Term
| How much O2 do cells consume at rest? |
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Definition
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Term
| How much CO2 do cells produce at rest? |
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Definition
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Term
| How much does the average male inhale per min? |
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Definition
| inhales 6000mL (so, 6L) of air |
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Term
| How much of this reaches the alveoli? |
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Definition
| 4200mL of this 6000mL reaches the alveoli. |
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Term
| How much of the air that reaches the alveoli is o2? |
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Definition
| 880mL (21%) of the 4200mL that reaches the alveoli is O2 |
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Term
| How much of the o2 that reaches alveoli diffuses into blood? |
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Definition
| 250mL of the 880mL that is O2 diffuses into blood. |
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Term
| What happens to the remaining O2? |
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Definition
| the remaining 630mL of O2 from the 880mL is exhaled. |
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Term
| How much O2 does the body consume every day? |
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Definition
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Term
| What are the essential primary symbols? |
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Definition
P: pressure or partial pressure
V: volume of gas
Q: flow of blood |
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Term
| What are the essential secondary symbols? |
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Definition
A: alveolar (PAO2)
a: arterial (PaCO2)
V: venous (PVO2) |
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Term
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Definition
| in a mixture of gases, each gas present in the mixture contributes to the total pressure of the gas’ |
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Term
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Definition
| In a mixture of gases, each gas has a partial pressure, which is the hypothetical pressure of that gas if it alone occupied the volume of the mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of each individual gas in the mixture. |
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Term
| What is resting O2 consumption? |
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Definition
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Term
| Describe diffusion in the capillary beds in the lungs (pulmonary capillaries) |
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Definition
O2 diffuses from the alveolar air to capillary blood
CO2 diffuses from capillary blood to alveolar air |
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Term
| Describe diffusion in the systemic capillary beds |
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Definition
O2 diffuses from the blood to the cells (via ISF)
CO2 diffuses from the cells to blood (via ISF) |
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Term
| How do gases diffuse when in a gas mixture? |
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Definition
down partial pressure gradients (high to low)
each gas has it's own gradient independent from the others |
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Term
| What is total air pressure at sea level? |
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Definition
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Term
| If total air pressure at sea level is 760mmHg and O2 occupies 21%, what is PO2? |
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Definition
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Term
| What does Fick's Law state? |
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Definition
the rate of diffusion of a gas through a sheet of tissue is directly proportional to the area (A), the partial pressure difference (P1 - P2) and the diffusion constant (D)
and is inversely proportional to the tissue thickness (T)
Vgas = (A/T) . D . (P1 – P2) |
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Term
| What does Fick's law explain? |
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Definition
the rapid diffusion of gases across the respiratory membrane
(large A and low T) |
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Term
| What does Fick's law highlight the importance in? |
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Definition
| maintaining a reasonably large partial pressure gradient (especially for O2, whose solubility is relatively low) |
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Term
| What happens to atmospheric air when it is inhaled, before it reaches the alveoli? (2) |
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Definition
1. mixed with air in the respiratory 'dead space' which is rich in CO2 and deficient in O2
2. becomes saturated with water vapour (PH2O = 47mmHg at 37dc) |
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Term
| What difference does this cause alveolar air to have to atmospheric air? |
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Definition
| higher PCO2 and Lower PO2 |
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Term
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Definition
PAO2 = 100mmHg
PACO2 = 40mmHg |
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Term
| Give atmospheric PO2 and PCO2 |
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Definition
PO2 = 160mmHg
PCO2 = 0.3mmHg |
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Term
| Give systemic PaO2 and PaCO2 |
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Definition
PaO2 = 100mmHg
PaCO2 = 40mmHg
These figures are the same for alveolar air, pulmonary veins and systemic arteries |
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Term
| Give pulmonary PaO2 and PaCO2 |
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Definition
PaO2 = 40mmHg
PaCO2 = 46mmHg
also true for systemic veins |
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Term
| Give a very basic pattern for PO2 and PCO2 in the body |
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Definition
PO2 decreases from atmospheric air to pulmonary arteries (120 drop overall)
PCO2 increase from atmospheric air to pulmonary arteries(45 increase overall) |
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Term
| Why does PCO2 only increase by 6mmHg from systemic arteries to pulmonary arteries? |
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Definition
| CO2 is about 20x more soluble than O2 |
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Term
| Explain the changes in PO2 as altitude above sea level rises |
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Definition
| PO2 decreases in proportion with the decrease in barometric pressure (PB) |
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Term
| How does the O2 diffusion gradient from atmosphere to alveoli to arterial blood to tissue change as altitude increases? |
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Definition
decreases
therefore sufficient o2 delivery is difficult
acclimatisation is needed |
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Term
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Definition
the amount of a gas that dissolves in a liquid at equilibrium depends on both the partial pressures of the gas in the gas mixture to which the liquid is exposed, and on the specific solubility of that gas in that particular liquid
c = kP |
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Term
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Definition
once a system (e.g. alveolar air and blood) has reached equilibrium, the partial pressures would have reached equilibrium, however the concentrations would be different.
At any given partial pressure, the conc of o2 in blood is much lower than the conc of co2. |
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Term
| Compare o2 and co2 solubility |
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Definition
| o2 is about 20 times less soluble than co2 |
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Term
| How does pressure change with water depth |
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Definition
| pressure increases so that even 10m adds 1 atmosphere (e.g. 760mmHg) of pressure |
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Term
| A diver at a depth of 30m is breathing a mixture of O2 and N2 at a pressure of ___ atm |
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Definition
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Term
| What are the corresponding partial pressures of o2 and n2 |
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Definition
o2 = 635mmHg
n2 = 2400mmHg |
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Term
| What does this mean for n2? |
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Definition
| 4x the amount of n2 dissolved in body fluids and tissues |
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Term
| What are the effects of a rapid ascent? |
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Definition
- sudden drop in PN2 in the lungs and body tissues
- n2 comes out of solution and forms bubbles
- severity depends on how many bubbles and if (and where) they become trapped |
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Term
| How long does it take for o2 and co2 to equilibriate when passing through a typical pulmonary capillary? |
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Definition
O2 equilibrates within the first third of the time it takes for blood to pass along a capillary.
0.25s (out of 0.75s) |
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Term
In a healthy individual, what is gas exchange in the lung limited by?
at rest!! |
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Definition
rate of pulmonary blood flow
perfusion limited |
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Term
| How does this change at exercise? |
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Definition
it doesn't
transit time is .25s so should still be perfusion-limited
diffusion still proceeds to equilibrium |
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Term
| How might this change is the blood-gas barrier is thickened by disease? |
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Definition
o2 uptake may become diffusion limited
especially during exercise |
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Term
| When might o2 uptake may become diffusion limited in healthy subjects? |
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Definition
| if PAO2 is reduced (e.g. at high altitude) |
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Term
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Definition
1. abnormally high rate of capillary fluid filtration
2. impaired lymphatic drainage |
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Term
| What causes pulmonary oedema? |
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Definition
left sided heart failure
causes increased pulmonary venous and capillary pressures leading to hydrostatic oedema |
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Term
| What two phases does pulmonary oedema occur in? |
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Definition
1. interstitial oedema - accumulation of excessive fluid in the interstitial spaces in the lung
2. alveolar oedema - fluid accumulates within the alveoli. |
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Term
| How does alveolar oedema interfere with breathing? |
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Definition
1. increases the effective thickness of respiratory membrane (increasing the air to blood diffusion distance)
2. interfering with the action of pulmonary surfactant, which decreases lung compliance and increases the work of breathing |
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Term
| Symptoms of pulmonary oedema |
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Definition
srapid shallow breathing
hypoxia
cyanosis |
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Term
| Describe Type I alveolar cells |
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Definition
| make up the wall of alveoli, comprised of a single layer of epithelial cells. |
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Term
| Describe Type II alveolar cells |
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Definition
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Term
| At what partial pressures does O2 and CO2 enter the systemic capillaries? |
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Definition
PO2 = 100mmHg
PCO2 = 40mmHg |
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Term
| What are the partial pressures of O2 and CO2 like in the surrounding ISF? |
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Definition
PO2 is lower
PCO2 is higher
(actual values depend on metabolic activity) |
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Term
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Definition
| O2 diffuses from the blood into the surrounding tissues and CO2 diffuses in the opposite direction |
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Term
| Compare the PO2 and PCO2 of arterial and venous blood |
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Definition
arterial has higher PO2 and lower PCO2
venous has lower PO2 and higher PCO2 |
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Term
| Describe the blood in systemic veins |
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Definition
blood may leave systemic capillary beds with different PO2 and PCO2 values and is mixed together in the systemic veins = mixed venous blood
PO2 of 40mmHg and PCO2 of 46mmHg |
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Term
| What 3 factors determine alveolar PO2 and PCO2 |
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Definition
1. PO2 and PCO2 of inspired air
2. volume of fresh air reaching the alveoli each minute (alveolar ventilation)
3. the rates at which respiring tissues consume o2 and produce co2 |
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Term
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Definition
alveolar ventilation relative to the rate of o2 consumption and co2 production
PO2 and PCO2 do not change under most conditions |
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Term
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Definition
An appropriate increase in alveolar ventilation relative to the demands of the tissue i.e. if o2 consumption and co2 production increase, do does alveolar ventilation
therefore, alveolar alveolar po2 and pco2 do not change |
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Term
| What happens when alveolar ventilation does no match the demands of the tissue? |
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Definition
| hyperventilation and hypoventilation |
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