Transcript PULMONARY PHYSIOLGY

PULMONARY
PHYSIOLOGY
Gary L. Weinstein M.D.
Director of Pulmonary and Critical
Care Medicine
Presbyterian Hospital of Dallas
Physiology for Dummies
“Good Air In, Bad Air Out”
Physiology for Psychologists
Take Slow, Deep, “Cleansing” Breaths
Physiology for Internists
• Remember (review ?) your little orange
book from 1st year med school on
Respiratory Physiology by Dr. West
• You MUST understand normal physiology
to understand abnormal physiology
• You may BORROW my tape on normal
lung sounds (especially if you have
insomnia)
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• The respiratory system is composed of
– the conducting airways (nose, mouth, larynx,
trachea, bronchial tree)
– the lungs (terminal bronchioles, alveoli)
– the parts of the CNS concerned with control of
the system (pons, medulla, cortex, Vagus…)
– the chest wall (muscles of respiration, rib cage)
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• Functions of the respiratory system include
– O2 extraction from the external environment
– CO2 elimination from the body
– maintenance of acid-base balance (along with
other TRIVIAL organs)
– phonation
– defense from the outside world
– metabolism (e.g. ACE I
ACE II)
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• Defense: each day about 10,000 liters of air
is inspired along with dust, pollen, ash,
microorgansims, toxic gases, particulates…
• Jobs include
– air conditioning - by the time air reaches the
alveoli, it is at body temp and 100 % humidified
– olfaction - a shallow sniff bring air to the nose
but not to the lung allowing “retreat”
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• Jobs (cont’d)
– filtration
• nasal hairs trap 10 - 15 um particles
• in addition, particles > 10 um impact onto the
septum and turbinates as well as the nasopharynx
• tonsils and adenoids provide immunologic defense
against biologically active materials
• particles 2 - 5 um sediment via gravity in the smaller
airways and become trapped in the mucous that lines
the airways, then are transported up and out
• particles 0.1- 0.5 um mainly stay suspended as
aerosols and about 80 % of them are exhaled
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Control of Ventilation
Central Controller
Pons, medulla, ...
Input
Sensors
Chemoreceptors,
lung and other receptors
output
Effectors
Respiratory muscles
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• Lung and other receptors
1) pulmonary stretch receptors
– lie within the airway smooth muscle
– impulses travel in the vagus nerve
– result in a slowing of respiratory rate
2) irritant receptors
– lie between airway epithelial cells
– stimulated by noxious gases, cigarette smoke, inhaled
dusts and cold air
– impulses travel up the vagus and the reflex effects include
bronchoconstriction and hyperpnea
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3) J receptors (juxta-capillary)
– impulses pass up the Vagus and result in
rapid, shallow breathing
– may play a role in the dyspnea a/w left
heart failure and ILD
4) Nose and upper airway receptors
– respond to mechanical and chemical
stimulation with sneezing, coughing and
bronchoconstriction
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• 5) Joint and muscle receptors
– Impulses from moving limbs are believed to be
part of the stimulus to ventilation during
exercise
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• Fun Facts
– Alveolar surface area is 50-100 square meters
– There are approx. 300 million alveoli, each 1/3
mm in diameter
– The blood-gas interface is approx. 0.5 microns
– O2 and CO2 move by simple diffusion
– Anatomic dead space is approx. 1 ml/lb. body wt
– Each RBC spends about 1 sec in the capillary
network and transverses 2 - 3 alveoli
– Surfactant, made by type II pneumocytes,
dramatically lowers alveolar surface tension