RESPIRATORY DISORDERS - Medicine for Mountaineering and Other Wilderness Activities - page 232

CHAPTER 18
RESPIRATORY DISORDERS
Colin K. Grissom, M.D.
Principal Contributor
The respiratory system moves air inandoutofthe lungstoprovide oxygenforthe bodyand
to eliminate carbon dioxide ( Fig. 9-1 ). The components of this system are:
The upper respiratory tract includes the nose, mouth, and larynx (vocal cords and voice
box). On inspiration, air moves through the upper respiratory tract and is filtered to re-
move foreign particles, saturated with water, and warmed to body temperature.
The lower respiratory tract starts with the trachea just below the larynx and includes the
divisions of the airways down to the alveoli, or microscopic air sacs, that make up the
major portion of the lung tissue, and in which oxygen and carbon dioxide are exchanged
between blood and air. The trachea descends into the chest and divides into the right and
left bronchi that supply each lung. The bronchi then repeatedly subdivide in each lung
until,aftersometwenty-threedivisions,thealveoliarereached.Inthealveolionlyavery
thin membrane separates air in the sacs and blood in pulmonary capillaries.
The bellows: During inspiration the diaphragm contracts and lowers, causing the chest
walltoexpand,whichmovesairintothelungs.Duringexercise,musclesoftheneckand
muscles between the ribs may also assist with expanding the chest. Expiration, or move-
ment of air out of the lungs, occurs passively at rest as the diaphragm and chest wall
relax. During heavy exercise, contraction of the abdominal muscles may assist with ex-
piration byforcing air outofthelungs.Athinmembrane—the pleura—covers thelungs,
lines the inner surface of the chest wall, and eases the movement of the lungs within the
chest.
The control system: Sensing cells that detect chemical changes in the circulating blood
(chemoreceptors), detect movements of the chest wall, diaphragm, and lungs (neurore-
ceptors); and the network of nerves that carries information from these receptors to the
brain, which controls the rate and depth of respiration.
Respiratory movements are controlled by a complex system of receptors, transmitters,
andeffectors throughout the body.Chemical receptors respond tolower oxygen,anincrease
or decrease of carbon dioxide, and a change in the acidity of the blood. These receptors sig-
nalthebraintoincreaseordecreasetherateanddepthofbreathing(ventilation).Thecarotid
bodies are a set of special receptor cells in the neck. Other receptor cells are situated deep
within the respiratory center of the brain and respond to changes in the blood circulating
through the brain and in the spinal fluid that bathes the brain.
Under ordinary resting conditions, approximately 0.5 liter of air is inspired with each
breath. The normal respiratory rate is ten to twelve breaths per minute, and the correspond-