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Chapter 17: Mechanics of Breathing (Ventilation (when pressures are equal,…
Chapter 17: Mechanics of Breathing
The Respiratory System
respiratory systems always possess a large surface area compressed into a small space
air flow requires a muscular pump to create pressure gradients
primary functions of the respiratory system
exchange of gases between the atmosphere and the blood
homeostatic regulation of body pH
protection from inhaled pathogens and irritating substances
vocalization
cellular respiration: intracellular reaction of oxygen with organic molecules to produce carbon dioxide, water and energy in the form of ATP
external respiration: movement of gases between the environment and the body's cells
exchange of air between the atmosphere and the lungs (ventilation)
inspiration/inhalation: movement of air into the lungs
expiration/exhalation: movement of air out of the lungs
exchange of O2 and CO2 between the lungs and the blood
transport of O2 and CO2 by the blood
exchange of gases between blood and cells
Structures
conducting system of passages (airways) that lead from the external environment to the exchange surface of the lungs
alveoli form the exchange surface where O2 moves from inhaled air to the blood and CO2 moves from the blood to air that is about to be exhaled
bones and muscles of the thorax and abdomen
upper respiratory tract: consists of the mouth, nasal cavity, pharynx and larynx
lower respiratory tract (thoracic portion): consists of the trachea, two primary bronchi, their branches and the lungs
lungs consist of light, spongy tissue whose volume is occupied mostly by air-filled spaces
bronchi connect the lungs to the trachea
surrounded by a double-walled pleural sac whose membranes line the inside of the thorax and cover the outer surface of the lungs; layers are held together by the pleural fluid
airways and bronchi condition the air before it reaches the alveoli
warm air to body temperature
add water vapor so the epithelium does not dry out
filtering out foreign material (defense/immune mechanism)
surfactant: a chemical which mixes with the fluid lining of the alveoli to aid the lungs as they expand during breathing
pulmonary circulation is high-flow, low-pressure
Ventilation
respiratory cycle: consists of an inspiration followed by an expiration
pulmonary function tests use a spirometer, an instrument that measures the volume of air moved with each breath
tidal volume: volume of air that moves during a single inspiration or expiration
inspiratory reserve volume: additional volume you inspire above the tidal volume
expiratory reserve volume: amount of air forcefully exhaled after the end of a normal expiration
residual volume: volume of air in the respiratory system after maximal exhalation
vital capacity: sum of the inspiratory reserve volume, expiratory reserve volume and tidal volume; represents the maximum amount of air that can be voluntarily moved into or out of the respiratory system with one breath
total lung capacity: vital capacity plus the residual volume
inspiratory capacity=tidal volume+inspiratory reserve volume
functional residual capacity=expiratory reserve volume+residual volume
air flows in response to a pressure gradient and flow decreases as the resistance of the system to flow increases
when pressures are equal, there is no air flow; air flow into the alveoli increases pressure until the thoracic cage stops expanding
during expiration, lung and thoracic volumes decrease as air pressure in the lungs increases
active expiration: occurs during voluntary exhalations and when ventilation exceeds 30-40 breaths per minute
pneumothorax: the condition of a collapsed lung that is unable to function normally that results from an opening of the pleural cavity to the atmosphere
compliance: the ability of the lung to stretch
elastance: the ability to resist being deformed
restrictive lung diseases: pathological conditions in which compliance is reduced
pulmonary fibroses: development of stiff, fibrous scar tissue that restricts lung inflation
law of LaPlace: the pressure inside a bubble formed by a fluid film is a function of two factors: the surface tension of the fluid and the radius of the bubble
bronchoconstriction: increases resistance to air flow and decreases the amount of fresh air that reaches the alveoli
bronchodilation: increased CO2 in expired air relaxes bronchiolar smooth muscle
total pulmonary ventilation: the volume of air moved into and out of the lungs each minute
anatomic dead space: conducting airways that do not exchange gases with the blood
alveolar ventilation: the amount of fresh air that reaches the alveoli each minute; = ventilation rate * (tidal volume - dead space)
maximum voluntary ventilation: involves breathing as deeply and quickly as possible
obstructive lung diseases: diseases in which air flow is diminished because of increased airway reistance
asthma: inflammatory condition that is characterized by bronchoconstriction and airway edema
Gas Laws
Dalton's law: the total pressure exerted by a mixture of gases is the sum of the pressures exerted by the individual gases
partial pressure: the pressure of a single gas in a mixture
Boyle's law: if the volume of a gas is reduced, the pressure increases; if the volume increases, the pressure decreases