Lec 5 - Oxygen in the Blood Flashcards
What is the solubility factor of oxygen in water?
The solubility factor for O2= 0.01 mmol.l -1. kPa-1.
What is T state of haemoglobin?
Low affinity for oxygen in T state (tense)
—> In this state it is difficult for oxygen to bind.
What is R state of haemoglobin?
High affinity for oxygen in R state ( relaxed)
—> In this state it is easier for oxygen to bind.
When is haemoglobin in the T state?
it is in the T state when the partial pressure of Oxygen is low.
What is the oxygen content like in anaemic patients with good functioning lungs?
-If the patient’s lungs are functioning okay, but they are anaemic, the pO2 will be normal but the oxygen content will be lower because there is less Hb present.
What is the normal Hb concentration?
It is approx 2.2 mmol.l-1.
Link capillary density to pO2.
- The higher the capillary density, the lower the pO2 can fall.
- —> This is because it doesn’t have so far to diffuse.
- ——–> very metabolically active tissue will have a higher capillary density such as heart muscle.
What does the Bohr shift do?
- pH effects the affinity of haemoglobin.
- Acidic conditions shift the dissociation curve to the right, so lower affinity for O2 at higher pO2 values.
What state is promoted at different pH?
- low pH promotes T-state of Hb (tense state)
- High pH (alkaline) promotes R-state.
How does temperature in the tissues shift the dissociation curve?
- Increased temperature shifts it to the right.
- metabolically active tissues have slightly higher temperature so extra O2 is given up.
- This causes Hb to go into the tense state (T)
What is the maximum unloading of oxygen?
- Maximum unloading occurs in tissues where pO2 can fall to a low level.
- maximum unloading also happens in conditions where increased metabolic activity result in more acidic environment and higher temperature.
- under these conditions about 70% bound oxygen can be given up.
What does 2,3 - Bisphosphoglycerate do?
- 2,3-BPG levels increase with anaemia or at altitude.
- Increased 2,3-BPG shifts the Hb dissociation curve for O2 to the right.
- It allows more O2 to be given up to tissues because of shift in curve.
When does 2,3-BPG levels drop?
They drop in stored blood due to refrigeration.
- 2,3-BPG enzyme stops working and this limits how much O2 can be given up at tissues.
What does carbon monoxide poisoning do to Hb?
- Carbon monoxide reacts with Hb to form COHb.
- It increases the affinity of unaffected subunits for O2.
- Therefore won’t give up O2 at the tissues.
- Fatal if HbCO is greater than 50%.
What is hypoxemia?
This is when there is a low pO2 in arterial blood.
What is hypoxia?
This is when there a low oxygen levels in body or tissues.
What may cause hypoxia?
- Hypoxia may be because of peripheral arterial disease.
- –> The peripheral arteries are narrowed so there is reduced blood flow and you might get ischaemia because there is not enough blood.
- peripheral vasoconstriction can cause peripheral hypoxia.
What are some of the presentations of cyanosis?
- Bluish colouration due to unsaturated haemoglobin.
- Cyanosis can be peripheral (hands or feet) due to poor local circulation.
- —> or central (mouth, tongue, lips, mucous membranes) due to poorly unsaturated blood in systemic circulation.
What can be used to detect cyanosis?
Pulse Oximetry
Why is pulse oximetry not useful In detecting anaemia?
-This is because the lungs are still working, so Hb would appear to be fully saturated.
What is pulse oximetry used for?
- Detects level of Hb saturation.
- –> It does this as it detects the difference in absorption of light between oxygenated and deoxygenated Hb.
- ———-> Oxygenated Hb absorbs less red light whilst deoxygenated Hb absorbs red light.
- pulse oximetry only detects pulsatile arterial blood.
- –> ignores levels in tissues and non-pulsatile venous blood.
- Doesn’t say how much Hb is present.
