Carriage of Oxygen Flashcards
3 ways in which oxygen is transported in the body
Physically dissolved in plasma (~3 %)
combined with Hb as carbamino-haemoglobin (HbCO2) (3%)
Chemically bound to the haemoglobin molecule (Hb) in the red blood cells (RBC) (~92 %)
why is the percentage of oxygen dissolved in plasma so low
poor solubility of oxygen in plasma
what is haemoglobin Hb
heterotetramer consisting of 4 subunits (2 α and 2 β chains)
Each haemmolecule contains one ironatom
when oxygen is bound to haemoglobin what does it form
binds with iron to form oxyhaemoglobin
why is oxygens reversibility to being to bound to haemoglobin useful
allows O2 to be carried from the respiratory organs and released to the rest of the body
how many oxygen molecules can bind to Hb
4
allosteric affect of oxygen
Hb conformation from atensestate (loweraffinityfor oxygen) to arelaxed state(higheraffinityfor O2).
colour of oxygenated Hb, HboO2
Bright red (normal arterial blood
colour of deoxygenated Hb
dark red, blue
colour of carboxyhaemoglobin COHb
cherry red
oxygen content of blood
the amount of O2 in the blood (sum of both forms, dissolved and bound to Hb)
blood.
in a typical ml O2 per 100ml of blood name its oxygen content
(or volume %) = 0.3 ml (plasma) + 19.5 ml (RBC) = 19.8 ml/100 ml blood.
how do we calculate O2 blood content in tissue
Arterial O2 blood content - venous O2 blood content
oxygen carrying capacity of the blood
the maximum amount of O2 that can be carried by Hb. Each gram of Hb, when fully saturated, can combine with 1.34 ml of oxygen.
% saturation calculation
O2 content / O2 capacity
tool used to measure % saturation
pulse oximeter
how are arterial blood gas pressures measured
arterial blood samples and a blood gas analyser
P50 is the partial pressure of
oxygen
relationship of % saturation and PO2is a
sigmoid shape
plateau when percentage saturation is closest to 100%
why is it important that there is a plateau near 100% saturation
this is a protection against altitude and respiratory disease
cons of the plateau in sigmoid shape
however, the plateau reduces the usefulness of hyperventilation and O2 therapy
benefits of steep portion at start of graph reflecting in % saturation and PO2
allows for O2 unloading in the tissues
under what conditions can the increased affinity for O2 and there the left shift of the sigmoid shape occur
decrease in pCO2 partial pressure decrease hydrogen ions decrease 2,3 DPG decrease temp HbR
under what conditions can the decreased affinity for O2 and there the right shift of the sigmoid shape occur
increase in pCO2 partial pressure
increase hydrogen ions
increase 2,3 DPG
increase temp
bohr effect
in the tissues, the increase in PCO2 and H+ causes the haemoglobin to release more O2, the Bohr effect
that haemoglobin’s oxygen binding affinity is inversely related to both acidity and PCO2
what does the Bohr effect facilitate
O2 release from Hb at tissues (curve shifts right due to increased PCO2)
how does the bohr effect apply to 2,3 DPG
by an increase in temperature and 2,3-diphosphoglycerate
Where is DPG diphosphoglycerate
formed in the RBC and binds to the beta chains of haemoglobin causing O2 release
when is 2,3 DPG increased
increased in exercise, altitude, anaemia and respiratory disease and is reduced in stored blood
which haemoglobin binds to O2 better and why
haemoglobin F
or haemoglobin A
haemoglobin F (fetal) binds O2 better than haemoglobin A (adult) because 2,3-DPG binds poorly to the gamma chains of haemoglobin F - improves O2 transfer across placenta
where is myoglobin found and does it have a higher or lower affinity for O2 than Hb
myoglobin is found in skeletal and cardiac muscle. It has a higher O2 affinity than Hb and acts as a tissue store of O2
how is Hb saturation affected in anemia
not affected
how is arterial content reduced and why
but the arterial content of blood is reduced because the decreased amount of Hb per 100 ml blood decreases the O2 carrying capacity of the blood
in what direction does the CO shift the oxyhaemoglobin dissociation curve
to the left
what condition can CO lead to
severe tissue hypoxia
signs of cyanosis
blue colouration of the skin and mucous membranes, especially the tongue, mouth, lips and nail beds
when does cyanosis
it occurs when the arterial blood is 85% saturated (PO2=50 mmHg or 6.7 kPa) or when the capillary blood is 70% saturated (37.5 mmHg or 5 kPa)
central cyanosis is due to arterial blood desaturation
what causes cyanosis
due to reduced tissue blood flow due to vasoconstriction (exposure to cold, Raynaud’s disease etc.), vascular obstruction or decreased cardiac output (heart failure, shock etc.)
right shift in oxyhaemoglobin dissociation shift mean
increased oxygen unloading
chloride shift at tissue
CO2 diffuses in rbc -> bicarbonate in rbc then into plasma because of permeability of cell membrane to negative ions
Cell membranes. impermeable to charged ions - rbc can exchange bicarbonate w/ Cl wi/ an anion exchanger protein Band 3
rbc - positive charge - neutralised by entering Cl- ions
benefits of chloride shift at tissue
ensuresionicand electricalstability
duringthetransportofcarbondioxide
reverse chloride shift
O2 diffuses in rbc and CO2 diffuses out
O2 binds to haemoglobin and causes release of hydrogen
fall in RBC pH -> converts bicarbonate to CO2 and water
conc of bicarbonate falls -> bicarbonate exchanged w/ chloride
haldane effect
the deoxygenation of blood increases its ability to carry CO2
the loss of O2 allows Hb to bind more CO2 and H+ so more CO2 is carried as carbamino compoundsand as HCO3-
how does haldane effect affect pH
the pH falls from 7.4 in the arterial blood to 7.35 in the venous blood
conc of paCO2 during hyperventilation
“overbreathing” i.e. the PaCO2 is less than 40 mmHg
respiratory alkalosis
conc of PaCO2 during hypoventilation
means that the PaCO2 is greater than 40 mmHg
