Mech of gas exchange Lect 37 Flashcards
Equation of daltons law of partial pressures
the partial pressures of a gas in a mixture of gases is the pressure that gas would exert if it occupied the total volume of the mixture
Px=PB x F
- Px: partial pressure of gas
- PB: barometric pressure
- F: fractional gas
what happens to dalton’s law if gas is humidified
Px = (PB- PH2O) x F
- PH20 = 47 mmHg
What is the value for PH20 at 37 C
47 mm Hg
What the fraction of O2 (F) in inspired air
0.21
What is the value for barometric pressure (PB)
760mmHg
What are the values for PAO2 and PACO2 in alveolar air
- PAO2: 100mmHg
- PACO2: 40 mmHg
**blood leaving the alveoli has same values
- PaO2: 100mmHg
- PaCO2: 40 mmHg
O2 is transported in what two forms? What produces a partial pressure
- dissolved in blood: 2%
- bound to hemoglobin: 98%
- **ONLY dissolved O2 produces a partial pressure
what is the solubility constant of O2
0.003 ml O2/100 ml blood/mmHg
structure of hemoglobin molecule
- globular protein: 4 subunits
- 4 heme groups (contain reduced iron Fe2+)
- 4 polypeptide chaing (2 alpha and 2 beta)
- normal adult Hb = HbA
positive cooperativity
conformational changes expose remaining binding sites so other O2’s bind easier
describe Methemoglobin: hemoglobin variant
- iron part of heme in Fe3+ (ferric/oxidized form)
- Does NOT bind O2
Describe Fetal hemoglobin
- has higher affinity for O2 than adult HbA
- HbF = 2 alpha and 2 gamma chains
describe Hemoglobin S
- abnormal Beta chain (6th AA = valine instead of glutamic acid) -> Sickle cell disease
- O2 affinity of HbS is less than for HbA
equation for O2 content in blood
- O2 content = (O2 binding capacity x % saturation) + dissolved O2
- % saturation = % of heme groups bound to O2
What is the O2 binding capacity of blood?
hint: [Hb] in blood? 1 g Hb binds how much O2
- [Hb] in blood = 15 g/100mL blood
- 1 g Hb binds 1.34 ml O2
- this 15 x 1.34 = 20.1 ml O2/100 ml blood
what is the primary factor in determining percent hemoglobin saturation
PO2
- when blood PO2 is high, increased formation of HbO2 -> increased % saturation
oxygen-hemoglobin dissociation curve has what shape
sigmoidal
oxygen-hemoglobin dissociation curve levels off between what PO2 pressures
60-100 mmHg
* we can tolerate a decrease in PO2 ti 60mmHg without affecting the O2 carrying capability of Hb
P50
the PO2 where 50% of Hb is saturated
In tissues, PVO2 is what? What does this do to Hb saturation
- PVO2 is 40 mmHg
- Hb = 75% saturated
- O2 is not so tightly bound, facilitates better unloading of O2 at tissues
What does a shift to the right of the O2-hemoglobin dissociation curve indicate
- a decreased affinity of Hb for O2
- greater unloading of O2 in tissues
Name the 3 major factors that shift the O2-hemoglobin dissociation curve to the right
- Bohr Effect: increased PCO2 and decreased pH (more H+) -> increased metabolic activity
- increase in temperature
-
increase in 2,3-DPG
- binds to Hb and decreases affinity for O2
- seen in chronic hypoxia
shift to the left of the O2-hemoglobin dissociation curve indicates?
- increased affinity of Hb for O2
- less unloading of O2 in tissues
how much of CO2 is transported as bicarbonate HCO3-
90%
