Gas Transport Flashcards
How is oxygen carried in the blood?
Dissolved in plasma
Attached to haemoglobin
What is oxygen proportional do if its dissolved in plasma?
Partial pressure
if oxygen dissolves in plasma and its PO2 is 100mmHg, how much oxygen will there be?
0.3ml/100ml
What is formed when all four binding sites on haemoglobin have been filled?
Oxyhaemoglobin
Describe the oxygen-haemoglobin dissociation curve?
Sigmoidal
As one oxygen binds, it causes a conformational change making it easier for the next to bind
What happens if the partial pressure changes at the steep lower part of the oxygen dissociation curve?
Large amounts of oxygen can be extracted for a small drop in PO2
What happens if the partial pressure changes at the plateau at the upper end of the oxygen dissociation curve?
If PO2 falls, saturation is not greatly altered so at altitude the O2 supply is still usually adequate
How does PO2 change in the lungs after inspiration?
Goes from 40mmHg to 100mmHg so Hb essentially is fully saturates
How does PO2 change at the tissues?
PO2 has fallen by more than half, but the Hb is still around 75% saturated
What things shift haemoglobin saturation to the right?
Increase in;
Temperature
Hydrogen ions
CO2
2,3-bisphosphoglycerate
Why is an increase in temperature good?
Modifies haemoglobin structure so that it has less of an affinity for oxygen
This means warmed up muscles release O2 faster and a good reason to race-prep
How does an increase in CO2 move to Hb saturation curve to the right?
Increased CO2 leads to an increase in hydrogen ions which weaken the Hb-O2 interaction- called the Bohr Effect
When does the Hb saturation curve switch to the right?
At the lungs
What does the amount of oxygen carried in the blood equal?
Amount carried by haemoglobin + amount dissolved
How do you calculate amount carried by Hb?
Concentration in the blood multiplied by the maximum oxygen carrying capacity multipled by % saturation of Hb
How much haemoglobin is there in 100ml of blood?
15g
What is the total amount of oxygen carried in the blood?
20ml O2/100ml
Or 200ml of O2/litre
How can carbon dioxide be transported in the blood?
Dissolved in plasma
Bound to haemoglobin
As bicarbonate
How much of carbon dioxide is transported in plasma?
7-10%
How much of carbon dioxide is transported by haemoglobin?
10-20%
What does carbon dioxide bind to on haemoglobin molecule?
Amino acids
what is the Haldane effect?
Deoxygenation of Hb increases its ability to bind CO2 and vice versa in the lungs, oxygenation of Hb releases CO2 into plasma for transport into alveoli
What percentage of haemoglobin is found in bicarbonate form?
70-80%
what happens when CO2 dissolves in water?
Produces carbonic acid, this degrades quickly into hydrogen ion and bicarbonate
Bicarbonate diffuses down concentration gradient into plasma
hydrogen ions bind the haemoglobin
Chloride ions move into RBC to maintain electrical balance
Process reversed in the lungs, HCO3 moves back into RBC (chloride moves ut), reacts with H+ to form carbonic acid which is rapidly reacted by carbonic nhydrase to orm CO2 and water. CO2 diffuses into alveoli space.
What is the function of carbonic anhydrase?
Producing carbonic acid from CO2 and water
What is haemoglobin’s new name once CO2 binds?
Carbaminohaemoglobin
How do you calculate the pH of blood?
pK add the log( conc of bicarbonate/ conc of CO2)
What is the pK used to calculate the pH of blood?
6.1
What happens if ventilation decreases for too long?
CO2 increases
pH falls
Bicarbonate increases
Causing respiratory acidosis
What happens if the patient hyperventilates?
Patient blows off more CO2
pH rises
Levels of bicarbonate fall
Respiratory alkalosis
