NEET Practice Questions (MCQs) with Answers & Solutions

During expiration, the diaphragm relaxes. When the diaphragm relaxes, it moves back to its dome-shaped position, which decreases the volume of the thoracic cavity and increases the pressure, causing air to be expelled from the lungs.

Carbon dioxide is transported from the tissues to the respiratory surface primarily by plasma and erythrocytes. In erythrocytes, CO2 combines with water to form bicarbonate, which is then transported in the plasma. This process helps to maintain acid-base balance in the body.

The respiratory center is located in the medulla oblongata, which is part of the brainstem. This center controls the rate and depth of breathing by sending signals to the respiratory muscles. The medulla oblongata has two main areas involved in respiration: the dorsal respiratory group (DRG) and the ventral respiratory group (VRG).

The correct pathway for air to reach the lungs is: Nostrils → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli. This sequence ensures that the air is properly filtered, warmed, and humidified before reaching the delicate alveolar sacs where gas exchange occurs.

The volume of air breathed in and out during effortless respiration is known as the tidal volume. It represents the normal amount of air exchanged with each breath without any extra effort. For a healthy adult, the tidal volume typically ranges from 500 to 600 milliliters.

At high altitudes, the oxygen levels are lower. To compensate for the reduced oxygen availability, the body increases the number of red blood cells (RBCs) to enhance the oxygen-carrying capacity of the blood. This process is called erythropoiesis and is stimulated by the hormone erythropoietin.

The maximum amount (70-75%) of carbon dioxide is transported in the blood in the form of bicarbonate ions (HCO3-). When CO2 enters the red blood cells, it reacts with water to form carbonic acid (H2CO3), which quickly dissociates into bicarbonate and hydrogen ions. This reaction is catalyzed by the enzyme carbonic anhydrase.

Oxygen is primarily transported in the blood bound to hemoglobin in red blood cells (RBCs). Carbon dioxide is transported in the blood in three forms: dissolved in plasma, as bicarbonate ions, and bound to hemoglobin (carbaminohemoglobin). Therefore, both oxygen and carbon dioxide are transported through RBCs and plasma.

Tidal volume is the amount of air that is inhaled or exhaled during normal, relaxed breathing. It has the lowest value compared to other respiratory volumes like vital capacity, inspiratory reserve volume, and expiratory reserve volume. Vital capacity is the maximum amount of air a person can expel from the lungs after a maximum inhalation, and both inspiratory and expiratory reserve volumes are additional volumes of air that can be inhaled or exhaled beyond the normal tidal volume.