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Module 9 > Gas Exchange + Transport: O2 > Flashcards

Gas Exchange + Transport: O2 Flashcards

1
Q

how do gases move in the alveoli and capillaries

A

gases move down concentration gradients by diffusion (same as pressure gradients)

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2
Q

what is gas partial pressures

A

air is a mixture of gases each of which exerts its own partial pressure (P) is independent of other gases

the total pressure is the sum of the partial pressure of each gas in the mixture Dalton’s law

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3
Q

what alters the partial pressure of O2

A

alters depending on other factors ex. atmospheric pressure (Patm)

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4
Q

how can PO2 be calculated

A

PO2 = Patm x Fo2

Patm = mmHg

Fo2 = mole fractional concentration of oxygen in air

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5
Q

what occurs to PO2 in the presence of water vapour molecules

A

reduces concentration of O2

PO2 is less in humidified air

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6
Q

how is PO2 of humidified gas in airways calculated

A

PO2 = (Patm - Ph2o) x FinhaledO2

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7
Q

where does gas exchange occur

A

in alveoli

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8
Q

what is the respiratory unit

A

airways branch into smaller and more numerous bronchioles until terminating to a group of alveoli

each division results in an increase in #, decrease in diameter, increase in surface area

  1. resp bronchioles
  2. alveolar ducts
  3. alveoli
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9
Q

what are the characteristics of alveoli

A
  1. large surfae area (~100m^2)
  2. very thin walls
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10
Q

identify the gas exchange structures

A
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11
Q

what is the pulmonary circuit

A

O2 enters blood

CO2 leaves

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12
Q

what is the systemic circuit

A

O2 leaves blood

CO2 enters

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13
Q

what is the difference between O2 and CO2 pressure gradient

A

pressure gradient for O2 is much bigger than for CO2

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14
Q

what are the partial pressures of gas gradients

A
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15
Q

how is O2 carried in the blood

A
  1. dissolved (measured clinically in arterial blood PaO2) –> very small %
  2. bound to hemoglobin (Hb)
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16
Q

what factors affect oxygen transport

A
  1. concentration of pigment
  2. rate of circulation (cardiac output)
  3. O2 affinity of pigment
17
Q

what is the concentration of pigments in oxygen transport

A

birds and mammals 15-20ml/100

lower in invertebrates with Hb 4-6ml/100ml

18
Q

how does rate of circulation affect oxygen transport

A

circulatory system of mammals and birds operates at leisurely pace at rest

during exercise O2 demand increases so circulatory system responds

rate of O2 delivery = cardiac output x (arterial [O2] - venous [O2])

increase in rate of blood flow + increase extraction of O2 = increase in O2

venous blood becomes much more deoxygenated than at rest

19
Q

what does degree of Hb oxygenation depend on

A

PO2

at high PO2 –> promotes O2 binding

at low PO2 –> reduces binding

20
Q

how does oxygen affinity of pigments affect oxygen transport

A

pigments that bind O2 at low PO2 = high affinity

pigments that require higher PO2 to bind to O2 = low affinity

21
Q

what is human Hb affinity for O2

A

relatively low affinity for O2

22
Q

why does human Hb have a low affinity for O2

A

lower affinity means O2 more difficult to bind to pigment but easier to release O2

23
Q

what factors affect O2 affinity

A
  1. pH and CO2 (Bohr effect)
  2. temperature
  3. ions
  4. organic compounds
24
Q

what is the bohr effect

A

oxygen affinity depends on the PCO2 and the pH

a decrease in pH or increase in PCO2 = decrease in O2 affinity

shifts the saturation curve right

25
Q

how does the bohr effect enhance O2 delivery

A

the bohr shift lowers affinity at tissues to increase O2 release

shifts back to higher affinity at lungs/gills to promote O2 uptake

26
Q

how does temperature affect O2 affinity

A

increase in temp decreases O2 affinity

enhance O2 delivery to muscles similar to bohr effect

27
Q

how does inorganic ions affect O2 affinity

A

ions in the blood can allosterically modulate O2 affinity of respiratory pigments

Cl ions in RBCs critical allosteric modulator

28
Q

how do organic compounds affect O2 affinity

A

2,3-diphosphoglycerate (DPG) reduces O2 affinity of Hb molecules it binds

human Hb continuously exposed to 2,3-DPG so constantly modulated by a normal DPG level

2,3-DPG is increase by chronic hypoxia, anemia and acclimation to high altitude

29
Q

what is cooperativity

A

binding at one site increases affinity at remaining sites

partially oxygenated Hb more likely to bind O2 than fully deoxygenated molecule

cooperativity enhances the responsiveness to changes in PO2

Module 9 (43 decks)

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