Haemoglobin and gas transport 1,2/ Flashcards
how much O2 is dissolved per litre of plasma?
3mL
why use haemoglobin? what is the blood’s O2 carrying capacity because of haemoglobin?
increases blood’s carrying capacity to 200mL/L
what proportion of CO2 is dissolved per litre of plasma?
the bulk of it
what phase do gases travel in the blood in?
they are dissolved in liquid, were they gaseous they would crete fatal air embolism
what is each haemoglobin chain attached to?
iron heme group
what does O2 bind to in the haemoglobin?
1 heme binds to oxygen, so 4 oxygens can be fixed by haemoglobin
what is cooperative binding, how is it relevant to haemoglobin?
cooperativity, because as O2 starts to bind, the conformation changes and makes it easier for more O2 to arrive, also when O2 leaves, conformation changes and makes it easier for th other O2 to leave (change in conformation changes affinity)
how many alpha and beta chains in HbA?
2 alpha and 2 beta
what is the lifespan of a red blood cells?
120 days
how oxygenated is deoxygenated blood?
75%
why is arterial partial pressure of O2 not the same as arterial O2 content?
because arterial partial pressure accounts for only the O2 dissolved in the blood, and not the O2 attached to haemoglobin
what is the relation between the partial pressure of a gas in solution and the partial pressure in gaseous phase (before it is driven into solution)
they are equal, i.e. the partial pressure at the alveoli is the same as the partial pressure inside the blood
what is O2’s solubility in water?
0,03mL/L/mmHg
how much plasma do we have per litre?
3mL/L plasma
what is the partial pressure driving O2 into the liquid phase in plasma (ie the partial pressure at the alveoli, also the partial pressure in solution)
3/0,03=100, 100 mmHg, known as the oxygen tension
what is the O2 demand of resting tissues?
250mL/min
what is the cardiac output?
5L/min
what is the rate of O2 delivery to tissue, counting only the O2 diluted in the plasma?
3mL/L x 5L/min = 15mL/min
what is the rate of O2 delivery to tissue, counting only the O2 carried by the hemes?
200mL/L x 5L/min = 1000mL/min
what percentage of arterial O2 is extracted by peripheral tissues at rest?
250mL/min : 1000mL/min
what is the percentage of O2 bound to haemoglobin?
1-(15/1000) = 98,5%
what percentage of Hb in RBC is in the form HbA? what does this form consist of? what makes up the rest of that percentage?
92%, 2 alpha and 2 beta chains. The remaining 8% is HbA2, HbF and glycosylated Hb
what does the HbA2 form consist of?
2 alpha and 2 delta
what does the HbF form consist of?
2 alpha and 2 gamma
which forms of Hb are glycosylated Hb?
HbA1a, HbA1b, HbA1c
what is the major determinant of the degree to which haemoglobin is saturated with oxygen?
the partial pressure of oxygen in arterial blood
where does Hb get its O2 from? the alveoli or the arterial plasma?
the plasma, that way there is a permanent partial pressure gradient between the alveoli and the arterial plasma, which means the arterial plasma is constantly filled up with O2 (to maintain 100 mmHg)
how long does it take for the Hb to become saturated?
0,25s contact time
what is the total contact time between alveoli and plasma?
about 0,75s
why is the partial pressure of O2 fundamental in binding to Hb?
it determines how much O2 binds to Hb
how saturated is Hb at the normal systemic arterial PO2 of 100mmHg?
almost saturated
how saturated is Hb at the systemic arterial PO2 of 60mmHg? what does this permit?
90% saturated, permits high uptake of O2 even when alveolar PO2 is moderately reduced
how saturated is Hb at the normal venous PO2?
75% saturated
How can Hb be saturated at any other level than 0, 25, 50, 75, 100? (because it only has 4 hemes)
the saturation number looks at all the Hb, a level of near saturation might correspond to most Hb having 4 O2 molecules, and a couple having only 3
rank myoglobin, foetal haemoglobin, normal haemoglobin in terms of affinity for O2, from less to most
normal haemoglobin, foetal haemoglobin, myoglobin
why has foetal Hb got more affinity for O2 than normal Hb?
because it draws its O2 from the mother’s blood, which has poorer O2 levels (as some O2 has already been taken for the mother’s systemic circulation)
is the relation between PO2 and saturation of Hb linear? why?
no (i.e. if PO2 decreases by 72%, there is only a 50% decrease in Hb O2 saturation), because of usage of more than 25% of the oxygen available (which is something it does under normal PO2) thanks to variations in Hb affinity
what is anaemia?
any condition where the oxygen carrying capacity of the blood is compromised
what happens to PaO2 in anaemia?
it would be the same because PaO2 is independent from any oxygen carrying elements
what happens to total blood O2 content in anaemia?
decreases
what might cause anaemia?
iron deficiency, haemorrhage, vitB12 deficiency
can you have a low PaO2 and normal blood O2 content?
no, PaO2 determines how saturated Hb becomes (Hb gets its O2 from the blood, where O2 pressure is determined by PaO2)
how saturated is Hb in an anaemic patient? (assuming normal PaO2)
100%, even though they have less Hb
how saturated is Hb in a patient with iron deficiency?
not 100% because iron deficiency affects the number of available hemes
what 4 factors make Hb saturation vary?
pH, PCO2, temperature and concentration of DPG
in certain conditions, the blood can “tap in” which O2 “reserve”?
O2 which accounts for 75% saturation of Hb in veinous blood (the rest of the 1000mL/min not used by tissues)
how do you call a shift to the right of an O2-Hb dissociation curve?
Bohr effect
how does the affinity of CO and O2 to Hb compare?
CO has affinity 250 times higher (binds easily, dissociates very slowly)
what consequences does this have?
CO displaces O2 and replaces it on Hb
why does this not cause any ventilation issue?
no higher levels of CO2, therefore no increase in ventilation
what is hypoxia? how many different types are there?
inadequate supply of oxygen to tissues, 5 types
what is hypoxic hypoxia? how common is it?
reduction in O2 diffusion at lungs because of tissue pathology or breathing in air with lower PO2, it is the most common type
what is anaemic hypoxia?
reduction in O2 carrying capacity of blood due to anaemia (RBC loss/ iron deficiency)
what is ischaemic (stagnant) hypoxia?
heart disease results in inefficient pumping of blood to lungs/ around the body
what is histotoxic hypoxia?
poisoning prevents cells utilising oxygen delivered to them (e.g.: carbon monoxide/cyanide)
what is metabolic hypoxia?
oxygen delivery to the tissues does not meet increased oxygen demand by cells
how would the body compensate for respiratory alkalosis?
hypoventilation
how would the body compensate for respiratory alkalosis?
hypoventilation
who would alveolar PO2 compare with arterial PO2 if oxygen was transported in blood without Hb?
alveolar PO2 = arterial PO2
what decreases affinity of haemoglobin for oxygen?
decrease in pH, increase in PCO2, increases in temperature
does this decrease in affinity exist locally?
yes, in actively metabolising tissues to facilitate the dissociation of oxygen from Hb
what increases affinity of Hb for O2?
rise in pH, fall in PCO2, fall in temperature
what consequences does this increase in affinity have?
makes oxygen unloading more difficult but aids collection of oxygen in the pulmonary circulation
affinity of Hb for O2 increases/decreases by binding to 2,3BPG?
decreases
what is 2,3BPG synthesised by?
erythrocytes
under what conditions would 2,3BPG levels rise?
situations associated with inadequate oxygen supply (heart or lung disease, living at high altitude)
what does the release of 2,3BPG do?
helps maintain oxygen release in the tissues
from what PCO can CO cause progressive carboxyhemoglobin formation?
0,4 mmHg
what are the symptoms of CO poisoning?
hypoxia, anaemia, nausea, headaches, cherry red skin, mucous membranes, potential brain damage, death
how does CO2 change ECF pH?
CO2 + H2O H2CO3 HCO3 + H+, and pH decreases if (H+) increases
how does the respiratory system maintain pH?
all the CO2 produced is eliminated in expired air
what happens if this balance is disrupted, and the body undergoes hypoventilation?
hypoventilation causes CO2 retention, leads to increased (H+) bringing about respiratory acidosis
what happens if this balance is disrupted, and the body undergoes hyperventilation?
hyperventilation blows off more CO2, leads to decreased (H+) bringing about respiratory alkalosis
