Pulmonary acinus

Pulmonary Acinus

The Pulmonary Acinus is a functional unit of the lung, which is the primary organ of respiration in humans and most other mammals. The term "acinus" is derived from the Latin word for "grape," reflecting the grape-like clusters of alveoli at the end of the terminal bronchioles that constitute the acinus.

Structure

Each pulmonary acinus is composed of a terminal bronchiole, the smallest airway of the lung, and the alveoli that it supplies. The terminal bronchiole divides into several respiratory bronchioles, each of which further divides into alveolar ducts. These ducts end in alveolar sacs, clusters of alveoli that resemble a bunch of grapes.

Function

The primary function of the pulmonary acinus is gas exchange. Oxygen from the inhaled air diffuses across the thin walls of the alveoli into the surrounding capillaries, where it binds to hemoglobin in red blood cells. At the same time, carbon dioxide, a waste product of cellular metabolism, diffuses from the blood into the alveoli and is exhaled.

Clinical Significance

Diseases that affect the pulmonary acinus can severely impair gas exchange and lead to respiratory failure. These include emphysema, a condition characterized by destruction of the alveoli, and pneumonia, an infection that inflames the alveoli and fills them with fluid.

See Also

• Respiratory System
• Alveoli
• Bronchiole
• Pneumonia
• Emphysema