6. Pulmonary blood flow and gas exchange 2+3: Haemoglobin +gas transport Flashcards
Why does the blood transport O2 from the lungs to the tissues?
to use O2 in energy production (and Co2 travels from tissues to lungs for removal)
How much O2 dissolves per litre plasma in ml?
3ml (solubility= 3/0.03ml/L/mm
Hg)
By how much does haemoglobin in RBCs increase O2 carrying capacity? (ml/L)
increases it to 200ml/L
How is a bulk of CO2 transported in the blood?
in solution in plasma (in various forms)
What is pulmonary circulation in terms of flow and pressure?
-high flow
-low pressure
system
What is the partial pressure gradient between alveoli and pulmonary arteries in mmHG for O2?
100mmHg (alveoli) to 40mmHg
What is the partial pressure of O2 in the air? (mmHg)
160mmHg
What is the partial pressure of O2 in tissues and veins? (mmHg)
40mmHg
Why isn’t the partial pressure of O2 in alveoli 160mmHg, and instead it’s 100mmHg?
when air enters the airways, it’s diluted down to 100mG by the time it travels down and reaches alveoli
What is the partial pressure gradient between pulmonary artery to alveoli in mmHG for CO2 (during removal)?
46mmHg to 40mmHg
Partial pressure gradient for O2 is 10 x greater than that for CO2, yet their rate of diffusion is quite similar- why?
because CO2 is much more soluble in water (which makes up for it)
What happens to pulmonary vessels if ventilation to an area of lung is compromised?(when O2 decreases and CO2 increases)
-local vasoconstriction in compromised region (pulmonary circulation only)
What does shunt refer to?
blood flowing through a poorly ventilated region without being oxygenated (it’s then redirected to better ventilated areas)
What does alveolar dead space refer to?
alveoli which are ventilated but not perfused
When can an alveolar dead space arise? (physiological)
when blood clot present blocking blood supply
Can ventilation in alveoli still occur when there is no blood perfusion?
yes
Why isn’t the partial pressure of O2 not the same as arterial content of O2?
because partial pressure only refers to O2 IN SOLUTION (the 3ml of O2 in plasma)
O2 in solution (how much O2 is dissolved in the plasma) is determined by what 2 factors?
- O2 solubility (which is fixed)
- partial pressure of O2 in gaseous phase (in alveoli)
both are driving O2 into solution
What is the general rule which drives the gas into solution?
value assigned to partial pressure of the gas in solution = partial pressure of gas in gaseous phase that is driving the gas into the solution
Describe the calculation that proves that partial pressure of O2 is 100mmHg (PP in alveoli)
- solubility of O2 in water is low; 0.03ml/L/mmHg
- we have 3ml/L of O2 in plasma so PP that is driving O2 into the liquid phase in plasma must be 100mmHg (3/0.03=100)
What is the general conclusion regarding PO2 in solution and gaseous phase.
the PO2 in solution= the PO2 in gaseous phase which results in that oxygen concentration in the liquid phase
What is another word for the PO2 (in arteries) which is at 100mmHg?- ie O2 arterial partial pressure
oxygen tension
Why do gases not travel in their gaseous phase in the plasma?
It would cause bubbles in the blood which could lead to fatal air embolisms
Why doesn’t the arterial PP of arteries not tell us anything about the oxygen levels?
because most of the oxygen is attached to haemoglobin in the plasma and not dissolved in the plasma (only 3ml)
Is O2 conc. higher in gaseous or liquid phase?
gaseous (because O2 isn’t dissolved in plasma (water))
Is this statement true?
Alveolar O2= Arterial O2
Yes
Describe the equation for O2 delivery
arterial O2 content x cardiac output = o2 delivery to tissues
3ml/L x 5L/min = 15ml/min (without haemoglobin, just pure O2 in solution)
What is the O2 demand of RESTING tissues?(how much O2 needed for tissues to function)
250ml/min
How much haemoglobin is there per litre in blood?
150g/L (there is 1.34ml O2 per g)
so 150x1.43=200ml/L
How much O2 WITH haemoglobin is found in the body?
1000ml/min
200ml/L x 5L/min
How much of arterial O2 is extracted by peripheral tissues at rest?
Only 25% ( 250ml/min is the O2 demand of resting tissues yet 1000ml/min of O2 is circulating in our blood)
Why do we have so much excess oxygen supply (with haemoglobin) in our blood and only 25% is used by resting tissues?
so body has excess O2 in reserve for actions such as exercise or increase in movement or body processes which need more energy
Each litre of systemic arterial blood contains approx. how much oxygen?
~200ml of oxygen
How much of the 200ml of oxygen in systemic arterial blood is bound to haemoglobin?
more than 98% (rest is dissolved in plasma)
How many haem groups and binding sites are associated with each
- 1 haem group
- 4 binding sites
How many molecules of oxygen bind to each haemoglobin?
4 molecules of oxygen
How much O2 in ml binds to each gram of haemoglobin?
1.34ml of O2
Is oxygenation and oxidation the same thing?
NO:
-oxidation is more lasting and permanent whereas oxygenation describes quick changes with O2 switching places
What is the most common type of haemoglobin that makes up 92% of our whole haemoglobin?
HbA
What 3 other forms of haemoglobin is the rest of haemoglobin made up of? (the remaining 8%)
- HbA2
- HbF
- glycosylated Hb (e.g. HbA1a)
What is the major determinant of the degree of haemoglobin saturation with O2 in arterial blood?
partial pressure of O2 in arterial blood
What binding process describes O2 binding to haem groups which make their sites more available for binding other O2 molecules?
cooperative binding
What is the life span of an RBC?
120 days
Why is glycosylated haemoglobin measured in diabetic patients?
to watch patient’s longterm glucose control (better indicator of glucose levels and intake than glucose and blood which can fluctuate more easily)
Partial pressure gradient that sucks O2 out of alveoli is maintained until what happens?
until the Hb becomes saturated with O2 (up to 98% of its maximum O2 carrying capacity)
Saturation of Hb is complete after how many seconds after contact with alveoli?
0.25 seconds (total contact time is ~0.75%)
What is fundamental in determining how much O2 binds to Hb?
partial pressure of O2 in plasma (as PO2 is increased in blood, the more O2 is pushed onto haemoglobin)
If PO2 decreased from 100mmHg to 60mmHg, would the haemoglobin remain highly saturated?
- Yes, it would still be ~90% saturated with O2 at 60mmHg (even 75% saturated at 40mmHg in veins ).
- this permits a relatively normal uptake of oxygen by the blood even when alveolar PO2 is moderately reduced
PP of oxygen has to roughly fall below which PP value before big losses of O2 occur?
below 60mmHg which emphasises the high affinity for O2 the Hb has
Why is the term “deoxygenated blood” slightly misleading?
the blood isn’t completely deoxygenated as even though it has a lower PO2 of 40mmHg, the Hb still has a relatively high saturation of approx. 75% in case the body requires a reserve of oxygen
What is the PO2 in arterial blood?
100mmHg
What is the PCO2 in venous blood?
40mmHg
What 2 molecules have a higher affinity for O2 than HbA ( which is the most common type of haemoglobin)?
- HbF (foetal haemoglobin)
2. myoglobin
Why do HbF and myoglobin have a higher O2 affinity?
so O2 can be easier extracted from maternal/ arterial blood
Which fibres in the body contain larger stores of myoglobin?
Oxidative fibres ( muscles) as they are more hungry for oxygen for efficient muscle function
Which fibres are not as hungry for O2 as oxidative fibres?
glycosidic fibres
If a patient’s PO2 falls to a drastically low level of 28mmHg for example (fallen by 72%), what would happen to the total O2 carrying capacity?
It would decrease by only 50%; which isn’t too big compared with the big drop in PO2 due to oxygen’s high O2 affinity.
What PO2 of O2 is regarded as the “death zone” in mmHg?
around 40mmHg and less (makes uptake of oxygen very difficult)
What is anaemia?
condition where the oxygen carrying capacity of the blood is compromised
What can cause anaemia? (3)
- iron deficiency (inadequate supply of iron)
- haemorrhage (e.g. trauma or burst ulcer)
- vitamin B12 deficiency
Why would PO2 be still normal in anaemic patients?
because PO2 refers to only O2 dissolved in solution which anaemic patients have no problem with- instead anaemics have problems with binding O2 to haemoglobin on RBCs which makes up VAST MAJORITY of the blood
Is it possible for an anaemic to have a normal PaO2 while total O2 content of blood is low?
Yes; as most O2 is on RBCs and not in solution so it’s possible to have a normal PaO2
Is it possible for anaemics to have a low PaO2 and a normal TOTAL O2 content?
No; as anaemics have a problem with the total O2 content in the blood (which is on RBCs)
What is the primary determinant of saturation of haemoglobin?
partial pressure of O2
In anaemics, is it possible for RBCs to be fully saturated with O2?
YES; in anaemia there is just less haemoglobin which means less O2 is carried in the body. But the haemoglobin that is in the body, is still nearly 100% saturated
What chemical factors change the affinity of haemoglobin for O2? (4)
- pH
- pPCO2
- Temperature
- DPG (2,3-diphosphoglycerate)
In venous blood at 40mmHg, what is the approx. saturation of haemoglobin?
around 75% (still very high)
What produces DPG? When is it produced
-RBCs (erythrocytes); produced in hypoxic conditions when PO2 falls
Who might have increased levels of DPG in their blood?
people living in high altitudes (also people with anaemia, hyperthyroidism, chronic alkalosis and chronic hypoxia)
What pH conditions decrease Hb affinity for O2?
pH decrease
What CO2 and temperature conditions decrease Hb affinity for O2?
increase in CO2 and increase in temperature
What is Bohr effect?
more oxygen is released in tissues that have higher CO2 absolute/relative values and a smaller pH (decreasing Hb affinity for O2)
Why does an increase in Co2 result in a decrease in pH?
because CO2 reacts with water to form carbonic acid reducing blood pH
Can Hb give up its O2 in extreme conditions to surrounding tissues?
Yes; in extreme circumstances where O2 is desperately needed to keep tissues alive
Conditions involving changes to pH, temperature and PCO2 exist locally or more widespread in the body?
exist locally in actively metabolising tissues
What effect does: -increase in temperature -increase in PCO2 -decrease in pH -DPG increase have on Hb affinity for O2?
facilitates the dissociation of O2 from Hb (causes Hb to lose its affinity for O2)
What effect does: -decrease in temperature -decrease in PCO2 -increase in pH have on Hb affinity for O2?
increase affinity of Hb for O2 (in pulmonary circulation)
DPG can be synthesised in situations that have inadequate O2 supplies, such as?
-high altitudes
-heart or lung disease
-hyperthyroidism
-anaemia
-chronic hypoxia
-chronic alkalosis
(helps maintain O2 release in the tissues)
What effect does DPG have on Hb affinity for O2?
affinity of Hb for O2 is decreased
CO binding to Hb forms what molecule?
carboxyhaemoglobin
How many times greater is the affinity of CO to Hb than O2 to Hb?
250 times greater
Why is CO very problematic once it dissolves in circulation?
because it binds very readily and dissociates very slowly
PCO of what pressure can cause progressive carboxyhaemoglobin formation?
PCO of only 0.4mmHg (not much needed to cause progressive damage)
What are some common symptoms of CO poisoning?
- hypoxia
- anaemia
- nausea
- headaches
- cherry red skin and mucous membranes
- potential brain damage and death
Why is respiration rate unaffected during CO poisoning?
due to normal arterial PCO2 (breathlessness doesn’t happen)
Define hypoxia
Inadequate supply of O2 to tissues.
What are 5 main types of hypoxia?
- hypoxic hypoxia
- anaemic hypoxia
- ischaemic (stagnant) hypoxia
- histotoxic hypoxia
- metabolic hypoxia
What is hypoxic hypoxia?
- most common
- reduction in O2 diffusion at lungs either due to decreased PO2(atmos) or tissue pathology
- affects often people at high altitudes due to low PaO2
What is anaemic hypoxia?
-reduction in O2 carrying capacity of blood due to anaemia (RBC loss/ iron deficiency/haemorrhage)
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. CO or cyanide
What is metabolic hypoxia?
- O2 delivery to the tissues does not meet increased O2 demand by cells
- system not adapted
- more likely to be transient (not permanent)
CO2 moves out of cells along or against its partial pressure (PP) gradient?
Along (down its PP gradient)
When CO2 diffuses from tissues into blood, how much remains dissolved in the plasma and eythrocytes?
only 7% of CO2
When CO2 diffuses from tissues into blood, how much combines in erythrocytes with deoxyhaemoglobin to form carbamino compounds?
23% of CO2
When CO2 diffuses from tissues into blood, how much combines in the erythrocytes with water to form carbonic acids?
70% of CO2
What does the carbonic acid produced from CO2 and water, then dissociates to yield?
bicarbonate and H+ ions
What happens to bicarbonate ions released from carbonic acid?
- moves out of erythrocytes and into the plasma in exchange for Cl ions (chloride shift)
What happens to excess H+ ions released from carbonic acid?
they bind to deoxyhaemoglobin in erythrocyte
How does the bicarbonate ion end up in the alveoli?
- it’s transported to lungs through various circulation
- reverse process occurs in pulmonary capillary (reverse to systemic capillary process)
- dissolved CO2 moves into alveoli down its conc. gradient
Is arterial or venous blood is better at buffering H+ ions?
venous(better at carrying Co2 than arterial blood)
When is Hb most likely to attach to CO2?
Once O2 levels fall and O2 is lost
What equation allow Co2 to change ECF pH?
CO2+H2O->H2CO3->HCO3 +H
CO2 into carbonic acid into bicarbonate and H
How does constant CO2 expiration affects the pH?
it maintains a stable and constant pH in the body
Can hypoventilation and hyperventilation alter plasma PCO2 and cause plasma H variation?
Yes; it can alter plasma PCO2
How does hypoventilation affect the pH? (on a molecular level)
- causes CO2 retention (nervous person)
- leads to increase in H (shift equation to the right)
- brings about respiratory acidosis
How does hyperventilation affect the pH? (on a molecular level)
- blowing off more CO2 (relaxed person)
- leads to decrease in H (shift to the left)
- brings about respiratory alkalosis
