Breathing Mechanics: Pressure Gradients — NEET Biology
📚 Practice ConceptBreathing involves two stages: inspiration during which atmospheric air is drawn in and expiration by which the alveolar air is released out. The movement of air into and out of the lungs is carried out by creating a pressure gradient between the lungs and the atmosphere. Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure, i.e., there is a negative pressure in the lungs with respect to atmospheric pressure. Similarly, expiration takes place when the intra-pulmonary pressure is higher than the atmospheric pressure. The diaphragm and a specialised set of muscles – external and internal intercostals between the ribs, help in generation of such gradients. Inspiration is initiated by the contraction of diaphragm which increases the volume of thoracic chamber in the antero-posterior axis. The contraction of external inter-costal muscles lifts up the ribs and the
Which of the following statements accurately describe the mechanism of breathing? S1: Contraction of the diaphragm initiates inspiration by increasing the volume of the thoracic chamber in the antero-posterior axis. S2: The external inter-costal muscles contract to lift the ribs and sternum, thereby increasing thoracic volume along the dorso-ventral axis. S3: An overall increase in thoracic volume directly leads to an increase in intra-pulmonary pressure, forcing air inwards. S4: Normal expiration is a passive process primarily involving the relaxation of the diaphragm and inter-costal muscles, reducing thoracic volume. S5: During forceful expiration, the active contraction of abdominal muscles further increases thoracic volume for greater air expulsion.
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