Transcript Chapter_024.ppt

Chapter 24
Physiology of the Respiratory System
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Slide 1
Respiratory Physiology
(Figure 24-1)
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Respiratory physiology—complex, coordinated
processes that help maintain homeostasis
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Respiratory function includes the following:
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External respiration
• Pulmonary ventilation (breathing)
• Pulmonary gas exchange
Transport of gases by the blood
Internal respiration
• Systemic tissue gas exchange
• Cellular respiration
Regulation of respiration
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Slide 2
Pulmonary Ventilation

Respiratory cycle (ventilation; breathing)
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Inspiration—moves air into the lungs
Expiration—moves air out of the lungs
Mechanism of pulmonary ventilation
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Pulmonary ventilation mechanism must establish two gas
pressure gradients (Figures 24-2 and 24-3):
• One in which the pressure within alveoli of lungs is lower than
atmospheric pressure to produce inspiration
• One in which the pressure in alveoli of lungs is higher than
atmospheric pressure to produce expiration


Pressure gradients are established by changes in size of thoracic
cavity that are produced by contraction and relaxation of muscles
(Figures 24-4 and 24-5)
Boyle’s law—the volume of gas varies inversely with pressure at
a constant temperature
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Slide 3
Pulmonary Ventilation

Mechanism of pulmonary ventilation (cont.)
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Inspiration—contraction of diaphragm produces inspiration—
as it contracts, it makes thoracic cavity larger
(Figures 24-6 and 24-7)
• Expansion of thorax results in decreased intrapleural pressure
(Pip), leading to a decreased alveolar pressure (Palv)
• Air moves into lungs when alveolar pressure (Palv) drops below
atmospheric pressure (Patm)
• Compliance—ability of pulmonary tissues to stretch, making
inspiration possible
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Slide 4
Pulmonary Ventilation

Mechanism of pulmonary ventilation (cont.)
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Expiration—a passive process that begins when inspiratory
muscles are relaxed, decreasing size of thorax
(Figures 24-8 and 24-9)
• Increasing thoracic volume increases intrapleural pressure and thus
increases alveolar pressure above atmospheric pressure
• Air moves out of lungs when alveolar pressure exceeds
atmospheric pressure
• Pressure between parietal and visceral pleura is always less than
alveolar pressure and less than atmospheric pressure; the
difference between Pip and Palv is called transpulmonary pressure
• Elastic recoil—tendency of pulmonary tissues to return to a smaller
size after having been stretched passively during expiration
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Slide 5
Pulmonary Ventilation
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Pulmonary volumes—the amounts of air moved in and
out and remaining are important to the normal exchange
of oxygen and carbon dioxide (Figure 24-11)
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Spirometer—instrument used to measure volume of air
(Figure 24-10)
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Tidal volume (TV)—amount of air exhaled after normal
inspiration
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Expiratory reserve volume (ERV)—largest volume of additional
air that can be forcibly exhaled (between 1.0 and 1.2 liters is
normal ERV)
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Inspiratory reserve volume (IRV)—amount of air that can be
forcibly inhaled after normal inspiration (normal IRV is 3.3 liters)
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Residual volume (RV)—amount of air that cannot be forcibly
exhaled (1.2 liters)
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Slide 6
Pulmonary Ventilation
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Pulmonary capacities—the sum of two or more
pulmonary volumes
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Vital capacity—the sum of IRV + TV + ERV
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Minimal volume—amount of air remaining after RV
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A person’s vital capacity depends on many factors,
including the size of the thoracic cavity and posture
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Functional residual capacity—amount of air at the
end of a normal respiration
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Total lung capacity—the sum of all four lung
volumes—the total amount of air a lung can hold
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Slide 7
Pulmonary Ventilation
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Pulmonary capacities (cont.)
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Alveolar ventilation—volume of inspired air that
reaches the alveoli
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Anatomical dead space—air in passageways that
do not participate in gas exchange (Figure 24-6)
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Physiological dead space—anatomical dead
space plus the volume of any nonfunctioning
alveoli (as in pulmonary disease)
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Alveoli must be properly ventilated for adequate
gas exchange
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Slide 8
Pulmonary Ventilation
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Pulmonary air flow—rates of air flow into/out of the
pulmonary airways
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Total minute volume—volume moved per minute
(ml/min)
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Forced expiratory volume (FEV) or forced vital capacity
(FVC)—volume of air expired per second during forced
expiration (as a percent of VC) (Figure 24-12)
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Flow-volume loop—graph that shows flow (vertically)
and volume (horizontally), with top of loop representing
expiratory flow-volume and bottom of loop representing
inspiratory flow-volume (Figure 24-13)
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Slide 9
Pulmonary Gas Exchange
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Partial pressure of gases—pressure exerted
by a gas in a mixture of gases or a liquid
(Figure 24-14)
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Law of partial pressures (Dalton’s law)—the partial
pressure of a gas in a mixture of gases is directly
related to the concentration of that gas in the mixture
and to the total pressure of the mixture
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Arterial blood Po2 and Pco2 equal alveolar Po2 and Pco2
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Slide 10
Pulmonary Gas Exchange
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Exchange of gases in the lungs takes place
between alveolar air and blood flowing through
lung capillaries (Figures 24-15 through 24-17)
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Four factors determine the amount of oxygen that
diffuses into blood:
• The oxygen pressure gradient between alveolar air and blood
• The total functional surface area of the respiratory membrane
• The respiratory minute volume
• Alveolar ventilation
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Slide 11
Pulmonary Gas Exchange
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Exchange of gases in the lungs (cont.)
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Structural factors that facilitate oxygen diffusion
from alveolar air to blood:
• Walls of the alveoli and capillaries form only a very thin
barrier for gases to cross
• Alveolar and capillary surfaces are large
• Blood is distributed through the capillaries in a thin layer
so each red blood cell comes close to alveolar air
(Figure 24-18)
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Slide 12
How Blood Transports Gases
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Oxygen and carbon dioxide are transported as solutes and as
parts of molecules of certain chemical compounds
Transport of oxygen
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Hemoglobin is made up of four polypeptide chains (two alpha chains,
two beta chains), each with an iron-containing heme group; carbon
dioxide can bind to amino acids in the chains, and oxygen can bind to
iron in the heme groups (Figure 24-19)
 Oxygenated blood contains about 0.3 ml of dissolved O2 per 100 ml
of blood
 Hemoglobin increases the oxygen-carrying capacity of blood
(Figure 24-20)
 Oxygen travels in two forms: as dissolved O2 in plasma and associated
with hemoglobin (oxyhemoglobin)
• Increasing blood Po2 accelerates hemoglobin association with oxygen
(Figure 24-21)
• Oxyhemoglobin carries the majority of the total oxygen transported by blood
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Slide 13
How Blood Transports Gases
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Transport of carbon dioxide (CO2)
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A small amount of CO2 dissolves in plasma and is
transported as a solute (10%)
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Less than one fourth of blood CO2 combines with NH2
(amine) groups of hemoglobin and other proteins to form
carbaminohemoglobin (20%) (Figure 24-22)
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Carbon dioxide association with hemoglobin is accelerated
by an increase in blood Pco2 (Figure 24-23)
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More than two thirds of the carbon dioxide is carried
in plasma as bicarbonate ions (70%) (Figures 24-24
through 24-26)
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Slide 14
Systemic Gas Exchange
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Exchange of gases in tissues takes place
between arterial blood flowing through tissue
capillaries and cells (Figure 24-27)
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Oxygen diffuses out of arterial blood because the
oxygen pressure gradient favors its outward diffusion
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As dissolved oxygen diffuses out of arterial blood,
blood Po2 decreases, which accelerates
oxyhemoglobin dissociation to release more oxygen
to plasma for diffusion to cells (Figure 24-28)
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Slide 15
Systemic Gas Exchange
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Carbon dioxide exchange between tissues
and blood takes place in the opposite direction
from oxygen exchange
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Bohr effect—increased Pco2 decreases the affinity
between oxygen and hemoglobin (Figure 24-29, A)
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Haldane effect—increased carbon dioxide loading
caused by a decrease in Po2 (Figure 24-29, B)
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Slide 16
Regulation of Pulmonary Function
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Respiratory control centers—the main integrators
that control the nerves that affect inspiratory and
expiratory muscles are located in the brainstem
(Figure 24-30)
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Medullary rhythmicity center—generates the basic rhythm
of respiratory cycle
• This area consists of two interconnected control centers:
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Inspiratory center stimulates inspiration
Expiratory center stimulates expiration
Basic breathing rhythm can be altered by different inputs
to medullary rhythmicity center (Figure 24-30)
• Input from apneustic center in pons stimulates inspiratory center to
increase length and depth of inspiration
• Pneumotaxic center—in pons—inhibits apneustic center and
inspiratory center to prevent overinflation of lungs
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Slide 17
Regulation of Pulmonary Function
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Factors that influence breathing—sensors from the nervous system
provide feedback to medullary rhythmicity center (Figure 24-31)
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Changes in the Po2, Pco2 and pH of arterial blood influence medullary
rhythmicity area
• Pco2 acts on central chemoreceptors in medulla—if it increases, result is
faster breathing; if it decreases, result is slower breathing
• A decrease in blood pH stimulates peripheral chemoreceptors in the
carotid and aortic bodies, and even more so, the central chemoreceptors
(because they are surrounded by unbuffered fluid)
• Arterial blood Po2 presumably has little influence if it stays above a
certain level
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Arterial blood pressure controls breathing through respiratory
pressoreflex mechanism
 Hering-Breuer reflexes help control respirations by regulating depth of
respirations and volume of tidal air
 Cerebral cortex influences breathing by increasing or decreasing rate
and strength of respirations
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Slide 18
Regulation of Pulmonary Function
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Ventilation and perfusion (Figure 24-32)
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Alveolar ventilation—air flow to the alveoli
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Alveolar perfusion—blood flow to the alveoli
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Efficiency of gas exchange can be maintained by
limited ability to match perfusion to ventilation—for
example, vasoconstricting arterioles that supply
poorly ventilated alveoli and allow full blood flow to
well-ventilated alveoli
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Slide 19
The Big Picture:
Respiratory System and the Whole Body
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The internal system must continually get new oxygen and rid
itself of carbon dioxide because each cell requires oxygen and
produces carbon dioxide as a result of energy conversion
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Specific mechanisms involved in respiratory function:
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Blood gases need blood and the cardiovascular system to be
transported between gas exchange tissues of lungs and various
systemic tissues of body
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Regulation by the nervous system adjusts ventilation to compensate for
changes in oxygen or carbon dioxide levels in internal environment
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Skeletal muscles of the thorax aid airways in maintaining flow of fresh air
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Skeleton houses the lungs, and the arrangement of bones facilitates the
expansion and recoil of the thorax
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Immune system prevents pathogens from colonizing the respiratory tract
and causing infection
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Slide 20