What microscopic functional unit within the human lungs is the primary site of respiratory gas exchange between inhaled air and the bloodstream?
Answer and explanation
Correct answer: B. Alveoli
- Step 1: The human respiratory tree terminates in clusters of tiny, thin-walled microscopic air sacs called alveoli, totaling roughly 300 to 500 million in adult lungs.
- Step 2: Lined by single-layered squamous epithelium and enveloped by dense capillary beds, alveoli provide an immense surface area (about 70 square meters) for the diffusion of oxygen and carbon dioxide.
Answer
Alveoli
Why not the others: 'Bronchioles' Bronchioles are small conducting airways that channel air into the respiratory zones, but lack thin diffusion walls for gas exchange; 'Trachea' The trachea (windpipe) is a cartilaginous conducting airway leading from the larynx to the main bronchi; 'Pleura' The pleura is a double-layered serous membrane enclosing and lubricating the lungs within the pleural cavity.
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