Question

Lungs are made up of air-filled sacs, the alveoli. They do not collapse even after forceful expiration, because of
A. Expiratory Reserve Volume
B. Residual Volume
C. Inspiratory Reserve Volume
D. Tidal Volume

Answer 1

Hint: A pair of lungs is present in humans, lying in an air-tight chamber known as thoracic cavity or chest cavity. This cavity is formed dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs. It is closed below by the diaphragm which is a dome-shaped structure made up of muscles and separates the thoracic cavity from abdominal cavity.

Complete answer:
We have the ability to increase the strength of expiration. It is due to contraction of internal intercostal and abdominal muscles.
> Internal intercostal muscles : Contraction of these muscles leads to the pulling of ribs downward and inward, decreasing the volume of thoracic cavity.
> Abdominal muscles : Abdominal muscles contract thereby compress the abdomen and push its contents towards the diaphragm.
Now let us gather information about given options :-
> Expiratory Reserve Volume :- It is defined as the additional or extra volume of air, a person can expire by forceful expiration. This volume averages 1000 ml to 1100 ml.
> Residual Volume :- The volume of air which remains in the lungs even after the forceful expiration is termed as residual volume. It is about 1100 ml to 1200 ml. It prevents the lungs from collapsing.
> Inspiratory Reserve Volume :- It is defined as the additional or extra volume of air, a person can inspire by forceful inspiration. This volume averages 2500 ml to 3000 ml.
> Tidal Volume :- During normal breathing, the volume of air inspired or expired is known as tidal volume. Its value is approximately 500 ml. If we take the case of a healthy man, he can inspire or expire approx. 6000 ml to 8000 ml of air/min. But in a diseased person suffering from any kind of pulmonary problems, its value will be altered. Value of tidal volume is the lowest among all types of respiratory volumes.

Our required option is B that is residual volume.

Note:
After forceful expiration , residual volume helps to prevent lungs from collapsing. It gives a time lack between oxygen to be absorbed and carbon dioxide to be removed. The rate of breathing in a normal healthy man is 12-16 times/min . Respiratory volume is defined as the quantity of air which lungs can hold under different conditions.