gas transport in the blood 1 (R4) Flashcards
what happens to O2 picked up by blood at the lungs
it must be transported to the tissues for cellular use
what happens to CO2 produced at tissues
it must be transported to the lungs for removal
oxygen partial pressures around the respiratory system
PO2 (kPa) decreases as you go from atomsphere to the tissues
effect of partial pressure on gas solubility
(due to henry’s law)
-if the partial pressure in the gas phase is increased the concentration of the gas in the liquid phase would increase proportionally
henry’s law
-the amount of given gas dissolved in a given type and volume of liquid (eg. blood) at a constant temperature is; proportional to the partial pressure of the gas in equilibrium with the gas
partial pressure of a gas in solution
= its partial pressure in the gas mixture which it is in equilibrium
amount of O2 dissolved in blood
-proportional to the partial pressure (henry’s law)
-
volume of O2 per litre of blood
3ml (at a PO2 of 13.3 kPa)
volume of O2 taken to tissues as dissolved O2 under resting conditions (CO= 5L/min)
15ml/min
cardiac output (CO) under resting conditions
5L/min
volume of O2 taken to tissues as dissolved O2 during strenuous exercise (CO=30L/min)
90ml/min
resting O2 consumption of body cells
250ml/min
-may increase up to 25 folds during strenuous exercise
how is oxygen transported in the blood
-most O2 in the blood is transported bound to haemoglobin in the red blood cells
normal O2 concentration in arterial blood
- 20ml/100ml (200ml per L)
- > at a normal arterial PO2 of 13.3 kPa
- > and a normal haemoglobin concentration of 15 grams/100ml
normal arterial PO2
13.3 kPa
normal haemoglobin concentration in arterial blood
15 grams/100ml
% of O2 bound to haemoglobin
98.5%
% of O2 carried in the dissolved form
1.5% (3ml per litre at a PO2 of 13.3 kPa)
what are the two forms that O2 is present in the blood
- bound to haemoglobin
- physically dissolved (very little O2)
how does oxygen bind to haemoglobin
- haemoglobin can form a reversible combination with O2
- Each Hb molecule (made up of alpha and beta chains) contains 4 haem groups (each haem group contains an iron, Fe++, molecule which is responsible for the binding to O2)
- each haem group reversibly binds to one O2 molecule
- the binding of one O2 to Hb increases the affinity of Hb for O2 (co operativity causing sigmoid curve in oxygen haemoglobin dissociation curve)
when is haemoglobin considered fully saturated
when all the Hb present is carrying its maximum O2 load
what is the primary factor which determines % saturation of haemoglobin with O2
the PO2
oxygen haemoglobin dissociation curve explained
- the main determinant of % saturation of haemoglobin with O2 is the PO2, therefore as PO2 increases as does the O2 concentration and therefore %haemoglobin saturation
- as O2 concentration increases the haemoglobin becomes mores saturated with oxygen as more haem groups are filled up/bound to oxygen
- this eventually levels out when haemoglobin is completely saturated (100%) and there are no more haem groups that can bind to O2 therefore total O2 curve is greater than the O2 bound to Hb curve
- sigmoid curve produced due to cooperativity of haemoglobin (binding of one O2 to Hb increases affinity of Hb for O2)
- curve flattens when all sites are becoming occupied
- flat upper portions of curve means that moderate fall in alveolar PO2 will not affect oxygen loading greatly
- steep lower part of curve means that the peripheral tissues get a lot of oxygen for a small drop in capillary PO2 (all because PO2 determines haemoglobin saturation with oxygen)
- at low PO2, oxygen release occurs as it is not bound to Hb
DO2I
- oxygen delivery index (ml/min/metre squared)
- DO2I=CaO2 x CI
- (CaO2= oxygen content of arterial blood (ml/L))
- (CI=cardiac index (L/min/metre squared))
what is oxygen delivery to the tissues a function of
oxygen content of arterial blood and the cardiac output
DO2I= CaO2 x CI
CaO2
-oxygen content of arterial blood (ml/L)
-determined by the haemoglobin concentration [Hb] and the saturation of Hb with O2
=1.34 x [Hb] x SaO2
->1 gram of Hb carries 1.34ml of O2 when fully saturated
->[Hb] = haemoglobin concentration (gram/L)
-> SaO2 = % Hb saturated with O2, remember this is determined by PO2
CI
- cardiac index
- (L/min/metre squared)
- cardiac index relates the cardiac output to the body surface area (ie. the size of the individual)
- normal range for CI= 2.4 - 4.2 L/min/metre squared
PO2
- (partial pressure of oxygen)
- reflects the amount of oxygen gas dissolved in the blood.
- It primarily measures the effectiveness of the lungs in pulling oxygen into the blood stream from the atmosphere
average resting PO2 at systematic capillaries
5.3kPa
normal PO2 at pulmonary capillaries
13.3kPa
volume of O2 carried by 1 gram of Hb when fully saturated
1.34ml
[Hb]
-haemoglobin concentration (gram/L)
SaO2
- %Hb saturated with O2
- determined by PO2
what can impair oxygen delivery to the tissues
- respiratory disease
- heart failure
- anaemia
cooperativity of Hb
- binding of one O2 to Hb increases affinity of Hb for O2
- produces sigmoid curve of oxygen haemoglobin dissociation curve
bohr effect
- states that hemoglobin’s oxygen binding affinity is inversely related both to acidity and to the concentration of carbon dioxide.
- shifts the oxygen haemoglobin dissociated curve to the right, therefore conditions at the tissues causes an increased release of O2 from haemoglobin (conditions: increase in PCO2, increased H+/acidity, increased temperature, increased 2,3-biphosphoglycerate)
off loading of O2 at tissues
- tissue O2 tension and arterial O2 tension decrease (PO2) therefore % saturation of haemoglobin with O2, releasing O2 from haem groups
- arterial and tissue conditions also differ and tissue conditions cause a shift in curve to the right (bohr effect), furthermore ‘off loading’ O2
structure of haemoglobin/Hb
made up of 2 beta chains/subunits and 2 alpha chains/subunits which contain haem groups (iron, Fe++, is contained within haem group which is responsible for the binding of oxygen)
foetal haemoglobin
- (HbF)
- differs from adult haemoglobin in structure as HbF has 2 alpha and 2 gamma subunits (instead of 2 alpha and 2 beta)
- interacts less with 2,3-biphosphoglycerate in red blood cells, therefore HbF has a higher affinity for O2 compared to HbA/adult haemoglobin), this means that O2-Hb dissociation curve is shifted to the left for HbF
- this would allow more O2 to transfer from mother to foetus even if the PO2 is low
- foetal Hb is usually replaced with adult Hb within a few months after birth and oxygen dissociated curve shifts back to normal position
HbF
foetal haemoglobin
2,3- biphosphoglycerate
an isomeric ester of diphosphoglyceric acid that occurs in human red blood cells and facilitates release of oxygen by decreasing the oxygen affinity of haemoglobin
HbA
adult haemoglobin
why does HbF/foetal haemoglobin shift oxygen haemoglobin dissociation curve to the left
- interacts less with 2,3-biphosphoglycerate in red blood cells, therefore HbF has a higher affinity for O2 compared to HbA/adult haemoglobin), this means that O2-Hb dissociation curve is shifted to the left for HbF
- this would allow more O2 to transfer from mother to foetus even if the PO2 is low
myoglobin (Mb)
- present in skeletal and cardiac muscle
- has one haem group per myoglobin molecule
- no cooperative binding of O2 as a result of this
- has a hyperbolic dissociation curve
- releases O2 at very low PO2
- provides a short term storage of O2 for anaerobic conditions
- presence of myoglobin in blood indicates muscle damage
what does the presence of myoglobin in blood indicate
muscle damage
oxygen myoglobin dissociation curve
- hyperbolic
- levels off very quickly as myoglobin only has one haem group therefore is very quickly saturated
how many haem groups do each myoglobin molecule have
1
