Final answer:
The point where inspired gas reaches BTPS is called the alveolar point. This occurs during external respiration in the alveoli of the lungs, where gas exchange with the blood occurs. The residual volume helps to prevent the alveoli from collapsing.
Step-by-step explanation:
The name of the point where inspired gas achieves Body Temperature and Pressure saturation (BTPS) is known as the alveolar point. BTPS is a condition where the inhaled gas has been warmed to body temperature (37ºC) and fully saturated with water vapor in the respiratory tract and then reaches the alveoli, which are the primary site for gas exchange in the lungs. This process occurs during external respiration, which is the exchange of gases between the air in the alveoli and the blood in the pulmonary capillaries. The alveoli are crucial structures within the lung tissue that prevent the lungs from collapsing, due in part to the presence of a residual volume, which is the amount of air remaining in the lungs after a forceful exhalation. Furthermore, alveolar ducts connect to alveolar sacs where the gas exchange occurs, and this exchange is essential for maintaining the proper levels of oxygen and carbon dioxide in the blood.