Flashcards in L9 Diffusive Gaseous Exchange Deck (26):

1

## Gaseous diffusion

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Inhalation --> Excretion

Atmosphere -tidal volume-> Lung -gaseous exchange-> Circulation -gaseous exchange-> cell --> circulation --> Lung --> Atmosphere

-Diffusion drives the gas into the Mitochondria in the cell

-Diffusion: therefore entirely passive (no active transport) driven by difference in partial pressure

2

## Driver of Gaseous diffusion

### Gaseous diffusion of gas is driven by a difference of Partial pressure of the gas

3

## Gaseous Diffusion

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The partial pressure (P) of a dissolved (into the blood) gas

-the pressure required to prevent a gas from diffusing out of the solution is its partial pressure

-Soluble gas in solvent, molecules with upwards random motion. Weightless barrier/plunger. Downwards Force to overcome the escaping force of the molecules.

Pressure= Force spread over the area = F/A

-Partial pressure of a gas in solution has the same magnitude as the partial pressure of the gas in the air with which it is in equilibrium

4

## Partial pressure

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Dalton's Law

PARTIAL because the barometric pressure is the sum of the different pressures of different elements

PB = PN2 + PAr + PO2 + PH2O + ...

PN2= 78%

PO2= 21%

PCO2= little bit

PH2O= varies greatly

5

## Partial pressure of gas in solution

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The Partial pressure of a gas in solution has the same magnitude as the partial pressure of the gas in the air with which it is in equilibrium

(gas Partial pressure solution = /same as equilibrium air)

-if oxyHb is in equilibrium with oxygen in air, partial pressure of Oxygen will be 21%

(never truely 21% as there is alot of loss of partial pressure throughout the system)

6

## Gaseous diffusion equilibrium

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solution with solvent with gas dissolved in it. partial pressure in solution in equilibrium with partial pressure of gas above

-->

Removing air on top, place plunger on, and stopping the molecules from escaping with force applied on plunger

7

## Gas Solubility

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the AMOUNT of gas dissolved per unit of volume per unit of PARTIAL PRESSURE

sigma = C (content) / P (partial pressure)= axis

=HENRY's Law

=molL-1 / kPA = mLL-1/mmHg

-increase partial pressure of gas in solution, will increase the content of that gas

-High solubility= for any given partial pressure, we will get more of that gas dissolved than if low solubility

-gradient= solubility

8

## Oxygen and CO2 Solubility

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High solubility= CO2 = 60mLL-1 (100mmHg)-1

Low Solubility= O2 = 3mLL-1 (100mmHg)-1

(per L of blood)

-CO2 is 20x more soluble in blood vs oxygen

(100mmHg is the partial pressure of O2 in blood (vs 21% partial pressure in air). for Barometric pressure of 760mmHg, 150mmHg partial pressure of O2 in room vs 100mmHg in lung))

-units: mLL-1 (mmHg)-1

9

## Diffusion of Oxygen across the alveolar membrane

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V.O2= rate of oxygen consumption = Volume O2/ delta(t) = VO2/delta(t)

=consumption creates the partial pressure gradient for diffusion to occur

-must be oxygen being consumed in capillaries

-consumption decreases the partial pressure, allowing gradient to be established

-V.O2 commonly measured at mouth

10

## Diffusion of Oxygen across the alveolar membrane equation

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VO2/delta(t) = V.O2 = D(o2) x A x ((solubility o2) x (PAo2 - PCo2))/d)

D= diffusivity = inherent property of oxygen/ability to diffuse (different for every gas)

A= area of pulmonary membranes available for exchange

sigma= Solubility (if insoluble then nothing will go across)

(PAo2-PcO2) = partial pressure gradient = driving force

d= thickness= diffusion is inversely proportional

V.O2 = D(L) (PAo2 - Pco2)

where D(L) = Dgas x Solubility gas x (A/d)

-only thing that matters is the partial pressure gradient (higher is being delivered through cylinder)

-D(L) = Diffusing capacity of the lung= new constant combining the previous multiple constants

-Dgas and Solubilitygas = both different for every gas = both aid diffusion and help to overcome oxygens low solubility

-A and d will characteristic of the lung itself (A=100m2 (huge)) (d=300nm (very small))

11

## D(L)

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Diffusing capacity of the lung

Diffusive conductance of the lung

-conductance (quantity/time)

12

## Effect of diffusion distance on diffusion time

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distance something can diffusion depends on the SQUARE ROOT of time

(very slow process if distance is large)

13

## Diffusion of O2 through protoplasm

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-diffusion in terms of vessels

diffusivity= time to reach 90% saturation at centre of cylinder (from outside)

1cm= Low gradient as large distance = takes 11100 sec

7mm= steeper gradient = takes 54sec (nearly 1min)

7um= very steep gradient = 0.0054s

-diffusion is very fast over small distances, and very slow over large distances. due to square root relationship

14

## Delivery of O2 to cell masses

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-diffusion in terms of tissue

Diffusion: collection on cells relying on external diffusion = low gradient and low time to reach 90% equilibrium

Circulation= BV circulation around each cell= vastly reduce diffusion distance = reduce diffusion time

-Striated muscle= supply every cell with a supply of Oxygen

-diffusion is very fast over small distances, and very slow over large distances. due to square root relationship

15

## Ways to decrease diffusion distance

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1. Decrease vessel diameter

2. Circulation around every cell (instead of having external diffusion)

16

## Measurement of the Diffusion capacity equation

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D(L(o2)) = rate of O2 pre unit time/ partial pressure gradient = V.O2/ (PAo2-PcO2)

O2 Proxy= D(L(CO)) = V.CO / PAco

17

## Diffusion and disease

### diffusion capacity is greatly reduced in many diseases

18

## Measurement of the Diffusion capacity

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CO is commonly used

1. Mimic's Oxygen in its (low) solubility (proxy for oxygen)

2. CO + Hb --> HbCO

-Co binds with Hb with great avidity

-binds and stays bound to Hb until RBC is recycled in a few months

-bound but doesnt release into cell= therefore PcCO approx 0 (doesnt re-circulate)

irreversibly taken up to the Hb

hence:

D(L(CO)) = V.CO / PAco

19

## Diffusion Limitation vs Perfusion Limitation

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Time gas/Hb/CO spends in capillary = 0.75 sec (3/4)

-rate increases with exercise

PO2 start of capillary= 40mmHG = mixed blood from all over body (some low some high in PO2)

resting= send blood out saturate --> comes back only 1/2 saturated = allows for reservoir to tap into during exercise

-semi wasteful as sending O2 out and bringing 1/2 back

20

## Diffusion Limitation vs Perfusion Limitation in disease

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Abnormal O2 diffusion

- RBC wont be full saturated by the time (0.75 sec) it leaves the capillary

-early in line= death

21

## Diffusion Limitation vs Perfusion Limitation Nitrous Oxide and CO

###
N2O= Nitrous oxide

fully saturated before even part way through the capillary (less than 0.25 sec)

CO= content stays very low as isnt be recirculated back/remains bound/irreversibly taken up to the Hb

22

## Steady state/Rest Gas Exchange: e.g. O2

###
Mitochondria consumes oxygen in cell = decreases O2 partial pressure = driving gradient for consumption

1. Ventilation= Advection= bulk movement of gases = (V.O2= V.IO2 - V.EO2) (rate of oxygen consumption= difference between rate of inspiring and expiring Oxygen (reserve left over)

2. Diffusion (across alveolar-pulmonary capillary membrane) = V.O2= DL (PAo2 - Pco2)

3. Advection of O2 in blood (Circulation) (bulk carrying of O2 in fluid/blood)

=Ficks Law = V.O2 = Q (Cao2 - C-vo2) = rate O2 leaves blood = CO/Rate of flow of blood x (difference in O2 content (systemic arterial-mixed venous blood)

(rest= 40% of blood comes back without being used)

4. Diffusion of O2 into cell/mitochondria = V.O2 = Dt (PcO2-PtO2)

=amount of oxygen per unit time disapearing into cells that is entering the mouth from atmosphere (stead state)

23

## Steady state

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at rest

-different to exercise where Left hand side of equation will change as consuming/using more oxygen per unit time

24

## Oxygen reservoir at rest

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3. Advection of O2 in blood (Circulation) (bulk carrying of O2 in fluid/blood)

=Ficks Law = V.O2 = Q (Cao2 - C-vo2) = rate O2 leaves blood = CO/Rate of flow of blood x (difference in O2 content (systemic arterial-mixed venous blood)

(rest= 40% of blood comes back without being used)

-maintain ability to lower amount of O2 reservoir during exercise

-if lower and keep everything else then V.O2 will increase

25

## Diffusion of O2 into cell/mitochondria

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4. Diffusion of O2 into cell/mitochondria = V.O2 = Dt (PcO2-PtO2)

=amount of oxygen per unit time disappearing into cells that is entering the mouth from atmosphere (stead state)

Dt= diffusing capacity of the tissues

PcO2= partial pressure of systemic capillaries (different capillaries)

PtO2 = partial pressure of tissues

-mitochondria can continue consuming O2 until 1 mmHg or lower

-therefore the partial pressure gradient can be very steep

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