This document summarizes key concepts about diffusion through the alveolar membrane and protective reflexes of the respiratory system. It discusses the principles of net diffusion, factors that affect diffusing capacity, and diffusion of oxygen and carbon dioxide through the membrane. It also explains three protective reflexes - the cough reflex, sneeze reflex, and Hering-Breuer inflation reflex. The cough reflex protects the lungs from foreign bodies through forced inspiration, glottis closure, abdominal/intercostal muscle contraction, and air expulsion. The sneeze reflex similarly protects the nasal passageway. The Hering-Breuer reflex prevents over-inflation of the lungs by inhibiting inspiration when stretch receptors are stimulated.

1. Diffusion Through Alveolar
Membrane
presented by AASMA MEHAK
presented to MISS KHADIJA
DPT SEM-II
KIHST

2. PRINCIPLES OF NET DIFFUSION
1. The partial pressure of a gas is greater in one area than in another area (pressure
gradients).
2. solubility of O2 should be constant (the rate of absorption of oxygen into the
blood).
3. The rate of entry of new oxygen into the lungs by Ventilation process
and rate of excretion of CO2 should be maintained.

3. DIFFUSING CAPACITY OF RESPIRATORY MEMBRANE.
The volume of the gas that will diffuse through the membrane each minute for the
partial pressure difference of 1mmHg.
1. DIFFUSING CAPACITY FOR OXYGEN.
Under resting conditions the diffusing capacity = 21ml/min/mmHg.
The mean difference across membrane during quiet breathing = 11mmHg.
Total diffusion across membrane in each minute = 230ml of O2(11x21).
During exercise the capacity = 65ml/min/mmHg. 2

4. 2. DIFFUSING CAPACITY OF CARBONDIOXIDE
The average Pco2 in the pulmonary blood is not far different from Pco2
in the alveoli because CO2 diffuses so rapidly through membrane.
The average difference is less than 1mmHg.
The diffusing capacity is 20 times more than oxygen.
Under resting conditions the capacity = 400 to 450ml/min/mmHg.
During exercise the capacity = 1200 to 1300ml/min/mmHg. 3

5. FACTOR AFFECTING DIFFUSING CAPACITY
a) Pressure gradient.
b) Solubility of gas in fluid (blood).
c) Total surface area of respiratory membrane.
d) Molecular weight of the gas.
e) Thickness of respiratory membrane.

6. DIFFUSION OF OXYGEN
a) DIFFUSION OF O2 FROM ATMOSPHERE TO ALVEOLI
Partial pressure of oxygen in atmospheric air is 150mmHg and in alveoli is
100mmHg.
The pressure gradient is 50mmHg.
oxygen easily enters from atmospheric air to alveoli.
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7. b) DIFFUSION OF O2 FROM ALVEOLI TO BLOOD
Partial pressure in pulmonary capillaries is 40mmHg and alveoli is 100mmHg.
The pressure gradient is 60mmHg. It facilitates diffusion of oxygen from alveoli
to blood (from high to low pressure).

8. DIFFUSION OF CARBON DIOXIDE
a) DIFFUSION OF CO2 FROM BLOOD TO ALVEOLI.
Partial pressure of carbon dioxide in alveoli is 40mmHg whereas in
blood the pressure is 46mmHg. The pressure gradient of 6mmHg
responsible for diffusion of CO2 from blood to alveoli.
b) DIFFUSION OF CO2 FROM ALVEOLI TO ATMOSPHERE.
The partial pressure of carbon dioxide in atmosphere is only about
0.3mmHg and in alveoli it is 40mmHg. So, the gas will diffuse to low
pressure gradient in atmosphere
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10. PROTECTIVE REFLEXES
PART-B
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11. INTRODUCTION
Protective reflex describes the reflexive withdrawal of the body or parts of
the body from either actual or perceived painful stimuli.
PROCTECTIVE REFLEXES OF RESPIRATORY SYSTEM.
a) cough reflex
b) sneeze reflex
c) Hering-Breuer reflex

12. COUGH REFLEX
Cough reflex is an expulsive reflex that protects the lungs and
passage from foreign body.
Causes of Cough.
a) Irritants, smokes, fumes any corrosive gas like sulphur dioxide & chlorine
gas.
b) Infections (bacterial infections like influenza).
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14. PHASES OF COUGH.
1. Forceful inspiration.
2. Closure of glottis.
3. Contraction of abdominal and
intercostal muscle and increase in
positive intercostal pressure.
4. Expulsion of air.
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15. SNEEZE REFLEX
The sneeze reflex is same as cough reflex , except that it applies to nasal
passageway instead of lower respiratory passages.
It is also caused by stimulus that irritating to nasal cavity.

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18. HERING-BREUER INFLATION REFLEX
The Hering–Breuer inflation reflex, is a reflex triggered to prevent over-
inflation of the lung.
When the lungs are inflated, the receptors (stretch) are stimulated and these
impulses are carried by vagus nerve.
Impulses ultimately cause inhibition of inspiratory center so that inspiration
stops and expiration starts.
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