A Jedi's Strength Flows from the Force.

GE 345: Week 3

Respiratory Tract

Updated by Tracey 23 July 02

The respiratory passageways must be kept open to allow free air movement. To accomplish this, cartilage rings extend most of the way around the trachea. Cartilage plates are present to a lesser extent in the walls of the bronchi, which maintain rigidity while allowing sufficient motion for the lungs to expand and contract. These plates are completely gone in the bronchioles.

Smooth muscle comprises the remainder of the trachea and bronchi walls. Many obstructive diseases result from narrowing of the smaller bronchi and bronchioles, often from excessive contraction of the smooth muscle.

Local bronchiole control includes:

Sympathetic Nerve Fibers: Few fibers exist in the central portions of the lung, and therefore have minimal control over bronchioles.
Hormonal: norepinephrine and epinephrine released into the blood by the adrenal gland medullae cause bronchial dilation.
Parasympathetic Control: A few parasympathetic nerves from the vagus nerves penetrate the lungs and release acetylcholine, which causes mild bronchial constriction.
Local Factors: histamine and slow-reacting anaphylaxis, which are formed in the lungs, are released during allergic reactions, causing bronchiolar constriction. These substances play key roles in airway obstruction occuring in asthma.

The nose conditions the air entering the respiratory tract by: warming it; humidifiying it; and filtering it.

Mucus secreted in the lining of the passageways coats them and keeps them moist, as well as trapping small particles, keeping them from reaching the alveoli. Cilia on the surface of the passages keeps the mucus flowing toward the pharynx, where the mucus is trapped and either swallowed or coughed to the exterior.