Question

In the given mechanism, diaphragm/ sternum and intercostal muscles work together to ______ the thoracic volume and thereby pulmonary volume; This leads to _______ in intrapulmonary pressure to slightly ______ the atmospheric pressure, causing expiration.
Select the correct sequence of words to complete the above paragraph.
A. Decrease, decrease, below
B. Increase, decrease, above
C. Decrease, increase, above
D. Increase, increase, below

Answer 1

The biological system consisting of specific organs and structures used for gas exchange in animals and plants is called the respiratory system. Exchange of gases in humans and reptiles occurs in the millions of small air sacs called alveoli in the lungs but atria in the birds. The rich blood supply in the microscopic air sacs brings the air in close contact with the blood. Through the system of airways, the communication between the external environment and the air sacs occurs at hollow tubes which the trachea is the largest that branches in the middle entering the lungs passing to secondary and tertiary bronchioles present in the numerous smaller tubes.

Complete answer: Inhalation of air at rest is primarily due to diaphragm contraction in mammals. The upgraded domes sheet of muscles separates with the thoracic and abdominal cavity. During the contraction, the sheet flattens by increasing the volume of the thoracic cavity. Diaphragm contraction pushes the abdominal organs downwards. The ribcage is simultaneously enlarged by the intercostal muscles that are pulled upwards.
The lowermost ribs slant downwards from the midline outwards but the ribs slant downwards from the rear to the front. Thus the rib cage's transverse diameter can be increased in the same way as the anteroposterior diameter is increased by the so-called pump handle movement.
By their anatomical elasticity chest and abdomen are determined to the position. This is the "resting mid-position" of the thorax and abdomen when the lungs contain their functional residual capacity of the air.
Hence, the correct option is (C) Decrease, increase, above.

Note: The primary purpose of the respiratory system is the equilibration of the partial pressures of the respiratory gases in the alveolar air with those in the pulmonary capillary blood. This process occurs by simple diffusion, across a very thin membrane, which forms the walls of the pulmonary alveoli. Alveolar epithelial cells, their basement membranes, and the endothelial cells of the alveolar capillaries are used in the functioning process.