Session 3- Oxygen in blood and tissues Flashcards
R state
High affinity for oxygen in R state - easier for oxygen to bind
T state
Low affinity for oxygen in T state - difficult for oxygen to bind
when Hb is at the tissues so o2 is more likely to be released and given up to the metabolically active tissues
Cooperativity
As each o2 binds the molecule becomes more relaxed ad binding of the next o2 molecule is easier
Why does gas pressure change when it enters our upper respiratory tract
It is humidified with water vapour
What is the partial pressure of oxygen in the URT vs alveoli
URT- pO2 = 19.8 kPa
Alveoli =13,3 kPa
Why is there a difference between the partial pressure of oxygen in the URT vs alveoli
When we breath we do not completely replace all teh air in our lungs
Older air has had o2 continually extracted and CO2 constantly being added
Hence percentage o2 less in alveolar air, hence pAo2 is lower than in URT and pAco2 high
PAco2 vs paCo2
A- alveoli a- arterial bloo
When gases are dissolved in body fluids when is equilibrium reached
Rate of gas entering liquid = rate of gas leaving the water
The partial pressure of the gas in the liquid = partial pressure of the has in the air above it
What does pO2 reflect
The amount of dissolved O2 in the blood not including Hb bound oxygen
Factors affecting rate of diffusion
The solubility of the gas in teh liquid; greater the solubility, faster the rate of diffusion
Molecular weight if the gas
-higher the molecular weight slower the rate of diffusion
What is the diffusion coefficient used to determine
The relative rates at which different gases will diffuse acros the same membrane at th same pressures
Which diffuses faster and why between CO2 and o2
CO2 much mire soluble than o2- so diffuses faster than o2
Molecular weight of CO2 is larger than o2
However co2 is faster
Why is o2 gas exchange more impaired in diseased lungs
In diseased lung with lower alveolar o2 partial pressure, there is a less partial pressure gradient. O2 gas exchange more impaired tha co2 because of o2 being less soluble
What is the diffusion barrier room alveolar air to RBC
Fluid film lining alveolus Epithelial cell of alveolus Interstitial space Endothelial cell of capillary Plasma Red cell membrane
Factors affecting rate of gas diffusion- disease examples
Thickness of the membrane
-increase as a result of oedema fluid in the interstial. Space and in alveoli
Surface area of the membrane
-emphysema
What changes in diseases with impaired diffusion
- co2 always diffuses much faster tha o2
- so diffusion of o2 affected -> pO2 is low
- difffusoon of co2 not affected -> pCo2 normal
What happens when PAO2 is low
Hypoxia vasoconstriction of pulmonary arterioles occurs
-this diverts blood to between ventilated alveoli
What is hypoxaemia
Low partial pressure oxygen in arterial blood
Why cant over-ventilated alveol compensate for under-ventilated alveoli
98% of our oxygen carried on Haemoglobin
2% oxygen content is dissolved oxygen
Haemoglobin is already carrying all that it can carry - it is saturated
What is decompression sickness in divers
Nitrogen moved from high pressure in the lungs into the blood- low pressure
A slow return to the surface lets the nitrogen rein to the lungs where it is breathed out
Swimming up too quickly doesnt give the nitrogen enough time to leave the blood - instead it can form painful bubbles
When does optimal gas exchange occur
When ventilation and perfusion are matched at the alveolar capillary level
R state
High affinity for oxygen in R state -easier for oxygen to bind
What is cooperativity
When the partial pressure is low Hb is tense so ut is ahead for the first o2 molecule to bind
As each o2 binds the molecule becomes more relaxed and binding of the next o2 molecule is easier
What is alveolar pO2
13.3 kPa
How do we calculate the total content of O2 in the blood
1) partial pressure of o2 in arterial blood x solubility Coe-efficient of oxygen in plasma which is 0.01mmol/L/kPa X 13.5Kpa = 0.135mmol/L
Then we add the amount attached to haemoglobin
2.2mmol/L - normal Hb conc
4 Hb on each Hb
4x 2.2 =8.8 mmol/L
Total = 0.135 + 8.8mmol/L
How do we measure adequacy of oxygenation
Oxygen saturation - Sats
Arterial blood gas- ABG
What is alveolar pCo2
5.3Kpa
What does increasing the pO2 in our lungs to more than 13.3kPa do to the total content of oxygen in the blood
Nothing because the oxygen content is primarily determined by the o2 carried on haemoglobin and it is sarated at 13.3kpa
What increases Hb unloading
Bohr shift
Increases in temp
Drop in pH
Increases in 2,3 DPG
What is teh total amount of oxygen in the blood determined by
The oxygen bound to haemoglobin and the amount of oxygen and the amount of oxygen dissolved in the blood which is low because oxygen has a low solubility in blood
What is the arterial partial pressure of oxygen determined by
Function of the amount of dissolved oxygen which depends on the alveolar pO2 not the amount of o2 on Hb
Why does someone with anaemia have a normal arterial partial pressure of oxygen
Oxygen bound to Hb does not contribute to arterial partial pressure as it is no longer a free gas but rather chemically bound
What is the partial pressure of oxygen in venous blood
5.3-6kpa
How low can tissue pO2 get
Cannot fall below 3Kpa
What is teh effect on CO in the O2 dissociation curve
Causes a leftward shift in oxy-haemoglobin
Reduced o2 release
Signs of carbon monoxide poisoning
Headache Nausea Vomiting Slurred speech Confusion
What is hypoxaemia
Low partial pressure of oxygen in arterial blood
What is hypoxia
Low oxygen levels relative to need in body or tissues
What is cyanosis
Bluish colouration due to unsaturated b
Deoxygenated Hb is less red than oxygenated Hb
What effect does elevated temp have on O2 curve
Shifts to the right - ,more easily released
Lower pH on curve
Acidosis - shift to right
What is p 50
the partial pressure of oxygen necessary to bind
50% of available haemoglobin
