Chapter 6: Gas Transport by the blood Flashcards
What is the Henry law?
describes that the amount dissolved is proportional to the partial pressure
for every 1 mmHg PO2 there is 0.003mL O2/100 mL blood
What are the parts of hemoglobin?
4 x Heme - iron porphyrin compound
globin - made up of 4 polypeptide chains - 2 alpha and 2 beta chains
What is Hemoglobin A?
Normal adult hemoglobin
What is hemoglobin F and how does it differ from hemoglobin A?
fetal hemoglobin - has a higher affinity to oxygen
What is ferrous versus ferric iron? How do you call hemoglobin with ferric iron?
ferrous iron is the normal hemoglobin bound iron that is capable of binding, carrying, and releasing O2
ferrous becomes ferric iron when oxidized –> poor at binding and releasing O2
ferric iron hemoglobin form = methemoglobin
Fe2+ ferrous (there’s 2 of us)
Fe3+ ferric
What is the O2 capacity?
the maximum amount of O2 that can combine with Hb, i.e., when all Hb binding sites are occupied by O2
Explain relaxed (R) versus tense (T) forms of Hb. How does this affect the O2 dissociation curve?
relaxed Hb is oxygenated - once Hb binds to an O2 molecule, O2 affinity increases
tense Hb is deoxygenated - more difficult for O2 to bin
creates the sigmoid O2 dissociation curve –> less steep in the beggining then very steep, then flattens when O2 binding sites are saturated
What is the equation for the O2 concentration of arterial blood?
(Hb x SaO2 x 1.36) + (0.003 x PaO2)
Explain why the sighmoid shape of the O2 dissociation curve is physiologically beneficial
benefits of the flat upper portion:
* even if alveolar gas falls somewhat - loading of O2 won’t be affected (does not apply to large PAO2 drops)
* steep lower part means peripheral tissues can withdraw a lot of O2 from Hb with only a small drop in capillary PO2 –> maintains pressure gradient needed for diffusion of O2 into the tissue cells
What is the full name of 2,3-DPG?
2,3-Diphosphoglycerate
Name 4 changes that can shift the O2 dissociation curve to the right
- increase in H+ (i.e., lower pH)
- increase in temperature
- increase in CO2
- increase in 2,3-DPG
exercising muscle is acidic, hot, and produces more CO2 and benefits more from O2
What does a right shift of the O2 dissociation curve mean?
Hb offloads O2 easier, i.e., O2 affinity of Hb is reduced
What is the Bohr effect?
increased PCO2 will decrease the Hb affinity to O2 - i.e., Hb will offload O2 easier at the tissue capillaries
mostly attributed to the CO2 ability to increase H+ (decrease pH)
Where is 2,3-DPG produced?
in the RBC - end product of RBC metabolism
How does 2,3-DPG change in chronic hypoxia?
2,3-DPG will increase –> will assist the offloading of O2 in peripheral tissues
How does 2,3-DPG change in stored blood?
stored blood tends to be depleted of 2,3-DPG - impaires O2 offloading
What value on the blood gas could be useful to determine the position (i.e., left or right shift) of the patient’s oxygen dissociation curve?
P50 - at 50% Hb what is the pO2?
should be 27 - if lower, left-shift, if higher - right shfit
what is the predicted PO2 for an SO2 of 97%m 75%, and 50%?
100 mm Hg
40 mm Hg
27 mm Hg
How does Carbonmonoxide affect the oxygen carryign capacity and tissue oxygenation?
CO will combine with Hb to form carboxyhemoglobin
CO affinity to Hb is 240 times that of O2 - will tie up most of the Hb even at low PCO
Will have a grossly reduced O2 concentration with a normal PO2 and Hb concentration
COHb will also shift the O2 dissociation curve to the left - additionally interfering with tissue oxygenation by impairing O2 offloading
What is the Gibb’s Donnan effect?
Describes the unequal movement of permeable charged ions on either side of a semi-permeable membrane in the presence of impermeable charged ions to achieve electroneutrality
What are the three forms of CO2 in the blood?
- Dissolved CO2 - follows Henry’s law - the more PCO2 the more dissolved CO2
- HCO3- /bicarbonate
- protein-bound CO2 - carbaminohemoglobin
How does the CO2’s solubility compare to that of O2?
CO2 is 24 times more soluble
Name the equation for bicarbonate formation from CO2 and explain it’s steps within the RBC
CO2 + H2O –> H2CO3 –> H+ + HCO3-
* first part is fast in the presence of carbonicanhydrase (CA), which is present in RBCs
* H2CO3 then diffuses easily to H+ and HCO3-
* HCO3- diffuses out of the RBC but H+ cannot
What is the chloride shift ?
when H2CO3 splits into HCO3- and H+, the HCO3- diffuses easily out of the cell but H+ cannot
to achieve electroneutrality, Cl- will move into the cell via the chlorida-bicarbonate exchanger
follows the Gibbs Donnan equilibirium
What is the Haldane effect and what causes it?
Reduced (deoxygenated) Hb has an increased ability to carry CO2 for 2 reasons:
- reduced Hb is less acidic (a better proton accepter) and can therefore take up the H+ after CO2 undergoes carbonic anhydrase in RBCs –> improves efficacy of HCO3- production
- reduced Hb is more effective at binding CO2 to its protein (globin)
How are Carbamino compounds formed?
By the binding of CO2 to the terminal amine groups of blood proteins
predominantly to the globin of hemoglobin forming carbaminohemoglobin
reduced Hb can bind more CO2 than oxygenated Hb (contributing to the Haldane effect)
How does the shape of the CO2 dissociation curve compare to the O2 dissociation curve
CO2 dissociation curve is much steeper, i.e., less change in PCO2 for changes in CO2 cc compared to PO2 changes from changes in O2 cc
What causes a right shift of the CO2 oxygenation curve
an increase in SO2
What is the underlying process leading to the dot moving
* from A to B and then D
* from A to C and then F
* from A to G and then F
* from A to E and then D
How do the kidneys respond to a respiratory acidosis
conserve HCO3-:
increased PCO2 in the renal tubular cells –> prompt excretion of more acidic urine (i.e., more H+ ions) by excreting H2PO4- and NH4+ –> HCO3- is then reabsorbed
Explain these 3 graphs
They demonstrate the tissue O2 delivery by capillaries
A: normal O2 delivery, even further distant cells in the middle are still adequately provided O2
B: critical O2 delivery - distant cells –> O2 delivery falls to zero
C: inadequate O2 delivery for aerobic metabolism –> anaerobic metabolism
explain cyanide poisoning
causes histotoxic hypoxia
prevents the use of O2 by cytochrome oxidase
venous O2 cc will be high but cells cannot consume O2
