Zoology Assignment Help >> Pulmonary Volumes

Pulmonary Volumes

Lungs at any time in life are neither completely filled nor evacuated. Different amount of air which comes in or goes out or remains in are variously termed as:

1. Tidal volume-{T.V.}-Maximal amount of air expired or inspired involuntarily. This is about 500 ml.

2. Inspiratory reserve volume (I.R.V.)-Maximal volume of air that can be inspired over and above the tidal volume by deepest voluntary lnsptration. This is about 2000 to 3500 ml.

3. Expiratory reserve volume (E.R.V.)-Amount of air that can be expired over and above the tidal volume by the most forceful voluntary expiration. This is about 1000 ml.

4. Residual volume-Volume of air that remains inside the lungs after a most forceful expiration. This is about 1500 ml.

5. Inspiratory capacity-T.V. + I.R.V. = I.C.

500 ml + 3000 (average) ml = 3500 ml

6. Functional residual capacity¬-E.R.V. + R.V. = F.R.C.

1000 ml + 1500 ml = 2500 ml

7. Vital capacity in man-I.R.V. + T.V. + E.R.V = V.C.

3000 ml + 500 ml + 1000 ml = 4500ml

8. Total lung capacity- T.V. + I.R.V. + E.R.V. + R.V. = T.L.C.

or V.C. + R.C.= T.L.C.

4500 ml + 1500 ml = 6000 ml

Dead space: Conducting passage to the lung alveoli where the trapped air does not take part in respiration or in simple words, this air does not reach alveoli and hence does not take part in respiration. This amount of air is called "dead volume" and this passage is called "dead space"

At N.T.P. air contains - Oxygen- 21%

Carbon dioxide - 0.04% Nitrogen - 78%

Water vapour - Changeable Inert gases - 1%

Oxygen present in the air in the body creates certain pressure in the air which is known as partial pressure of oxygen P_o2Similarly CO₂ also produces the partial pressure of CO₂ (PCO₂). The higher partial pressure P_co2 in the air causes the diffusion of the same gas into the blood for the combination with the blood component and the lower partial pressure of O2 causes the diffusion of the gas from the blood. Mainly O2 is transported by the haemoglobin as a chemical combination but very small amount of CO2 is also transported by the blood plasma as physical solution. But CO2 is mainly transported as bicabonates in physical solution. It is also carried as carbamino-haemoglobin in R.B.C. The combination of CO₂ with water forms the carbonic acid in the presence of carbonic anhydrase in A.B.C. but this carbonic acid forms the bicarbonates. Some of these bicarbonates also diffuse out of the R.B.C.

In alveolar air-

Tension of oxygen is about - 107 mm Hg

Tension of CO₂is about - 40 mm Hg

In venous blood-

Tension of oxygen is about - 40 mmHg

Tension of CO₂ is about - 46 Hg

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