BPK 205 > Lecture 26 > Flashcards

Lecture 26 Flashcards

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1
Q

what is the composition of the air we breathe

A
  • mix of gases
  • 78% N2
  • 21% O2
  • 0.033% CO2
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2
Q

what is daltons law

A
  • the total pressure exerted by a mixture of gases is the sum of pressures exerted by all individual gases
  • the pressure exerted by individual gas is called the partial pressure of that gas
  • total air pressure Patm = PN2 +PO2+PCO2
  • in humid air Patm= PN2+PO2+PCO2+PH2O
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3
Q

what is daltons law of partial pressures in dry and humid air

A
  • dry air (Pgas = Patm x % of gas in atmosphere)
  • humid air Pgas = (Patm-PH2O) x% of gas in atmosphere
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4
Q

what is the gas composition in the alveoli and atmosphere

A

in the atmosphere
-> PO2= 160mmHg
-> PCO2 = 0.25 mmHG
-alveolar partial pressures remain relatively constant during quiet breathing
-> PO2 = 100 mmHg
-> PCO2 = 40mmHg
- can vary with hypo or hyperventilation
- as alveolar ventilation increases, alveolar PO2 increases and PCO2 decreases
- the opposite occurs as alveolar ventilation decreases

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5
Q

what are the steps of pulmonary gas exchange and transport

A
  1. oxygen enters the blood at alveolar capillary interface
  2. oxygen is transported in blood, dissolved in plasma or bound to hemoglobin inside RBCs
  3. oxygen diffuses into cells
  4. CO2 diffuses out of cells
  5. CO2 is transported dissolved, bound to hemoglobin or as HCO3-
  6. CO2 enters alveoli at alveolar capillary interface
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6
Q

explain gas exchange across cellular barriers

A
  • O2 and CO2 diffuse across alveolar epithelial cells and capillary endothelial cells
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7
Q

how is diffusion of gas governed by Ficks law

A
  • rate of diffusion is directly proportional to
    -> surface area
    -> membrane permeability (D=diffusion constant)
    -> concentration (partial pressure) gradient
  • rate of diffusion is inversely proportional to
    -> diffusion distance (T)
    -> membrane thickness
    -> interstitial fluid
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8
Q

how do gases diffuse down their partial pressure gradients

A
  1. air moves by bulk flow down pressure gradients between atmosphere and alveoli
  2. pulmonary circulation
    -> alveolar PO2> venous blood PO2
    -> alveolar PCO2< venous blood PCO2
  3. systemic circulation
    -> arterial PO2> tissue PO2
    -> arterial PCO2< tissue PCO2
  • diffusion reaches equilibrium under normal circumstances
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9
Q

what are the factors that affect alveolar gas exchange

A
  • inefficient exchange can lead to low O2 content in the blood
  • O2 reaching the alveoli
    -> composition of inspired air
    -> alveolar ventilation ->rate and depth of breathing, airway resistance, lung compliance
  • > gas diffusion between alveoli and blood -> surface area, diffusion distance -> barrier thickness, amount of fluid
    -> adequate perfusion of alveoli
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10
Q

what are the factors that decrease the amount of O2 reaching the alveoli

A
  • low O2 content in the atmosphere
  • low alveolar ventilation
    -> decreased lung compliance (how easily they can expand)
    -> increase airway resistance
    -> CNS depression (drugs, alcohol overdose)
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11
Q

what can impair rate of gas exchange

A

diffusion rate = SA x barrier permeability x partial pressure gradient/ distance^2

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12
Q

what are the 4 pathological conditions that cause hypoxia

A
  • emphysema
  • asthma
  • fibrotic lung disease
  • pulmonary edema
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13
Q

explain emphysema

A
  • destruction of alveoli means less surface area for gas exchange
  • destruction of alveoli by cigarette smoke
  • affects surface area and partial pressure gradient
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14
Q

explain asthma

A
  • increased airway resistance decreases alveolar ventilation
  • bronchioles constricted
  • affects partial pressure gradient
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15
Q

explain fibrotic lung disease

A
  • thickened alveolar membrane slows gas exchange
  • loss of lung compliance may decrease alveolar ventilation
  • build up of scar tissue around alveoli by particulate irritants (asbestos)
  • affects partial pressure gradient and distance^2
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16
Q

explain pulmonary edema

Study These Flashcards
A
  • fluid in interstitial space increases diffusion distance
  • arterial PCO2 may be normal due to higher CO2 solubility in water
  • exchanged surface normal, increased diffusion distance
  • increase in interstitial fluid in lungs often a results of heart failure
  • affects distance^2
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