Gas Pressure Gas pressure is caused by the molecules colliding with the surface In the lungs the gas molecules are colliding with the surfaces of the respiratory passages and alveoli Higher concentrations of gas will produce more collisions and cause a higher pressure ID: 643964
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Slide1
Gas Exchange and Pulmonary CirculationSlide2
Gas Pressure
Gas pressure is caused by the molecules colliding with the surface.
In the lungs, the gas molecules are colliding with the surfaces of the respiratory passages and alveoli.
Higher concentrations of gas will produce more collisions and cause a higher pressure.
This idea of pressure applies to gases whether in air or water.Slide3
Diffusion
Gases diffuse from an area of high concentration to an area of low concentration.
It is based on the probability of freely moving molecules.Slide4
Direction of Diffusion
The net diffusion is determined by the difference between the partial pressures.
If the partial pressure of O
2
is greater in the alveolar air than in the blood, the net diffusion of O
2
will be
into
the blood.Slide5
Diffusing Capacity
Diffusing capacity is a measure of how well as gas diffuses across the respiratory membrane.
It is defined as the volume of a gas that will diffuse through the membrane each minute for a partial pressure difference of 1 mm Hg.Slide6
Diffusing Capacity for O2
Diffusing capacity for O
2
is ~ 21 ml/min/mm Hg in the average young man.
Multiply this by the mean pressure difference (11 mm Hg) and one obtains the amount of O
2
diffusing through the respiratory membrane each minute. In this example, 230 ml O
2
/min.Slide7
Dalton’s Law of Partial Pressure
The total gas pressure is the pressure caused by all the gas molecules colliding with the surface.
The partial gas pressure is the pressure exerted by 1 gas species alone. Written as P
O2
(partial pressure of O
2
), P
CO2
(partial pressure of CO
2
).
Atmospheric Air Partial Pressures
The rate of diffusion of a gas molecule is directly proportional to its partial pressure.
Nitrogen
597 mm Hg
78.62 %
Oxygen
159 mm Hg
20.84 %
Carbon Dioxide
0.3 mm Hg
0.04 %
Water
3.7 mm Hg
0.5 %
Total
760 mm Hg
100 %Slide8
Henry’s Law
When a mixture of gasses is in contact with a liquid each gas will dissolve in the liquid in proportion to its partial pressure.Slide9
Solubility Coefficient
The higher the solubility, the higher the solubility coefficient and the lower the partial pressure for a given concentration.Slide10
Comparing Atmospheric and Alveolar Air
In the alveoli:
O
2
is constantly being absorbed into the blood.
CO
2
is diffusing into the alveolar air.
Air is humidified compared to atmospheric air.Slide11
Rate of Alveolar Removal
The alveolar air is replaced slowly. During normal ventilation, ~1/2 of the gas is removed in 17 sec.
The slow replacement of alveolar air prevents sudden changes in [blood gas].Slide12
Partial Pressure of O
2
in Alveoli
Alveolar P
O2
depends on:
- The rate of O
2
absorption into the blood.
- The rate of entry of new O
2
during ventilation.
Why does the alveolar partial pressure of O
2
not increase above 150 mm Hg?Slide13
Partial Pressure of CO
2
in Alveoli
Alveolar
P
CO2
depends on:
- The rate of CO
2
excretion from the blood.
- The rate of removal of CO
2
during ventilation.
Slide14
Respiratory Membrane
Gas exchange between the alveolar air and pulmonary blood occurs through the alveolar ducts and alveoli.
For gas exchange to be efficient their must be a match between the amount of gas reaching the alveoli (ventilation) and the blood flow in the capillaries (perfusion). Slide15
Respiratory Membrane
In healthy lungs the alveolar membrane and the capillary wall are only about 1 cell thick, so gas exchange can occur easily.Slide16
Factors Affecting Diffusion through the Respiratory Membrane
Thickness of the membrane.
Surface area of the membrane.
Diffusion coefficient.
Difference in partial pressure.Slide17
Hemoglobin
Remember that O
2
from the lungs is carried by red blood cells.
On every red blood cell is an iron containing
heme
group.
Each hemoglobin molecule can bind with 4 molecules of O
2Slide18
Hemoglobin
A hemoglobin with an oxygen is called an
oxyhemoglobin
. (HbO
2
)
A hemoglobin that has released it’s oxygen is called a reduced or
deoxyhemoglobin
. (
HHb
)Slide19
Hemoglobin
The rate at which
Hb
binds or releases O
2
is regulated
by the following:
Partial Pressure
Temperature
Blood pH
Concentration of organic ChemicalsSlide20
CO2
Transport
A normal body cell produces 200 ml of carbon dioxide each minute.
Blood transports CO
2
from the tissues to the lungs in three forms
Dissolved in the plasma (7-10%)
Bound to hemoglobin (roughly 20%)
As a bicarbonate ion in plasma (70%)Slide21
From CO2
to Bicarbonate
CO
2
enters the plasma and then enters the RBC to be turned into Bicarbonate.
When CO
2
enters the blood cell it combine with water to make carbonic acid.
Carbonic acid is unstable and quickly disassociates into hydrogen ions and bicarbonate.Slide22Slide23
The Bohr Effect
When the Hydrogen ions are released they bind with
Hb
(hemoglobin) and cause the release of O
2.
The Bicarbonate is released back into the plasma and carried to the lungs.Slide24
From Bicarbonate to CO2
Once in the lungs the Bicarbonate returns to the RBC and the whole process is reversed producing CO
2,
which you exhale.Slide25Slide26
Buffer System
The process of turning carbonic acid into bicarbonate and visa versa is how your body deals with pH shifts.
If too many H
+
are present bicarbonate in the plasma will bond with it forming carbonic acid.
If H
+
are too low then carbonic acid will disassociate and release the hydrogen ions.Slide27
Acidosis/Alkalosis
Too much CO
2
in the blood will result in more carbonic acid and there fore a lower pH level.
If prolonged this will cause acidosis and organ failure can occur.
Not enough CO
2
and the blood pH will rise causing Alkalosis.