TERMINAL RESPIRATORY UNIT

                                                     TERMINAL RESPIRATORY UNIT 

It consists of all alveolar ducts and all of the accompanying alveoli that stem from the proximal respiratory bronchiole.

In human, one unit contains approximately 100 alveolar ducts and 2000 alveoli. It measures about 5mm diameter and 0.02ml volume at FRC. An acinus contains 10-12 Terminal Respiratory Unit(TRU). 

The gas exchange amongst the structures in TRU occurs more rapidly. All parts of the TRU participate in volume changes in respiration.

Alveoli is a complex structure with flat walls and sharp curvature at the junctions between the walls. The wall of the alveoli are predominately made of pulmonary capillaries.

 The inner lining of the alveoli are made up of cuboidal type II cells and flattened type I cells. The type I cells occupy all surface area of the lung though their number is less than Type II cells.

 Ref : Murray