Respiratory 7 Flashcards
Amount of oxygen bound to Hb depends on
Plasma O2 (RBC and cytosol PO2) and amount of hemoglobin
What does plasma O2 determine
% saturation of Hb
Plasma O2 is determined by
Alveolar PO2
What does alveolar PO2 depends on
1, composition of inspired air
2. Alveolar ventilation rate
3. Efficiency of gas exchange (normal for healthy)
What does the amount of hemoglobin determine
Amount of Hb binding sites
What is the total number of Hb binding sites calculated from
Hb content per RBC x Number of RBCs
What is anemia
Reduced carrying capacity of O2 in blood
What is the amount of O2 bound to Hb at any given PO2 expressed as
Percent saturation of hemoglobin (for any given pO2, Hb is a certain % saturated)
What determined the % saturation of Hb
PO2 that Hb is exposed to
What type of cells can have a lower PO2
Active cells (curve steep)
Can be as low as 20mmHg but larger release of O2
If PO2 100 how saturated us Hb
98.5%
When does more significant changes in saturation begin
Po2 below 60 mmHg
What physical factors alter hemoglobin’s affinity for O2
Levels of CO2, pH, temperature, 2,3-BPG
Shift in hemoglobin saturation as a result in pH or CO2 change
Bohr effect
What causes fast decreasing shift in pH
Active cells (max exertion)
- produces excess CO2, results in increased H+ and lactic acid in cytoplasm and extracellular space
- decrease pH, high acid, slight conformation in Hb
What does high pH cause
Reduced H+ and structural change in Hb and change affinity
What is CO2 readily converted into
Acid
H+ + HCO3
What does increased CO2 production cause
- CO2 readily binds Hb altering conformation (O2 released)
- CO2 readily converted to acid
What does increased heat at level of tissues cause
Conformational change in Hb leading to decreased affinity and more O2 dropped at active muscles
What is the metabolic compound 2,3-BPG
A by-product of glycolysis in RBC’s
What increases 2,3 DPG
Chronic hypoxia
RBCs release ATP during hypoxia
How does ascent to high altitude (low PO2) and anemia affect 2,3 BPG
Increases production
What oxygen binding properties do fetuses have to increase binding affinity of Hb
Two alpha, two gamma globin subunits
What does the different oxygen binding properties facilitate
Uptake of O2 into fetus even when exposed to lower PO2
Why is there lower PO2 fro fetus
No direct connection between mother and fetus
O2 lost in intervillous space
What is the importance of removing CO2 from body
- Elevated PCO2 causes acidosis
- Abnormally high PCO2 depresses CNS causing confusion, coma, or death
What does acidosis cause
Low pH leads to interruptions in hydrogen bonds and denaturing of proteins
How much CO2 carried by venous blood is dissolved in plasma
7%
Even though co2 very soluble, cells produce too much for plasma to be capable of carrying
Where does remaining 93% CO2 diffuse
Red blood cells
- 23% binds to hemoglobin HbCO2 (open sites after O2 released)
- 70% is converted to HCO3- (bicarbonate)
What are 3 ways CO2 is transported
- Dissolved in plasma 7%
- Bound to hemoglobin 23% (in RBCs)
- Converted to bicarbonate 70% (in RBCs)
What does carbonic anhydrase do
Converts CO2 when in excess to HCO3 and H+
Hb picks up H+
When HCO3 enters plasma why does in exchange for Cl
Ensures charge of RBC remains normal
What is happens to CO2 in reverse reaction
CO2 unbind Hb and diffuses out of RBC
Carbonic acid reaction reverses, pulls HCO3 back into RBC converting back to CO2
What 2 purposes does the conversion of CO2 to HCO3 serve
- Provide additional means of CO2 transport from cells to lungs (can take up as much as possible without contributing to partial pressure)
- HCO3 is available to act as buffer for metabolic acids, stabilizing body’s pH (binds to acids)
What is the reaction involving carbonic anhydrase
CO2 + H20 <-> H+ + HCO3-
Excess CO2 ——>
Low CO2 <—————-
What does the conversion of CO2 to HCO3 and H+ continue until
Equilibrium
What mechanisms exist to ensure equilibrium is not reached for CO2 to HCO3 and H+
Remove HCO3 from RBC (Chloride exchanger)
Mop up excess H+. (Hb binds and buffers acid)
What does Hb binding to excess H+ as buffer do
- prevents large changes in body’s pH
What causes Hb to not be able to carry out as buffer
If blood CO2 too high Hb cannot soak up all the H+ and respiratory acidosis can result
