Question
Select the correct events that occur during inspiration. [NEET (Sep.) 2020]
I. Contraction of diaphragm.
II. Contraction of external inter-costal muscles.
III. Pulmonary volume decreases.
IV. Intra pulmonary pressure increases.
(a) III and IV
(b) I, II and IV
(c) Only IV
(d) I and II
Answer/Explanation
Ans. (d)
Statement I and II are correct as during inspiration, the contraction of diaphragm occurs which pulls it downward, while the external intercostal muscles contract and lifts up the ribs and sternum. This increases the size of the thoracic cavity and decreases the pressure inside. As a result, air rushes in and fills the lungs.
Statement III and IV are incorrect because during inspiration, the volume of the thoracic cavity increases. This causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intrapulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs.
Question
Select the correct statement. [NEET (Odisha) 2019]
(a) Expiration occurs due to external intercostal muscles
(b) Intrapulmonary pressure is lower than the atmospheric pressure during inspiration
(c) Inspiration occurs when atmospheric pressure is less than intrapulmonary pressure
(d) Expiration is initiated due to contraction of diaphragm
Answer/Explanation
Ans. (b)
Statement (b) is correct as intrapulmonary pressure is lower than the atmospheric pressure during inspiration. Other statements can be corrected as
(a) Inspiration occurs due to external intercoastal muscles.
(c) Inspiration occurs when atmospheric pressure is more than intrapulmonary pressure.
(d) Inspiration is initiated due to contraction of diaphragm.
Question
Air is breathed through [CBSE AIPMT 1994]
(a) trachea-lungs-larynx-pharynxalveoli
(b) nose-larynx-pharynx-bronchusalveoli-bronchioles
(c) nostrils-pharynx-larynx-tracheabronchi-bronchioles-alveoli
(d) nose-mouth-lungs
Answer/Explanation
Ans. (c)
In mammalian respiratory system, air is breathed through nostrils, from nostrils air passes through pharynx (common passage for food and air) $\rightarrow$ laryn $x$ (voice box) $\rightarrow$ trachea (wind pipe) $\rightarrow$ bronchi ( 2 for each side lungs) $\rightarrow$ bronchioles $\rightarrow$ alveoli (small sacs or pouches for exchange of gases).