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physiology final > Mech of gas exchange Lect 37 > Flashcards

Mech of gas exchange Lect 37 Flashcards

1
Q

Equation of daltons law of partial pressures

A

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
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2
Q

what happens to dalton’s law if gas is humidified

A

Px = (PB- PH2O) x F

  • PH20 = 47 mmHg
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3
Q

What is the value for PH20 at 37 C

A

47 mm Hg

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4
Q

What the fraction of O2 (F) in inspired air

A

0.21

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5
Q

What is the value for barometric pressure (PB)

A

760mmHg

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6
Q

What are the values for PAO2 and PACO2 in alveolar air

A
  • PAO2: 100mmHg
  • PACO2: 40 mmHg

**blood leaving the alveoli has same values

  • PaO2: 100mmHg
  • PaCO2: 40 mmHg
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7
Q

O2 is transported in what two forms? What produces a partial pressure

A
  • dissolved in blood: 2%
  • bound to hemoglobin: 98%
  • **ONLY dissolved O2 produces a partial pressure
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8
Q

what is the solubility constant of O2

A

0.003 ml O2/100 ml blood/mmHg

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9
Q

structure of hemoglobin molecule

A
  • globular protein: 4 subunits
    • 4 heme groups (contain reduced iron Fe2+)
    • 4 polypeptide chaing (2 alpha and 2 beta)
  • normal adult Hb = HbA
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10
Q

positive cooperativity

A

conformational changes expose remaining binding sites so other O2’s bind easier

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11
Q

describe Methemoglobin: hemoglobin variant

A
  • iron part of heme in Fe3+ (ferric/oxidized form)
  • Does NOT bind O2
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12
Q

Describe Fetal hemoglobin

A
  • has higher affinity for O2 than adult HbA
  • HbF = 2 alpha and 2 gamma chains
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13
Q

describe Hemoglobin S

A
  • abnormal Beta chain (6th AA = valine instead of glutamic acid) -> Sickle cell disease
  • O2 affinity of HbS is less than for HbA
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14
Q

equation for O2 content in blood

A
  • O2 content = (O2 binding capacity x % saturation) + dissolved O2
    • ​% saturation = % of heme groups bound to O2
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15
Q

What is the O2 binding capacity of blood?

hint: [Hb] in blood? 1 g Hb binds how much O2

A
  • [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
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16
Q

what is the primary factor in determining percent hemoglobin saturation

A

PO2

  • when blood PO2 is high, increased formation of HbO2 -> increased % saturation
17
Q

oxygen-hemoglobin dissociation curve has what shape

A

sigmoidal

18
Q

oxygen-hemoglobin dissociation curve levels off between what PO2 pressures

A

60-100 mmHg

* we can tolerate a decrease in PO2 ti 60mmHg without affecting the O2 carrying capability of Hb

19
Q

P50

A

the PO2 where 50% of Hb is saturated

20
Q

In tissues, PVO2 is what? What does this do to Hb saturation

A
  • PVO2 ​is 40 mmHg
  • Hb = 75% saturated
    • O2 is not so tightly bound, facilitates better unloading of O2 at tissues
21
Q

What does a shift to the right of the O2-hemoglobin dissociation curve indicate

A
  • a decreased affinity of Hb for O2
  • greater unloading of O2 in tissues
22
Q

Name the 3 major factors that shift the O2-hemoglobin dissociation curve to the right

A
  1. Bohr Effect: increased PCO2 and decreased pH (more H+) -> increased metabolic activity
  2. increase in temperature
  3. increase in 2,3-DPG
    1. binds to Hb and decreases affinity for O2
    2. seen in chronic hypoxia
23
Q

shift to the left of the O2-hemoglobin dissociation curve indicates?

A
  • increased affinity of Hb for O2
  • less unloading of O2 in tissues
24
Q

how much of CO2 is transported as bicarbonate HCO3-

A

90%

25
Q

what enzyme is responsible for converting CO2 into H2CO3

A

carbonic anhydrase

CO2 + H2O -> H2CO3

26
Q

Where does CO2 transport occur? List steps

A
  • in RBC
  1. CO2 + H2O -> H2CO3
  2. H2CO3 dissociates into H+ and HCO3-
  3. H+ stays in RBC and is buffered by deoxyhemoglobin
  4. HCO3- is transported into plasma in exchange for Cl-
27
Q

How is HCO3- transported into plasma from RBC

A

in exchange for Cl-

28
Q

H+ stays in the RBC and is buffered by

A

deoxyhemoglobin

29
Q

What happens to HCO3- released from RBC (via anion exchanger)

A

carried to lungs in venous blood

30
Q

haldane effect

A

In the lungs, CO2 is released from RBC

physiology final (7 decks)

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