Blood Gas Transport Flashcards
How is oxygen moved in the blood and in what proportions?
Dissolving in plasma (2%)
Binding to Hb (98%)
How is CO2 moved in the blood and in what proportions?
Dissolving in plasma (7%)
HCO3 (23%)
Bound to Hb (70%)
Why do the gases dissolve in plasma?
To get to the Hb
Are CO2 and O2 competitive for Hb?
No, bind to different binding sites
What are the three ways of measuring O2 content?
Partial pressure, total O2 content, O2 saturation
What is the unit of partial pressure?
KPa
What does the partial pressure measure?
O2 in plasma
What is the unit of total O2 conc?
Ml or L
What happens when the oxygen-haemoglobin curve shifts to the left?
Decreased CO2
Increased pH
Decreased 2,3-DPG
Decreased temp
What does it mean when the oxygen-haemoglobin curve shifts to the left?
Higher o2 affinity
Hb binds to more O2 at any given pO2
What happens when the oxygen-haemoglobin curve shifts to the right?
Increased CO2
Decreased pH
Increased 2,3-DPG
Increased temperature
What does it mean when the oxygen-haemoglobin curve shifts to the right?
Lower Hb-O2 affinity
Hb binds to less O2 at any given pO2
What enables O2 delivery to be coupled to demand?
The ability of HbO2 affinity to change
What is cyanosis?
Purple discolouration of skin and tissue that occurs when the deoxyhaemoglobin concentration becomes excessive
What is central cyanosis?
Bluish discolouration of core, mucous membranes and extremities
What causes central cyanosis?
Inadequate oxygenation of blood (hypoventilation, V/Q mismatch)
What is peripheral cyanosis?
Bluish colouration confined to extremities
Why does peripheral cyanosis happen?
Inadequate O2 supply to extremities (small vessel circulation issues)
Why would hypoxia occur, even if there is adequate ventilation and perfusion?
If the blood doesn’t carry enough O2 to meet tissue demands
What are the two causes of anaemia?
Iron deficiency (decreased production) Haemorrhage (increased blood loss)
How much more is COs affinity to Hb than O2?
> 200x
What colour is carboxyhaemoglobin?
Cherry red
What colour do people with CO poisoning go?
Bright red
What are the 7 signs of CO poisoning?
Headaches Nausea Dizziness Breathlessness Collapse Loss of consciousness Death
Why is more (%wise) CO2 carried in the plasma than O2?
CO2 has a higher solubility
What is the haldane effect?
Venous blood contains more CO2 than arterial blood
Why does venous blood have more CO2 than arterial blood?
Deoxyhaemoglobin has a higher affinity for CO2 and H+ than oxyHb does
What does increased oxyhaemoglobin mean for [CO2]?
Decreased CO2
What are the steps in the CO2 cycle?
1- CO2 is produced, dissolves in plasma and enters RBCs
2- CO2+H2O->H2CO3 (catalysed by carbonic anhydrase)
3- more CO2 can now diffuse into the RBC
4- H2CO3 -> HCO3- + H+. H+ gets stuck in RBC
5- H+ accumulation is prevented by deoxyHb acting as a buffer and binding to H+
6- increased [HCO3-] creates a diffusion gradient for it to leave the cell. It’s exchanged for Cl- to maintain electrical neutrality
What is the difference between the haldane and the Bohr effect?
Haldane- impact of O2 on CO2 transport
Bohr- impact of CO2 on O2 transport
How does the Bohr effect work?
Binding of CO2 to Hb induces a different structural change to Hb, which reduces Hb affinity for O2
What molecule transport is important in acid-base balance?
CO2
What can be diagnosed and interpreted from analysis of arterial blood gases and pH?
Signs of respiratory and metabolic distress
