Respiration 2 Flashcards
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%)
Why do the fractional concentrations of gases change in humid air?
Water vapour present
At rest, how much oxygen is consumed by tissues and how much carbon dioxide is produced per minute?
250ml oxygen
200ml carbon dioxide
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
What is the respiratory quotient?
0.8
Carbon dioxide produced/oxygen consumed
What is alveolar ventilation at rest?
~4200ml/min
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
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
What are the volumes of carbon dioxide being transported around the body per minute?
Tissues produce 200ml
Added to 2400ml reservoir
200ml expired
What is the pressure exerted by a gas proportional to?
Temperature + number of gas molecules in a given volume
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
What is the total pressure of a mixture of inert gases equal to?
Sum of all the partial pressures
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
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
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)
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
How does a gas diffuse?
From high to low partial pressures
Independent of other gases
For an air-fluid system in equilibrium, how are the partial pressures related?
Air pp = fluid pp
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
What is the equation linking concentration, solubility and partial pressure?
Concentration = solubility x partial pressure
How do systemic blood and alveolar partial pressures of oxygen change during gaseous exchange?
Systemic blood pp equilibrates to almost match alveolar pp
How do blood and alveolar partial pressures of carbon dioxide change after gaseous exchange?
Alveolar pp equilibrates to exactly match blood pp
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)
What is the partial pressure gradient of oxygen during gas exchange?
13.3 - 5.3 = 8kPa into blood
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?
- 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
