Oxygen transport Flashcards
Why is haemoglobin critical to O2 transport?
-Oxygen has low solubility
-Hb enables O2 to be concentrated, hence increasing capacity and then released at respiring tissues
What are the 3 ways that oxygen content of blood measured/defined?
- O2 partial pressure, expressed as kPa
- Total O2 content(CaO2), expressed as mL of O2 per L of blood (ml/L)
- O2 saturation
What is O2 partial pressure?
the partial pressure of O2 within a gas phase (at a gas-liquid
interface) that would yield this much O2 in the plasma at equilibrium”
What is the total O2 content (CaO2)?
“the volume of O2 carried in each litre of blood, including O2
dissolved in the plasma and O2 bound to Hb”
What is the total O2 saturation?
the % of total available haemoglobin binding sites that are occupied
by oxygen
What does the gradient of the oxygen-haemoglobin dissociation curve mean?
It means the cooperative binding of O2 to Hb
What does the plateau mean in the oxygen-haemoglobin dissociation curve?
It means the saturation of O2 binding sites
Why is hemoglobin so effective at transporting oxygen within the body?
The structure of Hb produces high O2 affinity, therefore a high level
of Hb-O2 binding (and saturation) is achieved at relatively low PO2.
What does the oxygen-haemoglobin binding curve shift to in order to provide effective transport of oxygen?
The oxygen-haemoglobin binding curve
shifts to offload oxygen to demanding tissues
What does a leftward shift of the oxygen-haemoglobin binding curve mean?
-Higher Hb-O2 affinity therefore Hb binds more O2 at a given PO2
What does a rightwards shift of the oxygen-haemoglobin binding curve mean?
-Lower Hb-O2 affinity therefore Hb binds less O2 at a given PO2
What is the bohr effect?
Effect of CO2 & pH on Hb-O2
affinity
What happens in a leftward shift to CO2, pH, 2,3 DPG and temperature?
-Decreased CO2
-Increased pH(alkalosis)
-Decreased 2,3 DPG
-Decreased temperature
What happens in a rightward shift to CO2, pH, 2,3 DPG and temperature?
-Increased CO2
-Decreased pH(acidosis)
-Increased 2,3 DPG
-Increased temperature
When does O2 affinity change and what does this enable?
Hb O2 affinity changes depending on the local
environment, enabling O2 delivery to be coupled to demand
How is O2 affinity like in lungs?
-Increased PO2
-Decreased PCO2
-Increased pH
therefore increased O2 saturation
How is O2 affinity like in resting tissue?
-Decreased PO2
therefore decreased O2 saturation and O2 moves from Hb to tissue
How is O2 affinity like in working tissue?
-Decreased PO2
-Anaerobic respiration and hypoxia produce lactic acid(H+), CO2 and 2,3 DPG
-Therefore O2 demand increases, CO2 increases, pH decreases and 2,3 DPG increases
-This means that Hb-O2 affinity and binding decreases
-Therefore O2 saturation decreases and there’s an increase in O2 movement from Hb to tissue
What does oxyhaemoglobin appear as?
Appears as red
What does deoxyhemoglobin appear as?
Blue
What is cyanosis?
purple discoloration of the skin
and tissue that occurs when the
[deoxyhaemoglobin] becomes excessive.
What are the symptoms of central cyanosis?
Bluish discoloration of core, mucous
membranes and extremities
What causes central cyanosis?
Inadequate oxygenation of blood
E.g. hypoventilation, V/Q mismatch
What are the symptoms of peripheral cyanosis?
Bluish coloration confined to
extremities (e.g. fingers)
What are the causes of peropheral cyanosis?
Inadequate O2 supply to extremities
* E.g. small vessel circulation issues
What are the causes of anaemia?
-Iron deficiency(decreases production)
-Haemorrhage(increases loss)
HB Affinity comparison of CO and O2
Hb has >200x affinity for carbon monoxide (CO) than O2 and
competes for the same binding site.
What happens in carbon monoxide poisoning?
-Increased CO-Hb
-therefore decreased O2 capacity
What pigmentation does carboxyhemoglobin have and hence when does hypoxia occur?
Carboxyhaemoglobin has cherry red pigmentation, hence hypoxia
occurs in the absence of cyanosis
What are the clinical aspects of Hb and O2 transport in anaemia ?
-Decreased O2 content
-Normal saturation
-Normal PaO2(the same amount is dissolved in the plasma)
-Decreased concentration of Hb and decreased concentration of O2-Hb
What are the clinical aspects of Hb and O2 transport in carbon monoxide poisoning?
-CO inhibits glycolysis in RBCs, hence decreases DPG
-This shifts curve to the left and this decreases unloading
