gas exchange and transport

hypoxia

too little oxygen

hypercapnia

increased concentrations of carbon dioxide

what does the body do to avoid hypoxia and hypercapnia

responds to three regulated variable (o2, co2, pH)

what is arterial po2 value

95 mmHg

what is venous Po2 value

40 mm Hg

what is arterial Pco2 value

40 mm Hg

what is venous Pco2 value

46 mm Hg

what is normal pH

7.4

hypoxic hypoxia

low arterial po2

anemic hypoxia

decreased total amount of O2 bound to hemoglobin

ischemic hypoxia

reduced blood flow

histotoxic hypoxia

failure of cells to use O2, because cells have been poisoned

at the alveoli what is Po2 and Pco2

100 mm Hg, 40 mm Hg

in arterial blood what is Po2 and pco2

100 mm Hg, 40 mm Hg

in venous blood what is po2 and Pco2

40 mmHg, 46 mm Hg

what are the constants in healthy lungs

• diffusion distance

• membrane permeability

• surface area

what is the one variable

concentration gradient

emphysema

destruction of alveoli means less surface area for gas exchange

fibrotic lung disease

thickened alveolar membrane slows gas exchange. loss of lung compliance may decrease alveolar ventilation

pulmonary edema

fluid in interstitial space increases diffusion distance; arterial Pco2 may be normal due to higher co solubility in water

asthma

increased airway resistance decreases alveolar ventilation

what comes from O2 having low solubility

it means that very little O2 is transported by being dissolved in the plasma

does O2 or co2 diffuse more slowly across the respiratory membrane

o2

describe oxygen transport

• o2 entering alveolar capillaries dissolves in plasma first (only around 2% of it remains in the plasma

  • remaining o2 diffuses into erythrocytes and binds to hemoglobin (Hb)

oxyhemoglobin

HbO2

how many oxygen molecules can bind to each Hb

4

what is Hb saturation dependent on

plasma Po2

what is Q_{O2 (mL/ min)}

the rate of oxygen consumption by the body’s cells

on an Hb saturation curve what is the effect of decreasing pH

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on an Hb saturation curve what is the effect of decreasing pH

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on an Hb saturation curve what is the effect of increasing temperature

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on an Hb saturation curve what is the effect of decreasing temperature

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on an Hb saturation curve what is the effect of increasing pCO2

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on an Hb saturation curve what is the effect of decreasing pCO2

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on an Hb saturation curve what is the effect of increasing 2,3- BPG

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on an Hb saturation curve what is the effect of decreasing 2,3-BPG

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the total oxygen content of arterial blood depends on

the amount of oxygen dissolved in plasma and bound to hemoglobin

majority of o2 is converted to what for transport

bicarbonate

higher Pco2 leads to

lower pH

oxygen dissolved in plasma is influenced by

• composition of inspired air

• alveolar ventilation

• oxygen diffusion between alveoli and blood

• adequate perfusion of alveoli

alveolar ventilation is affected by

• rate and depth of breathing

• airway resistance

  • lung compliance

oxygen diffusion between alveoli and blood is affected by

• surface area

• diffusion distance

diffusion distance is affected by

• membranę thickness

• amount of interstitial fluid

oxygen bound to hb is influenced by

% saturation of HB and total number of binding sites

% saturation of Hb is affected by

Pco2, pH, temperature and 2,3-BPG

the total number of binding sites it influenced by

Hb content per RBC and number of RBCs