anaemia.
What two factors does the partial pressure of inspired oxygen depend upon?
- Total pressure (i.e. atmospheric pressure).
2. Proportion of oxygen in the gas mixture (~21% in the atmosphere).
Why does decreased partial pressure of inspired oxygen/respiratory disease reduce oxygen delivery to the tissues?
These can both decrease arterial PO2 and hence decrease Hb saturation with oxygen as well as dissolved oxygen in the blood.
Why does anaemia reduce oxygen delivery to the tissues?
Anaemia decreases the Hb concentration of the blood and hence decreases the oxygen content of the blood.
Why does heart failure reduce oxygen delivery to the tissues?
Heart failure decreases cardiac output.
What occurs when one oxygen binds to a haem group of a haemoglobin molecule? What significance does this have for the oxygen-haemoglobin dissociation curve?
The haemoglobin’s affinity for further oxygen binding increases.
The curve is therefore sigmoid as initially binding of oxygen is slower but then the affinity increases with more oxygen binding.
It also flattens as the partial pressure of oxygen further increases as all sites are becoming occupied.
What is the physiological significance of the flat upper portion of the oxygen-haemoglobin dissociation curve?
This means that a moderate fall in alveolar partial pressure of oxygen will not greatly diminish oxygen loading of haemoglobin.
What is the physiological significance of the steep lower part of the oxygen-haemoglobin dissociation curve?
This means that the peripheral tissues get a lot of oxygen for a small drop in capillary partial blood pressure.
What is the Bohr Effect?
A shift of the oxygen-haemoglobin binding curve to the right.
What three four changes cause the oxygen-haemoglobin curve to shift to the right?
- Increase in partial pressure of carbon dioxide.
- Increase in hydrogen ion concentration.
- Increase in temperature.
- Increase in 2,3-biphosphoglycerate (2,3-BPG).
What influence does the Bohr Effect have on oxygen delivery to tissues?
Increased release of oxygen by conditions at the tissues.
How does the structure of foetal haemoglobin (HbF) differ from adult haemoglobin in structure?
It has two alpha and two gamma (as opposed to beta) sub-units.
What does foetal haemoglobin (HbF) interact less with in red blood cells?
2,3-biphosphateglycerate (2,3-BPG).
What does the different structure of foetal haemoglobin (HbF) mean for its affinity for oxygen? What does this do to the oxygen-haemoglobin dissociation curve for HbF?
It increases its affinity for oxygen.
The curve is shifted to the left.
What advantage does the increased affinity of foetal haemoglobin (HbF) for oxygen give during foetal development?
It means that even if the partial pressure of oxygen in the mothers blood is low, it is still possible to transfer oxygen to the foetus.
Describe the shape of the myoglobin dissociation curve.
The myoglobin is shown on the graph to very quickly reach 100% saturation as partial pressure of oxygen increases initially, and quickly reaches a plateau.
“Hyperbolic curve”.
Why is the oxygen-myoglobin dissociation curve hyperbolic?
Only one molecule of oxygen binds to each molecule of myoglobin and so myoglobin becomes saturated quickly.
i.e. absence of the cooperativity seen in haemoglobin binding with oxygen.
Does myoglobin release oxygen when the partial pressure of oxygen is low or high?
(Very) low.
What is the purpose of myoglobin?
Provides a short term storage of oxygen for anaerobic conditions.
What does the presence of myoglobin in the blood indicate?
Muscle damage.
