Gas Exchange Flashcards
What is Daltons’s law?
partial pressure of a gas mixture is equal to the sum of the partial pressures of the gas in the mixture
What is Fick’s law?
diffusion rate is proportional to the concentration gradient* the exchange surface area * the diffusion capacity of the gas / the thickness of the exchange surface
What is Henry’s law?
At a constant temp, amount of a gas that dissolves in a particular type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
What is Boyle’s Law?
At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas
What is Charles’ law?
At a constant temperature, the volume of gas is directly proportional to temperature of that gas
What are the % of nitrogen, oxygen, argon and carbon dioxide in air?
N - 78.09%
O - 20.95%
A - 0.93%
C - 0.04%
How does the composition of air differ between room air and high altitude air?
No difference, just the relative volumes are smaller in high altitudes in atmosphere
As air is breathed in and it reaches the alveoli, what 3 things change?
The air is warmed, humidified and slowed (protects the lungs)
Compare the partial pressures of O2, CO2 and H20 in dry air, conducting airways and respiratory airways.
dry air -
O2 = 21.3kPa
CO2+H20 = 0
Conducting airways -
O2 = 20
CO2 = 0
H20 = 6.3
Respiratory airways -
O2 = 13.5
CO2 = 5.3
H20 = 6.3
Explain how the the partial pressures of O2, CO2 and H20 differ in dry air, conducting airways and respiratory airways.
Oxygen highest in air, no C02 and H20. In conducting airways main change is water saturation. In respiratory airways, the O2 decreases, and C02 increases
Why can’t dissolved oxygen meet metabolic demands?
Only 16ml of oxygen will dissolve per min.
Oxygen consumption is 250ml/min.
Hb is allosteric, what does this mean?
It changes shape depending on what binds or doesn’t bind to it
When oxygen binds to Hb which changes occur?
Conformational change so the structure relaxes and greater affinity for oxygen. The middle area changes too - becomes a binding site for 2,3 - DPG
If more ATP is being made, what is happening to 2,3 - DPG production?
Increasing as it is a product of glycolysis
What does 2,3 - DPG do?
It binds to Hb and squeezes oxygen out so more is used by tissues. It decreases the affinity for oxygen so more unloading occurs.
What is cooperativity of Hb?
The changing of its shape and affinity depending on the amount of bound oxygen
What is methaemoglobin?
Fe2+ gets oxidised to Fe3+ and this cannot bind oxygen. Causes functional anaemia. Nitrites can cause MetHb formation
Why is it beneficial that the oxygen dissociation curve is sigmoidal and not linear?
If it was linear, then there would be a large variation in oxygen loading in the lungs (might not get max) and very little unloading in tissue (not max efficiency. As it is sigmoidal, you get 100% saturation in lungs across a range of pO2 and in tissues, the saturation can go decrease a lot so lots of unloading
What does p50 tell us?
The partial pressure of oxygen where 50% of haemoglobin is saturated. Find it by drawing a line at 50% saturation.
What factor shifts the ODC to the right?
Increase in energy consumption - exercise
Which changes occur during exercise?
- increase in temp
- acidoisis
- hypercapnia (high co2)
- increase in 2,3 - DPG
Which things cause the ODC to shift to the left?
- decrease in temp
- alkalosis
- hypocapnia
- decrease in 2,3 - DPG
What does carbon monoxide poisoning do to the ODC?
Curve shifts downwards and left
Why does carbon monoxide shift the ODC the way it does?
- Hb has greater affinity for CO
- It binds to Hb and reduces amount of O2
- Those O2 molecules binding to Hb are bound more tightly and less likely to unload
- The overall effect is that the is an increase in affinity but decreased capacity to bind O2
In an anaemic person what happens to the ODC?
It moves down, as the Hb conc is lower but saturation of the Hb is the same
What does polycythaemia do to the ODC?
Curve shifts up. Polycythaemia is when the haematocrit is higher due to more RBCs. This leads to more oxygen carrying capacity so blood flows slower, reducing oxygen delivery
Why is pulse oximetry not useful alone?
It tells us the saturation of Hb but not the amount of Hb so both should be used together
Where do foetuses get oxygen?
From the placenta - they take oxygen as they have higher affinity
What does the oxygen dissociation curve for myoglobin look like?
It is hyperbolic. It isn’t Hb but it is a monomeric protein in muscle that keeps oxygen for later.
What is the type of blood arriving at the alveoli?
It is mixed venous blood not deoxygenated as it contains 75% oxygen - around 5.3 kPa
How does oxygen move from the alveoli to the red cell?
Higher pressure in the alvelous so oxygen dissolves into the blood and due to the concentration being higher than the pressure in the cell, it diffuses in. Hb is 100% concentrated
When the blood arrives at the tissue what is its saturation and why?
It is around 97% because the blood is diluted by bronchial circulation which supplies the lungs with blood to survive. This blood trains into the pulmonary circulation before returning to the left atrium
What happens to oxygen concentration and saturation in the tissues?
from 20 to 15 mL/dL
97 - 75%
What is oxygen flux?
The overall amount of oxygen being deposited in tissues - around 5mL/dL
What is a normal CO?
5 L/min
What happens to carbon dioxide once it dissolves in the blood?
Carbon dioxide is more soluble than oxygen so once in blood can form carbonic acid after meeting water - this can dissociate into proton and bicarbonate (very slow)
What happens to carbon dioxide inside of RBC and how does it compare to what happens in the plasma?
CO2 can move into RBC where enzymes are (carbonic anhydrase) so then bicarbonate is made at a faster rate than in plasma
How is the homeostasis of water maintained inside the RBC?
Inside the RBC, the carbonic acid dissociates into bicarbonate and proton so the bicarbonate diffuses into plasma via AE1 protein and Cl- enters (maintains equilibrium anion in for anion out). Cl- moving in draws in water. This prevents cell drying as water was being used to make bicarbonate
Where does carbon dioxide bind in Hb?
Carbon dioxide can bind to the amine end of a globin chain in Hb making carbaminohaemoglobin
What happens if the H+ concentration in the RBC increases, and how is it dealt with?
If H+ conc is high in the red cell, pH will decrease. This is solved by Hb - the residues on globin chains accept H+ acting as a buffer.
What is the flux of CO2 in venous and arterial blood?
What is the difference in CO2 conc between venous and arterial blood?
How much CO2 is made per minute?
CO2 flux changes from 52 to 48 (venous TO arterial)
There is a 4mL/dL increase in CO2 conc in venous blood
200mL of CO2 made a min
Is oxygen consumption equal to carbon dioxide production?
No, as water is lost in metabolism
What is pulmonary transit time?
Amount of time that blood is in contact with respiratory surface - around 0.75 s
How long does exchange take to occur?
Exchange occurs in 0.25 s
What can cause exercise induced hypoxia?
Cardiac output is higher and pulmonary blood flow increases so the time taken for oxygen to diffuse is longer
Does CO2 or O2 diffuse faster and why?
CO2 diffuses faster than O2 as it is more soluble
Why is blood flow to the whole lung not uniform? What does the bottom of the lung get more of?
Blood flow to lung is not the same because of gravity. Bottom of lung gets more perfusion and ventilation - less resistance
How do the V/Q ratios differ in the base and apex?
In the base, the V/Q ratio tends towards 0 but towards infinity in apex (V/Q is ventilation perfusion)
Where the lines for V and Q cross, what is the significance?
Ventilation is equal to perfusion
How do the 3 zones of the lung differ in the alveolar, arterial and venous pressure?
Zone 1 (apex) - alveolar pressure>arterial>venous
Zone 2 (middle) - arterial>alveolar>venous
Zone 3 (base) - arterial>venous>alveolar
(arterial always greater than venous or blood flows back)
What is the Haldane effect (CO2 dissociation curve)?
Hb binding to oxygen allows more unloading of CO2 in lungs. When Hb is 100% saturated with O2 no CO2 bind and opposite at 75% saturation. Deoxyhaemoglobin binds CO2 and protons more readily
