Flashcards in *Physiology 3 (lecture 4) Deck (35)
What is Henry's law?
The amount of a given gas dissolved in a given type of liquid (e.g. blood) at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid
What is the partial pressure of a gas in solution equal to?
Its partial pressure in the gas mixture with which it is in equilibrium with
What are the 2 mechanisms by which oxygen is carried by the blood?
Oxygen bound to haemoglobin (98.5% of O2 carried in this way)
How many ml of O2 is normally carried in 1L of blood?
200ml (at a normal arterial PO2 of 13.3kPa and a normal haemoglobin concentration of 15g/ 100ml
How many harm groups does each haemoglobin contain?
How many oxygens does each haem group reversibly bind?
When is haemoglobin considered as fully saturated?
When all the Hb present is carrying its maximum O2 load
What is the primary factor which determines the percentage saturation of haemoglobin with O2?
What is Hb made up of?
2 alpha chains
2 beta chains
4 harm groups each with an iron which binds 1 O2
What is the normal PO2 at pulmonary capillaries?
What is the average resting PO2 at systemic capillaries?
What shape does an oxygen haemoglobin dissociation curve have?
A sigmoid shape
What does the cardiac index do?
Relates the cardiac output to the body surface area
Normal range is between 2.4 - 4.2 L/min/metre2
What are the units of the oxygen delivery index? (DO21)
What are the units of the oxygen content of arterial blood?
What does DO2I=?
DO21=CaO2 X CI
What does CaO2=?
CaO2 = 1.34 X [Hb] X SaO2
How many ml of O2 does 1 gram of Hb carry when fully saturated?
Units of [Hb]?
What determines SaO2?
What factors can impair oxygen delivery to the tissues? (4)
Decreased partial pressure of inspired oxygen
What does partial pressure of inspired oxygen depend on? (2)
Total pressure (i.e. atmospheric pressure)
Proportion of oxygen in gas mixture (about 21% in atmosphere)
What does binding of one O2 to Hb cause?
An increase in the affinity of Hb for O2 (co-operativity)
What shape is the oxygen haemoglobin dissociation curve?
What does the flat upper portions of the oxygen haemoglobin dissociation curve mean?
Moderate fall in alveolar PO2 will not much affect oxygen loading (very protective)
What does the step lower part of the oxygen haemoglobin dissociation curve mean?
The peripheral tissue gets a lot of oxygen for a small drop in capillary PO2
What is it called when the oxygen haemoglobin dissociation curve is shifted to the right?
What can cause this?
Bohr effect (increased release of O2 by conditions at the tissues)
Increased levels of 2,3-Biphosphoglycerate (will bind better to the deoxygenated haemoglobin compared to the oxygenated haemoglobin promoting partially emptied haemoglobin to release the rest of its oxygen)
(features of metabolically active cells will shift the curve to the right facilitating the release of oxygen from haemoglobin)
How does foetal haemoglobin differ from adult haemoglobin?
Foetal haemoglobin (HbF) has 2 alpha and 2 gamma subunits
Why does HbF have a higher affinity for oxygen compared to adult Hb?
HbF interacts less with 2,3-Biphophoglycerate in RBCs (shifts the O2-Hb dissociation curve to the left)
What is on the left on a O2-Hb dissociation curve, foetal or maternal?
What does this allow?
Foetal - due to HbF having a higher affinity for O2 compared to HbA
O2 to transfer from mother to foetus even if the PO2 is low
Where is myoglobin present?
In skeletal and cardiac muscles
How many harm group is present per myoglobin molecule?
1 (therefore no co-operative binding of O2)
Shape of Mb (myoglobin) dissociation curve?
What is the purpose of myoglobin?
To provide a short term storage of O2 for anaerobic conditions