Respiration 2 Flashcards by Sophie Chung

What are the fractional concentrations of different gases in dry air?

Nitrogen and inert gases = 0.79 (79%)

Oxygen = 0.21 (21%)

Carbon dioxide = 0.0004 (0.04%)

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Why do the fractional concentrations of gases change in humid air?

Water vapour present

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At rest, how much oxygen is consumed by tissues and how much carbon dioxide is produced per minute?

250ml oxygen

200ml carbon dioxide

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Why is the amount of oxygen used by tissues not equal to the amount of carbon dioxide produced?

Oxidation of organic fuel produces water as well

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What is the respiratory quotient?

0.8

Carbon dioxide produced/oxygen consumed

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What is alveolar ventilation at rest?

~4200ml/min

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Describe the volumes of oxygen transported around the body per minute.

250ml absorbed into blood from alveoli

Added to a 750ml reservoir

250ml used by cells

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How much oxygen is inhaled (into alveoli) and exhaled per minute (with calculations)?

0.21 x 4200 = 882ml inhaled into alveoli per min

882 - 250 = 632ml exhaled from alveoli per min

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What are the volumes of carbon dioxide being transported around the body per minute?

Tissues produce 200ml

Added to 2400ml reservoir

200ml expired

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What is the pressure exerted by a gas proportional to?

Temperature + number of gas molecules in a given volume

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What is Dalton’s law regarding pressure?

Individual pressure of a particular gas in a mixture of chemically inert gases is called the partial pressure

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What is the total pressure of a mixture of inert gases equal to?

Sum of all the partial pressures

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Describe how the partial pressure of oxygen changes through a breath.

21% in atmospheric air

Diluted by water vapour in upper airways

Absorbed into blood at alveoli (13.3) so decreases

Alveolar gas mixes with fresh air of anatomical dead space so increases

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Describe how the partial pressure of carbon dioxide changes through a breath.

Virtually 0 until gas exchange in alveoli (5.3)

Alveolar gas mixes with fresh air of anatomical dead space dilutes carbon dioxide

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Describe how the partial pressure of water vapour changes through a breath.

Variable in atmospheric air

Increases due to humidification in upper airways (6.3kPa)

Alveolar gas mixes with fresh air of anatomical dead space (variable)

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What is Henry’s law regarding dissolved gases?

Amount of gas dissolved in a liquid ∝ partial pressure of that gas in equilibrium with that liquid

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How does a gas diffuse?

From high to low partial pressures

Independent of other gases

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For an air-fluid system in equilibrium, how are the partial pressures related?

Air pp = fluid pp

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Why do we use partial pressures over concentrations of gases?

Easier to measure

Gives a better idea of movement

Concentration depends on solubility as well as pp

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What is the equation linking concentration, solubility and partial pressure?

Concentration = solubility x partial pressure

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How do systemic blood and alveolar partial pressures of oxygen change during gaseous exchange?

Systemic blood pp equilibrates to almost match alveolar pp

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How do blood and alveolar partial pressures of carbon dioxide change after gaseous exchange?

Alveolar pp equilibrates to exactly match blood pp

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What determines the rate of gaseous transfer (factors or equation)?

Partial pressure difference (P1 - P2)

Solubility of a gas in the fluid at 37°C

Diffusion barrier (SA/thickness)

Rate = (SA/thickness) x (P1 - P2) x S x (1/√mW)

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What is the partial pressure gradient of oxygen during gas exchange?

13.3 - 5.3 = 8kPa into blood

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How is the rate of gaseous exchange of oxygen limited?

Low solubility of oxygen in arterial blood

What is the partial pressure gradient of carbon dioxide during gas exchange?

5.3 - 6.1 = (-)0.8kPa out of blood

How efficient is gas exchange in the alveoli at rest?

Equilibrium is reached only one-third of the way along a pulmonary capillary

What are the partial pressures in blood straight after gas exchange?

Oxygen = 13.3kPa Carbon dioxide = 5.3kPa

Why is the partial pressure of oxygen in systemic blood not 13.3kPa?

Anatomical left to right shunt (bronchial) Drainage of part of coronary venous blood directly into left ventricle

What is the anatomical left to right shunt?

Deoxygenated bronchial vein blood mixes with and dilutes oxygenated pulmonary vein blood

How much of the cardiac output is deoxygenated?

~2%

What must the capillary partial pressure of oxygen be sufficiently high enough for?

To maintain partial pressure gradient to supply mitochondria

What is the partial pressure of oxygen in the mitochondria?

0.13kPa

How does gaseous transfer differ between alveoli and tissues?

Opposite direction of movement Transfer occurs along the whole capillary in tissues but in alveoli reaches equilibrium one-third along

What is 1dl in ml?

100ml

What is the solubility of oxygen and carbon dioxide in arterial blood?

0. 3ml/dl oxygen (in 13.3kPa pp) | 2. 74ml/dl carbon dioxide (in 5.3kPa pp)

What are the four important measures in oxygen transport?

Percent saturation Oxygen content Maximum oxygen carrying capacity Partial pressure

What is percentage saturation of oxygen?

Percentage of oxygen-binding sites on Hb that are bound to oxygen

What is oxygen content (ml/dl)?

Amount of gas present in blood = amount bound to Hb + amount dissolved in plasma

What is the maximum oxygen carrying capacity?

Amount of oxygen blood is capable of carrying when Hb is 100% saturated

What is the main determinant of amount of oxygen dissolved in the plasma and of percentage saturation?

Partial pressure of oxygen

What percentage of the oxygen content is carried by Hb?

98.5%

Why do we need haemoglobin?

Greatly increases amount of oxygen which can be carried by blood Oxygen solubility is low

What is the percentage saturation and oxygen content of blood entering pulmonary capillaries?

75% saturated 15ml/dl

Calculate the rate of oxygen circulation through the body per minute.

5L/min x 200ml/L = 1000ml/min | Cardiac output x oxygen content

Describe the structure of haemoglobin.

Quaternary structure protein 2 α-chains and 2 β-chains each with its own haem group Haem group contains a ferrous Fe2+ ion

What does the haem group bind to?

Histidine of globin molecule 1 molecule of oxygen

Why is the loading of oxygen onto haemoglobin referred to as oxygenation rather than oxidation?

Fe2+ remains in ferrous state

What is cooperative binding of haemoglobin?

Binding of one oxygen molecule increases the affinity of the remaining sites for oxygen

What causes the sigmoidal shape of the oxygen dissociation curve?

Cooperative binding

How much haemoglobin is in the blood normally?

15g/dl

What is the benefit of the exponential phase of the oxygen dissociation curve?

Oxygen consumption in tissues lowers pp Large drops in percentage saturation with small drops in pp aids unloading of oxygen where needed

What is the benefit of the plateau phase of the oxygen dissociation curve?

Large drops in pp cause only a small decrease in percentage saturation Supports oxygen uptake at low atmospheric pp or in respiratory disease

Describe the shift of the oxygen dissociation curve in the lungs and the factors affecting uptake.

Leftward shift (aids uptake) Loss of carbon dioxide = increased pH Evaporation lowers temperature Decreased [2,3-diphosphoglycerate]

Describe the shift of the oxygen dissociation curve in the tissues and the factors affecting uptake.

Rightward shift (aids unloading) Carbon dioxide produced = decreased pH Metabolism raises temperature Increased [2,3-diphosphoglycerate]

How can carbon dioxide be transported in the blood?

Dissolved Bicarbonate Carbamino compounds

Where is the carbon dioxide carried as bicarbonate found?

Dissolved in blood In erythrocytes

Describe the processes of RBC carrying bicarbonate.

Carbonic anhydrase accelerates conversion to bicarbonate H+ produced are buffered by Hb - Haldane effect A HCO3- exchanged for Cl-/chloride shift

How is carbon dioxide carried as carbamino compounds?

In erythrocytes, carbon dioxide reacts with amino groups of lysine and arginine residues of Hb - Haldane effect B

What is the Haldane effect A?

H+ produced in erythrocytes are buffered by Hb

What is the Haldane effect B?

In erythrocytes, carbon dioxide reacts with amino groups of lysine and arginine residues of Hb

In what form does haemoglobin form carbamino compounds more readily and what is the benefit of this?

Deoxy-Hb Removal of carbon dioxide at tissues

How is the majority of carbon dioxide carried in blood?

As bicarbonate

Describe the carbon dioxide dissociation curves.

Semi-linear over physiological pCO2 Greater amount of carbon dioxide carried by deoxygenated blood than oxygenated at any given pp (Haldane effect)

What are the values for carbon dioxide in arterial and venous blood?

Arterial = 48ml/dl, 5.3kPa Venous = 52ml/dl, 6.1kPa

What are the values for oxygen in arterial and venous blood?

Arterial = 20ml/dl, 12.5kPa Venous = 15ml/dl, 5.3kPa