Trachea cross section

The simplified flow analysis of Weibefs model A indicates undeveloped flow with a flat profile in the trachea for Reynolds numbers up to approximately 2,000. However, this does not consider disturbances produced by the rough walls, the eccentricity of the cross section, and the larynx. 

The form in which elastin is laid down varies considerably in the different types of elastic tissue. Membranes with a very high elastin content are found in the walls of the larger arteries, in some parts of the heart, and in the trachea and bronchi. In the larger arteries the structural units of the elastic tissue formation are concentric lamellae which are often of rather variable thickness and always contain many irregular openings. In the ligamentum nuchae of some animals, particularly the ox, the structure is quite different and thick longitudinal elastic fibers, of almost circular cross section, form most of the tissue. 

Fig. so.—Vascular elements. A, annular tracheal tube B, spiral trachea tube C, reticulated tracheal tube D, pitted tracheal tube E, cross-section through plate of seive tube, and adjoining companion cell F, length-wise section of sieve tube G, portions of two companion cells. (A, B, C, D, Robbins E, F, and G, after Strasburger.)... 

Fig. 2. The central respiratory passages trachea and bronchi. (The inset is a cross section describing the cellular organization within the trachea.)...

Here, we have applied Murray s law for the bronchial tree, r, = ro n (Weibel, 1984), connecting radii of downstream branches, r,-, to that of the trachea, tQ. Note that m = 1 for mammalian lungs. The tree s total cross-sectional area therefore increases exponentially with branching generation according to Eqn. 3, resulting in a drastic decrease of the oxygen velocity within the deeper airway branches as compared to the trachea. 

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