3.3 Oxygen in the Blood Flashcards
How do you work out concentration of dissolved oxygen?
[O2]dissolved = Solubility x pO2
What is average cardiac output?
5L/min
What are the two oxygen binding pigments?
Haemoglobin
Myoglobin
Where is Hb found and how much oxygen can it bind?
Present in the blood
Tetramer - Binds 4 O2
Where can myoglobin be found and how much oxygen can it bind?
Present in muscle cells
Monomer - Binds 1 oxygen
What does the myoglobin dissociation curve look like?
Rectangular hyperbola
Why do we express saturation as a percentage in dissociation curves?
Because binding is saturated above a given pO2
The amount of O2 bounds depends on the amount of pigment when not using a percentage
Percentage is independent of pigment concentration
What are the two states of Hb?
Low affinity T state
- Difficult for oxygen to bind
High affinity R state
- Easier for oxygen to bind
Which state is Hb in at low PO2?
Tensestate
Hard for the first O2 molecule to bind
What shape is the Hb dissociation curve?
Sigmoidal
At what O2 KPa is Hb saturated?
Above 9-10kPa
At what oxygen kPa is Hb unsaturated?
1kPa
At what oxygen kPa is Hb half saturated?
3.5-4kPa
What is the oxygen content in arterial blood leaving the lungs?
8.8mmol/L
Normal Hb content = 2.2mmol/L
Each Hb molecule can bind 4 oxygen molecules
2.2 x 4 = 8.8mmol/L
What is the amount of oxygen given up in the tissues?
3mmol/L
Metabolically active tissue - pO2 = 5kPa
So Hb saturation drops to 65%
So 35% of oxygen is given up
8.8 x 0.35 = 3 mmol/L
How low can tissue pO2 get?
Most tissues 3kPa
Can be lower in metabolically active tissues where there is a higher capillary density (because it doesn’t have as far to diffuse)
Briefly describe the Bohr shift
pH affects the affinity of Hb
Acidic conditions - shift to right - promotes T state - harder for oxygen to bind
Alkaline conditions - promotes R state
What happens to oxygen in metabolically active tissues and why?
Given up
- Lower pH
- Increased temperature
Why is improved extraction of oxygen by the tissues needed during extreme exercise?
Extreme exercise can increase metabolism by 10x but cardiac output only increased by 5x
What is the normal RBC level of 2,3-BPG?
5mM
Under what conditions may 2,3-BPG increase?
Anaemia
Altitude
What affect does increased 2,3-BPG have on the dissociation curve?
Shifts to the right
Allows more oxygen to be given up in the tissues
At what level in the blood is HbCO fatal?
> 50%
Define hypoxemia
Low pO2 in arterial blood
