Ch. 6 West Flashcards
Oxygen is carried in the blood in what two forms
Dissolved
Combined with hemoglobin
Henry’s law states that the amount of dissolved oxygen in the blood is proportional to the partial pressure. For each mmHg of PO2, there is _____ mL O2 per 100 mL blood.
0.003
Thus, normal arterial blood with a PO2 pf 100 mmHg contains 0.3 mL O2 as dissolved O2 per 100 mL.
Oxygen forms an easily reversible combination with hemoglobin to give oxyhemoglobin via the following reaction:
O2 + Hgb ⇌ HbO2
The oxygen-hemoglobin dissociation curve shows that the amount of O2 carried by Hgb rapidly increases up till a PO2 of ___ mmHg then the curve becomes much flatter.
60 mmHg
T/F: The amount of oxygen bound by Hgb at any time is a function of the PO2
True
Oxygen saturation of Hgb formula
= [O2 combined with Hgb/O2 capacity] x 100%
How much oxygen (mL) can 1 gram of Hgb combine with?
1.39 mL
The oxygenated form of hemoglobin (the relaxed state) undergoes conformational change to its deoxygenated form, also called the _____ state
Tense state
Equation for oxygen concentration of blood (in mL O2 per 100 mL blood)
= [1.39 x Hgb x (% sat/100)] + 0.003(PO2)
Hgb in grams/100 mL
PO2 is in mmHg
T/F: Anemia will decrease O2 carrying capacity and O2 concentration but will not decrease the % saturation.
True
T/F: The steep lower part of the oxygen hemoglobin dissociation curve means that the peripheral tissues can withdraw large amounts of oxygen for only a small drop in PO2.
True
Why do polycythemic patients often appear cyanotic?
Because deoxyhemoglobin is purple in color; and cyanosis is determined by the proportion of deoxygenated hemoglobin
When the curve shifts to the right, O2’s affinity for hemoglobin is __________
Decreased
Factors which shift the O2/Hgb dissociation curve to the right:
Acidosis
Increased PCO2
Increased temperature
Increased 2,3-DPG in RBC’s
Explain the Bohr effect
Most of the effect of PCO2 on the oxygen-hemoglobin dissociation curve, can be attributed to its action on H+ concentration.
PO2 of 100 mmHg corresponds to a saturation of ____ %
97.5%
PO2 of 40 mmHg corresponds to a saturation of ___ %
75%
PO2 of 60 mmHg corresponds to a saturation of ____ %
90%
PO2 of 27 mmHg corresponds to a saturation of ____ %
50%
This is also called the P50
Carbon monoxide has ____ times the affinity of oxygen for hemoglobin
240 times
This means that CO will combine with the same amount of Hgb as O2 when the CO partial pressure is 240 times lower!
Why is the measured saturation potentially normal in CO poisoning patients?
Because technically the RBCs combined with O2 are saturated. Pulse ox measures oxyhemoglobin, not carboxyhemoglobin.
Small CO addition shifts the curve to the left, impairing oxygen offloading.
CO2 is carried in the blood in three forms:
Dissolved CO2
Bicarb
Combination with proteins such as carbaminos
Carbonic anyhydrase equation
CO2 + H2O ⇌(CA)⇌ H2CO3 ⇌ H+ + HCO3-
When the above reaction occurs in cells, HCO3- moves out of the cell, but the cell membrane is relatively impermeable to cations so H+ cannot move out. To maintain electroneutrality, which ion has to move into the cell from the plasma and by what exchanger does this occur?
Chloride
Chloride-bicarbonate exchanger
Also called the chloride shift
Some of the liberated hydrogen ions combine with reduced hemoglobin in the following manner:
H+ + HbO2 ⇌ H+ *Hb + O2
Reduced hemoglobin is less acidic than the oxygenated form and accepts protons better.
What is the Haldane effect?
Reduced hemoglobin in the peripheral blood accepts acids better and therefore helps with CO2 unloading.
Deoxygenation of the blood increases its ability to carry CO2.
The bulk of CO2 in the blood is as ______ and the dissolved form is small, and that which is protein bound is as the form of ______
The bulk of the CO2 in the blood is bicarb
A small amount is dissolved
The protein bound form is called carbaminohemoglobin
T/F: Bicarbonate reactions are the major source of expired CO2
True
T/F: Bicarb levels depend on the carbonic anhydrase in the cell
True
T/F: Transport of CO2 in solution (i.e. the dissolved portion) accounts for about 10% of the CO2 evolved by the lung.
True
T/F: Carbamino compounds are formed mainly with hemoglobin and account for about 30% of the CO2 evolved by the lung.
True
T/F: CO2 carriage in the form of carbaminohemoglobin is enhanced by deoxygenation of the blood.
True
Why is the PO2 difference between arterial and venous samples huge, but the difference between CO2 between arterial and venous samples is small?
The CO2 curve is steeper and shorter
The typical arterial and mixed venous blood difference in PO2 is typically close to ___ mmHg.
60 mmHg
The CO2 curve is shifted to the right by ______ (Haldane effect)
Increases in SO2
Oxygenation of blood in the lungs displaces carbon dioxide from hemoglobin, increasing the removal of carbon dioxide.
Carbon dioxide carriage in the blood in the form of carbaminohemoglobin is enhanced by deoxygenation of the blood.
As long as the ratio of bicarb concentration to (PCO2 x 0.03) remains equal to _____ , the pH will remain at 7.4.
20
Respiratory acidosis is caused by a ____ in PCO2, which reduces the HCO3/PCO2 ratio and therefore depresses the pH.
Increase in PCO2
Four causes of tissue hypoxia
1) Low PO2 in arterial blood caused by pulmonary disease (“hypoxic hypoxia”)
2) A reduced ability of blood to carry O2, as in anemia or CO poisoning (“anemic hypoxia”)
3) A reduction in tissue blood flow, either generalized as with shock, or because of local obstruction (“circulatory hypoxia”)
4) Toxic substance interfering with the ability of the tissues to use oxygen (“histotoxic hypoxia”), an example of which would be cyanide poisoning which prevents use of O2 by cytochrome oxidase
The acid-base status of the blood is determined by the ______ equation, especially the ratio of ____ to ____.
Henderson-Hasselbalch equation
Ratio of HCO3 to CO2
The PO2 in some tissues is less than ___ mmHg, and is much higher in the blood so that the gradient for diffusion is adequate.
5 mmHg
