Physiology 31 Lecture
Chapter 17 – Mechanics of Breathing
I. Overview
A. Respiratory System Introduction
B. Gas Laws
C. Mechanics of Ventilation
D. Neural Control of Ventilation
E. Gas Exchange & Transport
F. Blood Chemistry
G. Respiratory Disorders
II. Introduction to the Respiratory System
A. The major role of this system is to supply body tissues with ___________ and dispose of
carbon __________ (gas exchange)
B. _______________ refers to 4 main functions:
1. Pulmonary ____________ - breathing
2. External respiration - gas exchanges between the air & blood at the lung
___________
3. Transportation of respiratory gases via the ________ system
4. Internal respiration – gas exchange between ___________ and surrounding tissues
C. The respiratory system aids in regulating blood ____ by CO2 retention and excretion
D. Respiratory __________ protects the body from inhaled pathogens
E. Air moving across the ________ cords produces vocalizations
F. The respiratory system can be divided ____________ into upper & lower divisions, and
__________ into a conducting & a respiratory division
G. Basic _____________ of the Respiratory System
1. Major _________ & structures of the respiratory system are the
a. ________ respiratory - nasal cavity, pharynx, larynx, and trachea superior to the
lungs
b. ________ respiratory - bronchi, bronchioles, and pulmonary alveoli within the
lungs
2. Air passes from nasal cavity  pharynx  larynx  ______  bronchi 
bronchioles  _________
3. The __________ division includes all the cavities and structures that transport gases to
& from the pulmonary alveoli; also called anatomical ______ space because no gas
exchange takes place there
4. The ___________ division consists of the pulmonary ________, which are the
functional units of the respiratory system, where _____ exchange between the air and
blood occur
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III. Pulmonary Alveoli, Lungs, & Pluera
A. Pulmonary Alveoli
1. Alveolar sacs are clusters of tiny pulmonary __________, the functional units of the
respiratory system. Alveolar ______ are
a. Type I – simple _________ epithelium surrounded by a basal lamina, forming a
thin respiratory membrane shared by alveoli and surrounding capillaries
b. Type II – _________ epithelium that secretes lubricating __________ that keeps
alveoli from sticking together
c. Alveolar ______________ that phagocytize pathogens
2. Gas exchange occurs across the respiratory _________ between the alveoli and their
associated capillaries
a. ________ diffuses across the alveoli walls into the capillaries
b. ________ diffuses from the capillaries into the alveoli
B. Lungs - paired respiratory organs lateral to the mediastinum, surrounded by the ribs and
_________ muscles, with the muscular ____________ at their base
C. __________ - serous membranes that surround the lungs and line the thoracic cavity
include the
1. _________ pleura adheres to the outer lung surface and extends into the interlobular
fissures
2. ________ pleura lines the thoracic cavity and the mediastinum, thus both lungs are in
separate compartments
3. A pleural ________ is a potential space between the visceral & parietal pleura;
pleural ___ in this cavity allows the membranes to slide smoothly across each other
during respiration
4. _______ is an inflammation of the pleura, which causes friction between lungs and
thoracic cavity, making breathing difficult
IV. Mechanics of Ventilation
A. Pulmonary ventilation (breathing) consists of two phases: __________ (inhaling) and
___________ (exhaling)
B. Relaxed inspiration involves contractions of the diaphragm and external intercostal
muscles
1. Contraction of the dome-shaped __________ causes it to flatten, increasing lung
volume; contractions of the external intercostals lift the ribs, further increasing lung
volume
a. ________ Law – the pressure of a quantity of gas is inversely proportional to the
volume of its container (___1/___)
b. During inspiration alveolar volume increases, which ___________
intrapulmonary pressure below atmospheric pressure (760 mm Hg  757 mm
Hg)
c. Because atmospheric pressure is now higher than intrapulmonary pressure, air
flows ______ the lungs
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d. ______________ pressure (≈754 mm Hg) is the pressure in the pleural cavity,
which is always more negative than the intrapulmonary pressure, and acts as a
__________ to keep lungs inflated
e. ________________ pressure is the difference between the intrapulmonary and
intrapleural pressures (757  754 mm Hg); this helps the lungs to expand in the
thoracic cavity
C. __________ inspiration involves contractions of the scalenes and sternocleidomastoid
muscles, which further elevate the ribs
D. Relaxed ___________ - muscles of inspiration relax, ribs return to their original
position, elastic tissue in the lungs and bronchial tree allow them to recoil
1. Lung internal volume decreases, causing intrapulmonary pressure to ____________
2. Intrapulmonary pressure becomes +3 mm Hg above atmospheric pressure, so air flows
_____ of the lungs
E. During _________ expiration, internal intercostals and abdominal muscles contract in
response to intercostal and lower spinal nerves
F. Other ________ affecting respiration include resistance to airflow, alvoelar surface
tension, and alveolar ventilation
1. __________ to airflow within airways is affected by pulmonary compliance and
bronchiole diameter (F  Pressure/Resistance)
a. Pulmonary _______________, the ease with which the lungs expand, can be
reduced by lung diseases that increase resistance, thus decreasing air flow
b. Changes in bronchiole ____________ affect resistance
1) Broncho___________ occurs when parasympathetic nerves or ___________
constrict bronchioles, leading to increased resistance and decreased air flow
2) Broncho_______ occurs when __________, released by the adrenal gland
during exercise or stress, dilates bronchioles, leading to decreased resistance and
increased air flow
2. Alveolar ________ __________ is reduced by surfactant
a. ____________ is a lipoprotein produced by type ___ alveolar cells; it reduces
alveolar surface tension, allowing the alveoli to recoil during expiration
b. Premature infants are often deficient in surfactant, which causes hyaline
membrane disease (Respiratory ________ Syndrome)
3. Alveolar ventilation is limited by the amount of air that reaches functional
___________
a. The conducting division of the respiratory system is called ___________ dead
space because air here is not involved in _____ exchange
b. ____________ dead space is the sum of the anatomical dead space and
pathological alveolar dead space
c. Alveolar ____________ _______ is determined by taking the difference of the
inhaled air (500 ml) minus the dead air (150 ml), then multiplying the result by
the respiratory rate (BPM)
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G. Measurements of Ventilation can be obtained via a __________, which captures expired
air and records the rate and depth of breathing, speed of expiration, and rate of oxygen
consumption. Measurements are respiratory __________ or respiratory capacities
1. _________ volume (TV) - amount of air inhaled or exhaled in one respiratory cycle
(500 mL)
2. _____________ reserve volume (IRV) – amount of air above the tidal volume that
can be inhaled with maximum effort (3,000 mL)
3. ______________ reserve volume (ERV) – amount of air above the tidal volume
that can be exhaled with maximum effort (1,200 mL)
4. ___________ volume (RV) – amount of air left in lungs after maximum expiration
(1,300 mL)
5. Vital ___________ – amount of air that can be exhaled with maximum effort after
maximum inspiration (VC = TV + IRV + ERV) (4,700 mL)
6. __________ expiratory volume (FEV) – percent of the vital capacity that can be
exhaled in a given time interval.
a. Healthy adults should be able to expel 75-85% of the vital capacity in one
second.
b. Inability to do so may indicate respiratory problems
7. Total lung capacity (____) = inspiratory capacity (TV+IRV) + residual volume
V. Neural Control of Ventilation
A. The three respiratory centers of the _______ are the
1. Rhythmicity area in the __________ oblongata contains nerve cell bodies that form
the inspiratory and expiratory portions
a. Inspiratory (I) neurons fire during __________
b. Expiratory (E) neurons fire during forced __________
2. Apneustic & pneumotaxic areas in the ______ influence the activity of the
rhythmicity area
a. ___________ center prolongs inspiration
b. ____________ center inhibits medullary inspiratory neurons
B. Excessive inflation in the lungs triggers the ______-______ reflex, in which inspiratory
neurons are inhibited and expiration results
C. Breathing can be voluntarily controlled to a point. Holding one’s breath lowers the ___
level and raises the ____ level in the blood until autonomic controls force the person to
breath
VI. Gas Exchange & Transport
A. Air is a mixture of _________: 78.6% N2, 20.9% O2, 0.46% H2O, and 0.04% CO2 (note
that alveolar air differs in percentages)
1. Each gas contributes a partial ________ to the total atmospheric pressure in proportion
to its percentage (e.g., Patm = PN2 + PO2 + PH2O + PCO2 = 597 + 159 + 3.7 + 0.3 =
760 mm Hg)
2. _______ Law – the total pressure of a gas mixture is the _____ of the partial pressures
of the individual gases
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3. Partial gas pressures are important because they determine the rate of ___________ of
a gas, and thus affect the rate of gas exchange between the blood and alveolar air
B. At the Air-Water Interface (as in the pulmonary ___________), gases diffuse down
their concentration gradients until __________ is reached
1. _________ Law – the amount of gas that dissolves in a liquid is proportional to
a. the partial __________ of the gas and
b. the _____________ of the gas
C. Gas ___________ – the process of carrying gases from the alveoli to the systemic tissues
and back
1. _______ transport is accomplished mainly by O2 binding to ___ (98.5%), with a slight
percentage dissolved in the plasma (1.5%)
a. At ____ PO2 (as in the lungs), Hb has a high ________ for O2; the iron in each of
the 4 heme groups binds one O2 molecule, and Hb becomes _____hemoglobin
b. At ____ PO2 (as in the tissues), Hb has a low affinity for O2, so the heme groups
______ the O2 to diffuse out to the tissues. Once the O2 is released, the Hb
becomes _______hemoglobin
c. Hb has a higher affinity for ____ than it does for O2, so if CO is present, it will
_____________ bind to Hb, preventing O2 from binding, which can lead to death
2. Carbon _________ transport is accomplished in three ways: as carbonic acid,
carbamino compounds, and dissolved gas
a. About ___% of CO2 reacts with water to form _________ acid (H2CO3), which then
dissociates into __________ (HCO3-) and hydrogen ions (H+) in RBCs. This rxn.
is facilitated by the enzyme carbonic __________ (CAH)
CO2 + H2O  H2CO3  HCO3- + H+
CAH
b. About ___% of CO2 binds with hemoglobin to form ___________hemoglobin
(HbCO2). CO2 does not compete with O2 because they bind to different ______ on
Hb.
c. The remaining ___% of CO2 is carried in blood __________ as a dissolved gas, like
the CO2 in soda pop (note: CAH is present in RBCs, but not in plasma)
D. __________ Gas Exchange is the unloading of O2 and loading of CO2 at the systemic
capillaries in _________
1. ____ loading – CO2 is a by product of cellular ___________ in tissues, therefore
PCO2 is higher in tissues than in capillaries, thus CO2 diffuses _____ the bloodstream
2. _________ unloading- _______ ions dissociated from carbonic acid bind to
___hemoglobin, which reduces Hb’s affinity for O2, causing the release of ___, which
diffuses to surrounding tissues
E. ________ gas exchange is the loading of ____ and unloading of CO2 at the alveolar
capillaries
1. More PO2 in alveolar air than in capillary blood allows O2 to diffuse into the _______
(O2 loading)
a. As Hb loads O2, its affinity for ___ declines
b. Hydrogen ions dissociate from Hb and bind with ________ ions transported from
the plasma into RBCs
c. The reaction of H+ and HCO3- reverses the previous hydration rxn. and generates
free _____
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2. Greater PCO2 in the capillary blood than in the alveolus allows ____ to diffuse into the
__________ (CO2 unloading)
3. Even though P O2 is  PCO2, _______ amounts of O2 and CO2 are exchanged across
the respiratory membrane because CO2 is much more _________ than O2
F. Adjustment to Changing Metabolic Needs of Tissues
1. Four factors adjust the rate of ____ unloading
a. Ambient O2 - _______ tissues consume O2 rapidly, leading to a lower P O2 than
resting tissues, thus Hb O2 releases more O2 to active tissues
b. ___________ – elevated temperature in active tissues also promotes O2 unloading
c. ______ effect – active tissues generate extra _____, which raises the ___
concentration and lowers blood pH; this also promotes O2 unloading
d. Bisphosphoglycerate (____), an enzyme in anerobic respiration in RBCs, binds to
Hb and promotes ___ unloading
2. CO2 loading is affected by a low level of ______, which enables Hb to transport more
_____ (the Haldane effect)
VII. Blood Chemistry & Respiratory Rhythm
A. Two groups of _______receptors respond to changes in blood chemistry
1. _________ chemoreceptors in the MO monitor the ___ of the CSF and tissue fluid
of the brain
2. ____________ chemoreceptors in the aortic and carotid bodies
a. ________ bodies in the aortic arch send sensory information to the MO in the
_______ nerves
b. ________ bodies in the carotid arteries stimulate sensory fibers in the
_________pharyngeal nerve
B. Effects of hydrogen ions, O2 and CO2 concentrations on respiration
1. Hydrogen ion concentration (___) in the brain is controlled mainly by ventilation
a. Blood pH is determined largely by P____ because of the rxn. CO2 + H2O 
H2CO3  HCO3- + H+
b. The more CO2 is present, the more ___ is generated, the lower the ____; less CO2 =
less H+ ions = higher pH
c. Blood pH must be maintained within a narrow range of 7.35-7.45; lower is called
________, higher is ____________
d. Respiratory __________ is usually caused by excess _____ (hypercapnia), which
can be corrected by ____________ ventilation to expel more CO2
e. Respiratory ___________ is usually caused by low _____ (hypocapnia), which can
be corrected by _____________ ventilation to allow CO2 to build up in the blood
2. Carbon dioxide – at the beginning of exercise, rising ____ levels stimulate peripheral
______receptors, which trigger an __________ in ventilation
3. ____________ – PO2 usually has little effect on ventilation, but long term hypoxemia
(as in emphysema and mountain climbing) can trigger __________ drive, in which
ventilation is increased
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X. Respiratory Disorders
A. __________, a deficiency of O2 in the tissues, can cause cyanosis and, if severe and
prolonged, can lead to tissue necrosis
B. Trauma or Injury Problems
1. _______________ is a condition in which the lung(s) collapse (atelectasis) if air enters
the pleural cavity.
2. Choking - foreign object lodges in the trachea; may be dislodged by the
______________ maneuver
C. Chronic obstructive pulmonary diseases (_______s)
1. ______________ - acute infection & inflammation of the lung accompanied by fluid
buildup; may be caused by bacteria, virus, or fungus
2. _____________ - inflammatory lung disease contracted by inhaling tuberculosis
bacteria from a carrier
3. ____________ - caused by allergy to inhaled antigens; causes a swelling or blockage
of lower respiratory tubes
4. Chronic ____________ – often found in smokers, tobacco smoke paralyzes and
eventually destroys _______ and alveolar macrophages; excess _________
production leads to coughing and infection
5. ___________ - causes the breakdown of the pulmonary ______, increasing the size of
air spaces and decreasing their surface area and respiration; frequent cause of death
among _________.
D. Lung ________, which causes 1/3 of all cancer deaths in the U.S., is caused mostly by
__________ smoke, which contains numerous carcinogenic compounds
1. Three forms of lung cancer are ___________ cell carcinoma, adenocarcinoma, and
small-cell carcinoma
2. Symptoms include chronic coughing and ______ in the sputum
3. Lung cancer _____________ so rapidly, it has usually spread to other organs by the
time it is diagnosed, and prognosis is poor