L10 Flashcards
Fick’s Law States:
Thus:
Amount moved =
“The amount of a substance moving from one region to another depends on the area available for diffusion, the concentration gradient, and a constant known as the diffusion coefficient”.
Thus:
Amount moved = area X concentration gradient x diffusion coefficient
Przypomnienie: Fick’s Law of diffusion eq negative sign
The negative sign indicates that diffusion occurs from a region of high to a region of low concentration. Thus the diffusion coefficient becomes smaller as the molecular size
increases so that large molecules diffuse more slowly than small ones.
It is measured by its diffusion capacity:
The ability of the lungs to ensure equilibration between the blood in the pulmonary capillaries and the alveolar air is measured by its diffusion capacity.
The diffusion capacity -
the volume of gas that diffuses through alveolar membranes per time for a given partial pressure difference.
Diffusion capacity =
volume of gas diffusing between the alveoli and blood
partial pressure in alveolar air – partial pressure in pulmonary capillaries
To estimate diffusion capacity we use … as in alveolar capillaries this will be … as it binds so strongly to …
+ poprawa równania diffusion capacity
Carbon monoxide ;zero ;HB
.Thus:
Diffusion capacity = volume of CO / partial pressure in the alveoli of CO
In a normal health individual diffusion capacity for CO
measured by the single-breath method give values of :
225ml min-1 kPa-1 or 30ml min-1 mmHg-1 at rest.
The diffusion capacity for Oxygen = 1
The diffusion capacity for CO2 = 2, as it is …
CO X 1.23
O2 X 20, much more soluble in alveolar membranes.
Movement of CO2 and O2 depend on: (3)
- Pressure Gradients
- The Diffusion Coefficient
- Tissue Properties
Henry’s Law states:
equilibrium Amount dissolved-
“At equilibrium, the amount of gas dissolved in a liquid with which it does not chemically combine is proportional to the partial pressure of the gas to which it is exposed”.
V = sP
Amount dissolved = solubility coefficient x Partial Pressure of the gas
O2 content in arterial blood-1.
O2 content in venous blood-2.
CO2content in arterial blood-3.
CO2content in venous blood-4.
- 20ml per 100ml (1dL)
- 15ml per 100ml (1dL)
- 48ml per 100ml (1dL)
- 52ml per 100ml (1dL)
Usually you release … of CO2 for every … of O2 taken up,
this is referred to as the “…”. Ideally …
4ml
5ml
respiratory exchange ratio
0.8.
FRACTIONAL CONCENTRATION (F) -
thus:
FO2=
FN2=
Denotes the relative quantities of gases in any mixture;
thus:
FO2 is 0.21 (as there is 21% in dry air), or FN2 is 0.79.
Partial pressure =
Total Pressurex Fractional Conc.
e.g. PO2 = 101kPa (760mmHg) x 0.21 = 21.2kPa (160mmHg)
Gas exchange depends on: (3)
• The partial pressure gradients between alveolar
air and pulmonary blood for both O2 and CO2
• Easy diffusion between the alveoli and blood
• Appropriate balance between ventilation and
perfusion
The flow of blood to different parts of the lung is determined by three pressures:
• The hydrostatic pressure in the pulmonary arteries
in different parts of the lung
• The pressure in the pulmonary veins
• The pressure of the air in the alveoli.
przypomnienie…
BLOOD FLOW THROUGH THE UPRIGHT LUNG IS
GREATEST AT THE BASE AND LEAST AT THE
APEX.
The respiratory system can be considered to consist of two parts:
Conducting airways
Area of gas exchange
Not all the air taken in in one breath reaches the
alveolar surface, some must occupy the airways
that connect the respiratory surface to the
atmosphere. This air is known as anatomical ….
dead space
The determination of physiological dead space
can be carried out using … rather than… .
CO2 and O2
N2
As the concentration of CO2 is almost zero in inspired air then the CO2 breathed out will
eventually give us the concentration in alveolar air.
If an area of the lung is perfused but inadequately ventilated, Va/Q will be ….. As a result the alveolar PO2 … and PCO2…. as less fresh air is brought into the alveoli.
reduced, falls, rises
If Va/Q =0 there is ……
, as PO2 ….. there will be more
shunting of blood away from those areas of the lungs as seen in …..
perfusion and no ventilation, falls, respiratory disease.
If the alveoli are ventilated but inadequately perfused, Va/Q will be ….. As a result the alveolar PO2 ….and PCO2 …
increased, rises, falls.
If pulmonary flow = 0 there is ….. and alveolar pressure and that of humidified room air become equal as seen in …..
no perfusion with ventilation, pulmonary embolism.
(Poiseuille’s Law)
R = ΔP / V
where R is the airway resistance; ΔP is the difference in pressure between atmospheric and the alveoli and V is the airflow.
