Oxygen in Blood Flashcards
How many molecules of oxygen can Haemoglobin and Myoglobin bind and where is each one found?
Haemoglobin- 4 O2 molecules found in blood
Myoglobin- 1 O2 molecule bound, found in in muscle
Explain how amount of O2 bound relates to pO2 using the myoglobin dissociation curve
As pO2 increases, amount of O2 bound increases until the pigment is saturated
Therfore amount of O2 is dependent on amount of pigment
Why would you show the myoglobin dissociation curve as a % saturation?
% saturation shows binding independent of pigment concentration
What subunits make up Haemoglobin?
A tetramer of 2 alpha & 2 beta subunits
Each subunit has 1 haem and 1 globin
Explain the difference between ‘T’ and ‘R’ states of haemoglobin
-
‘T’= tense. Has a low affinity for O2
- O2 therefore difficult to bind
-
‘R’= relaxed. Has a high affinity for O2
- easier for O2 to bind
How does the state of Hb change dependent on pO2?
- low pO2 = Hb is ‘T’
- High pO2= Hb is ‘R’
How does O2 binding affect the state of Hb?
When no oxygen bound, Hb is T state
As more oxygen binds, the Hb becomes more ‘R’
Describe the shape of the Haemoglobin Dissociation Curve
Sigmoidal shape
As pO2 increases, % saturation quickly increases until saturated
What is the normal concentration of Hb? How does this relate the O2 content of blood?
2.2 mmol.l-1 Hb in blood
Each binds 4 O2
(2.2 x4) = 8.8 mmol.l-1 O2 in blood
How is O2 given up at metabolically active tissue?
Metabolically active tissue has pO2 ~5 kPa
At 5kPa, Hb saturation is 65% meaning 35% is given up at the tissues
In very metabolically active tissue pO2 drops even more → more O2 is given up
How does capillary density relate to pO2
pO2 can’t fall to below 3 kPa in most tissues
but in very metabolically active tissues a high capillary density means pO2 can afford to drop lower so more O2 is released
How does an acidic environment change the binding of O2 to Hb? In which direction would the curve shift?
Bohr-Shift - Curve shifts the the Right
Decrease in pH promotes ‘T’ state of Hb, Increase in pH promotes ‘R’ state of Hb
What is the effect of the Bohr Shift in metabolically active tissues?
Metabolically active tissues have lower pH
low pH promotes ‘T’ state so more O2 is given up to meet demand
How does temperature affect the oxygen dissociation curve?
How does this relate to metabolically active tissues?
Increased temperature shifts the curve to the right
Metabolically active tissues have a higher temperature so more O2 given up
What is the effect of an increase in 2,3 BPG on the O2 dissociation curve?
In what circumstances would BPG levels rise?
Increase 2,3 BPG shifts the curve to the right
BPG rises at altitude or in anaemia
How does Carbon monoxide poisoning affect Hb?
CO binds irreversibly with Hb to form COHb
Increased affinity of unaffected subunits for O2 ⇒ won’t give up O2 at tissues
Shape of curve no longer sigmoid
How does anaemia affect the shape of the O2 binding curve?
Curve is still sigmoidal and will give up O2 at tissues but is Hb lower so does not have as much O2 bound
What is the difference between Hypoxemia and Hypoxia?
Hypoxemia = low pO2 in arterial blood
Hypoxia = low O2 levels in body or tissues
What is cyanosis?
Bluish colouration due to unsaturated Hb
Distinguish between central and peripheral cyanosis
Central = around mouth, lips, mucous membranes due to poorly saturated blood in systemic circulation
- usually a cardiac defect/ lung problem
Peripheral= due to poor local circulation in hands and feet
What does pulse oximetry measure and how?
Oxygen saturation
Detects pulsatile areterial blood by red and infrared light
Why would pulse oximetry show normal % saturation even in an anaemic patient?
Doesn’t detect how much Hb is present
The Hb that is present will still be fully saturated so gives a normal reading
What does arterial blood gas analysis measure? How is it taken?
Total O2 content of blood
Arterial puncture from radial artery
