Question

M3 Discussion: The Respiratory System

This is something of a different type of discussion. Discuss in 1-2 short paragraphs 2 of the most informative pieces of information you learned in this chapter. You can discuss one of the homeostatic imbalances, a fundamental principle of respiratory capacities, gas exchange, etc, anything that was presented in the chapter you particuarly are interested in.

Answer 1

GAS EXCHANGE:

Sites of Gas exchange:

*At tissues(between blood and tissues)

*At the lungs(between blood and air)

Mechanism of Gas exchange

*Simple diffusion: Down partial pressure gradient from high to low partial pressure

In the lungs:

*Venous blood enters pulmonary capillaries( High pco2 & Low po2).

*Air enters alveoli(High po2 & Low pCo2).

•O₂ diffuses from alveoli to blood down its pressure gradient.

•CO₂ diffuses from blood to alveoli down its pressure gradient.

Factors affecting gas diffusion

1) Partial pressure gradient of the gas across the alveolar capillary membrane.(60 mmHg for O₂ & 6mmHg for CO₂).

2)Surface area of the alveolar capillary membrane (about 70m²).

3) Thickness of the alveolar capillary membrane (about 0.5microns).

4) Diffusion coefficient of the gas depends on :

• Gas solubility : (CO₂ is 24 times soluble than O_{​​​​​​2).}

_{• Molecular weight of the gas.(CO2 M.W. is 1.4 times greater than O2)}

_{• Net effect : CO2 diffusion is 20 times aster than O2}

^{​​​​​​​Rate of gas diffusion=}

^{Diffusion coefficient*Pressure gradient*Surface area of membrane​​​​​​}

1. thickness of the membrane

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•The volume of the gas transfer across the alveolar capillary membrane per unit time is :

Directly proportional ​​​​to:

* The difference in the partial pressure of gas between alveoli and capillary blood.

*The Surface area of the membrane

*The solubility of the gas.

Inversely proportional to:

* Thickness of the membrane

* Molecular weight of the gas.

The diffusion capacity of the respiratory membrane: The volume of gas that diffuses across the alveolar capillary membrane /min for a pressure difference of 1mmHg.

=20ml/min./mmHg for O2

=400ml/min/mmHg for CO2

Diffusion capacity increases during exercise:

80ml/min/mmHg forO2

1600ml/min/mmHg for CO2CO2

Diffusion capacity decreases in:

•conditions that increases alveolar -capillary membrane thickness

• conditions that decreases the effective area for diffusion.

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