Respiratory Deposition

:: Section 2

Respiratory System

Characteristics of the various regions in the respiratory system are shown in the table below. As you can see from the table, as it goes deeper in the system, the diameter and the length decrease while the number of branchings increases. This increase results in a decreasing velocity and increasing residence time that have great impact on the "effective mechanisms" responsible for deposition.

Airway	Gener- ation of Branchings	Number of Branchings	Diameter of Airway (mm)	Length of Airway (mm)	Total Cross- Section Area (cm²)	Velocity (mm/s)	Residence Time in the Airway (ms)
Trachea	0	1	18	120	2.5	3900	30
Main bronchus	1	2	12	48	2.3	4300	11
Segmental bronchus	4	16	4.5	13	2.5	3900	3.2
Terminal bronchus	11	2000	1.1	3.9	20	520	7.4
Terminal bronchiole	16	66000	0.6	1.6	180	54	31
Alveolar duct	21	2 x 10⁶	0.43	0.7	3200	3.2	210
Alveolar sac	23	8 x 10⁶	0.41	0.5	72000	0.9	550
Alveoli		3 x 10⁸	0.28	0.2

Why does the residence time affect particle deposition?

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