chapter 24 physiology of the respiratory system

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Chapter 24Chapter 24 Physiology of the Respiratory System Physiology of the Respiratory System


Respiratory Physiology Respiratory Physiology

Respiratory physiology—complex, coordinated Respiratory physiology—complex, coordinated processes that help maintain homeostasisprocesses that help maintain homeostasis

Respiratory function includes the following:Respiratory function includes the following: External respiration External respiration

• Pulmonary ventilation (breathing)Pulmonary ventilation (breathing)

• Pulmonary gas exchangePulmonary gas exchange

Transport of gases by the bloodTransport of gases by the blood Internal respirationInternal respiration

• Systemic tissue gas exchange Systemic tissue gas exchange

• Cellular respirationCellular respiration

Regulation of respirationRegulation of respiration


Pulmonary VentilationPulmonary Ventilation Respiratory cycle (ventilation; breathing)Respiratory cycle (ventilation; breathing)

Inspiration—moves air into the lungsInspiration—moves air into the lungs Expiration—moves air out of the lungsExpiration—moves air out of the lungs

Mechanism of pulmonary ventilationMechanism of pulmonary ventilation Pulmonary ventilation mechanism must establish two gas Pulmonary ventilation mechanism must establish two gas

pressure gradients :pressure gradients :• One in which the pressure within alveoli of lungs is lower than One in which the pressure within alveoli of lungs is lower than

atmospheric pressure to produce inspirationatmospheric pressure to produce inspiration

• One in which the pressure in alveoli of lungs is higher than One in which the pressure in alveoli of lungs is higher than atmospheric pressure to produce expirationatmospheric pressure to produce expiration

Pressure gradients are established by changes in size of Pressure gradients are established by changes in size of thoracic cavity that are produced by contraction and relaxation of thoracic cavity that are produced by contraction and relaxation of muscles muscles

Boyle’s law—the volume of gas varies inversely with pressure at Boyle’s law—the volume of gas varies inversely with pressure at a constant temperaturea constant temperature


Pulmonary VentilationPulmonary Ventilation

Mechanism of pulmonary ventilation (cont.)Mechanism of pulmonary ventilation (cont.)

Inspiration—contraction of diaphragm produces inspiration—Inspiration—contraction of diaphragm produces inspiration—as it contracts, it makes thoracic cavity larger as it contracts, it makes thoracic cavity larger

• Expansion of thorax results in decreased intrapleural pressure Expansion of thorax results in decreased intrapleural pressure (Pip), leading to a decreased alveolar pressure (Palv)(Pip), leading to a decreased alveolar pressure (Palv)

• Air moves into lungs when alveolar pressure (Palv) drops below Air moves into lungs when alveolar pressure (Palv) drops below atmospheric pressure (Patm)atmospheric pressure (Patm)

• Compliance—ability of pulmonary tissues to stretch, making Compliance—ability of pulmonary tissues to stretch, making inspiration possibleinspiration possible



Mechanism of pulmonary ventilation (cont.)Mechanism of pulmonary ventilation (cont.)

Expiration—a passive process that begins when inspiratory Expiration—a passive process that begins when inspiratory muscles are relaxed, decreasing size of thorax muscles are relaxed, decreasing size of thorax

• Increasing thoracic volume increases intrapleural pressure and thus Increasing thoracic volume increases intrapleural pressure and thus increases alveolar pressure above atmospheric pressureincreases alveolar pressure above atmospheric pressure

• Air moves out of lungs when alveolar pressure exceeds atmospheric Air moves out of lungs when alveolar pressure exceeds atmospheric pressurepressure

• Pressure between parietal and visceral pleura is always less than Pressure between parietal and visceral pleura is always less than alveolar pressure and less than atmospheric pressure; the alveolar pressure and less than atmospheric pressure; the difference between Pip and Palv is called transpulmonary pressuredifference between Pip and Palv is called transpulmonary pressure

• Elastic recoil—tendency of pulmonary tissues to return to a smaller Elastic recoil—tendency of pulmonary tissues to return to a smaller size after having been stretched passively during expirationsize after having been stretched passively during expiration



Pulmonary volumes—the amounts of air moved in and Pulmonary volumes—the amounts of air moved in and out and remaining are important to the normal exchange out and remaining are important to the normal exchange of oxygen and carbon dioxide of oxygen and carbon dioxide Spirometer—instrument used to measure volume of air Spirometer—instrument used to measure volume of air Tidal volume (TV)—amount of air exhaled after normal Tidal volume (TV)—amount of air exhaled after normal

inspirationinspiration Expiratory reserve volume (ERV)—largest volume of additional Expiratory reserve volume (ERV)—largest volume of additional

air that can be forcibly exhaled (between 1.0 and 1.2 liters is air that can be forcibly exhaled (between 1.0 and 1.2 liters is normal ERV)normal ERV)

Inspiratory reserve volume (IRV)—amount of air that can be Inspiratory reserve volume (IRV)—amount of air that can be forcibly inhaled after normal inspiration (normal IRV is 3.3 liters)forcibly inhaled after normal inspiration (normal IRV is 3.3 liters)

Residual volume (RV)—amount of air that cannot be forcibly Residual volume (RV)—amount of air that cannot be forcibly exhaled (1.2 liters)exhaled (1.2 liters)



Pulmonary capacities—the sum of two or more Pulmonary capacities—the sum of two or more pulmonary volumespulmonary volumes

Vital capacity—the sum of IRV + TV + ERVVital capacity—the sum of IRV + TV + ERV

Minimal volume—amount of air remaining after RVMinimal volume—amount of air remaining after RV

A person’s vital capacity depends on many factors, A person’s vital capacity depends on many factors, including the size of the thoracic cavity and postureincluding the size of the thoracic cavity and posture

Functional residual capacity—amount of air at the end of Functional residual capacity—amount of air at the end of a normal respirationa normal respiration

Total lung capacity—the sum of all four lung volumes—Total lung capacity—the sum of all four lung volumes—the total amount of air a lung can holdthe total amount of air a lung can hold



Pulmonary capacities (cont.)Pulmonary capacities (cont.)

Alveolar ventilation—volume of inspired air that Alveolar ventilation—volume of inspired air that reaches the alveolireaches the alveoli

Anatomical dead space—air in passageways that Anatomical dead space—air in passageways that do not participate in gas exchange do not participate in gas exchange

Physiological dead space—anatomical dead Physiological dead space—anatomical dead space plus the volume of any nonfunctioning space plus the volume of any nonfunctioning alveoli (as in pulmonary disease)alveoli (as in pulmonary disease)

Alveoli must be properly ventilated for adequate Alveoli must be properly ventilated for adequate gas exchangegas exchange



Pulmonary air flow—rates of air flow into/out of the Pulmonary air flow—rates of air flow into/out of the pulmonary airwayspulmonary airways

Total minute volume—volume moved per minute Total minute volume—volume moved per minute (ml/min)(ml/min)

Forced expiratory volume (FEV) or forced vital capacity Forced expiratory volume (FEV) or forced vital capacity (FVC)—volume of air expired per second during forced (FVC)—volume of air expired per second during forced expiration (as a percent of VC) (Figure 24-12)expiration (as a percent of VC) (Figure 24-12)

Flow-volume loop—graph that shows flow (vertically) Flow-volume loop—graph that shows flow (vertically) and volume (horizontally), with top of loop representing and volume (horizontally), with top of loop representing expiratory flow-volume and bottom of loop representing expiratory flow-volume and bottom of loop representing inspiratory flow-volume inspiratory flow-volume


Pulmonary Gas ExchangePulmonary Gas Exchange

Partial pressure of gases—pressure exerted Partial pressure of gases—pressure exerted by a gas in a mixture of gases or a liquid by a gas in a mixture of gases or a liquid

Law of partial pressures (Dalton’s law)—the partial Law of partial pressures (Dalton’s law)—the partial pressure of a gas in a mixture of gases is directly pressure of a gas in a mixture of gases is directly related to the concentration of that gas in the mixture related to the concentration of that gas in the mixture and to the total pressure of the mixtureand to the total pressure of the mixture

Arterial blood PoArterial blood Po22 and Pco and Pco22 equal alveolar Po equal alveolar Po22 and Pco and Pco22



Exchange of gases in the lungs takes place Exchange of gases in the lungs takes place between alveolar air and blood flowing through between alveolar air and blood flowing through lung capillaries lung capillaries

Four factors determine the amount of oxygen that Four factors determine the amount of oxygen that diffuses into blood:diffuses into blood:

• The oxygen pressure gradient between alveolar air and bloodThe oxygen pressure gradient between alveolar air and blood

• The total functional surface area of the respiratory membraneThe total functional surface area of the respiratory membrane

• The respiratory minute volumeThe respiratory minute volume

• Alveolar ventilationAlveolar ventilation



Exchange of gases in the lungs (cont.) Exchange of gases in the lungs (cont.)

Structural factors that facilitate oxygen diffusion Structural factors that facilitate oxygen diffusion from alveolar air to blood:from alveolar air to blood:

• Walls of the alveoli and capillaries form only a very thin Walls of the alveoli and capillaries form only a very thin barrier for gases to crossbarrier for gases to cross

• Alveolar and capillary surfaces are largeAlveolar and capillary surfaces are large

• Blood is distributed through the capillaries in a thin layer Blood is distributed through the capillaries in a thin layer so each red blood cell comes close to alveolar air so each red blood cell comes close to alveolar air

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How Blood Transports GasesHow Blood Transports Gases

Oxygen and carbon dioxide are transported as solutes and as Oxygen and carbon dioxide are transported as solutes and as parts of molecules of certain chemical compoundsparts of molecules of certain chemical compounds

Transport of oxygenTransport of oxygen Hemoglobin is made up of four polypeptide chains (two alpha chains, Hemoglobin is made up of four polypeptide chains (two alpha chains,

two beta chains), each with an iron-containing heme group; carbon 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 dioxide can bind to amino acids in the chains, and oxygen can bind to iron in the heme groupsiron in the heme groups

Oxygenated blood contains about 0.3 ml of dissolved OOxygenated blood contains about 0.3 ml of dissolved O22 per 100 ml per 100 ml of bloodof blood

Hemoglobin increases the oxygen-carrying capacity of blood Hemoglobin increases the oxygen-carrying capacity of blood Oxygen travels in two forms: as dissolved OOxygen travels in two forms: as dissolved O22 in plasma and associated in plasma and associated

with hemoglobin (oxyhemoglobin)with hemoglobin (oxyhemoglobin)

• Increasing blood PoIncreasing blood Po22 accelerates hemoglobin association with oxygen accelerates hemoglobin association with oxygen

• Oxyhemoglobin carries the majority of the total oxygen transported by bloodOxyhemoglobin carries the majority of the total oxygen transported by blood


How Blood Transports GasesHow Blood Transports Gases

Transport of carbon dioxide (COTransport of carbon dioxide (CO22)) A small amount of COA small amount of CO22 dissolves in plasma and is dissolves in plasma and is

transported as a solute (10%)transported as a solute (10%)

Less than one fourth of blood COLess than one fourth of blood CO22 combines with NH combines with NH22 (amine) groups of hemoglobin and other proteins to form (amine) groups of hemoglobin and other proteins to form carbaminohemoglobin (20%) carbaminohemoglobin (20%)

Carbon dioxide association with hemoglobin is accelerated Carbon dioxide association with hemoglobin is accelerated by an increase in blood Pcoby an increase in blood Pco22

More than two thirds of the carbon dioxide is carried More than two thirds of the carbon dioxide is carried in plasma as bicarbonate ions (70%) in plasma as bicarbonate ions (70%)


Systemic Gas ExchangeSystemic Gas Exchange

Exchange of gases in tissues takes place Exchange of gases in tissues takes place between arterial blood flowing through tissue between arterial blood flowing through tissue capillaries and cells (Figure 24-27)capillaries and cells (Figure 24-27)

Oxygen diffuses out of arterial blood because the Oxygen diffuses out of arterial blood because the oxygen pressure gradient favors its outward diffusionoxygen pressure gradient favors its outward diffusion

As dissolved oxygen diffuses out of arterial blood, As dissolved oxygen diffuses out of arterial blood, blood Poblood Po2 2 decreases, which accelerates decreases, which accelerates

oxyhemoglobin dissociation to release more oxygen oxyhemoglobin dissociation to release more oxygen to plasma for diffusion to cells (Figure 24-28)to plasma for diffusion to cells (Figure 24-28)


Systemic Gas ExchangeSystemic Gas Exchange

Carbon dioxide exchange between tissues Carbon dioxide exchange between tissues and blood takes place in the opposite direction and blood takes place in the opposite direction from oxygen exchangefrom oxygen exchange

Bohr effect—increased PcoBohr effect—increased Pco22 decreases the affinity decreases the affinity

between oxygen and hemoglobin (Figure 24-29, A)between oxygen and hemoglobin (Figure 24-29, A)

Haldane effect—increased carbon dioxide loading Haldane effect—increased carbon dioxide loading caused by a decrease in Pocaused by a decrease in Po22 (Figure 24-29, B) (Figure 24-29, B)


Regulation of Pulmonary Function Regulation of Pulmonary Function Respiratory control centers—the main integrators Respiratory control centers—the main integrators

that control the nerves that affect inspiratory and that control the nerves that affect inspiratory and expiratory muscles are located in the brainstem expiratory muscles are located in the brainstem (Figure 24-30)(Figure 24-30) Medullary rhythmicity center—generates the basic rhythm Medullary rhythmicity center—generates the basic rhythm

of respiratory cycleof respiratory cycle• This area consists of two interconnected control centers:This area consists of two interconnected control centers:

Inspiratory center stimulates inspirationInspiratory center stimulates inspiration Expiratory center stimulates expirationExpiratory center stimulates expiration

Basic breathing rhythm can be altered by different inputs Basic breathing rhythm can be altered by different inputs to medullary rhythmicity center (Figure 24-30)to medullary rhythmicity center (Figure 24-30)

• Input from apneustic center in pons stimulates inspiratory center to Input from apneustic center in pons stimulates inspiratory center to increase length and depth of inspirationincrease length and depth of inspiration

• Pneumotaxic center—in pons—inhibits apneustic center and Pneumotaxic center—in pons—inhibits apneustic center and inspiratory center to prevent overinflation of lungsinspiratory center to prevent overinflation of lungs


Regulation of Pulmonary FunctionRegulation of Pulmonary Function Factors that influence breathing—sensors from the nervous system Factors that influence breathing—sensors from the nervous system

provide feedback to medullary rhythmicity center (Figure 24-31)provide feedback to medullary rhythmicity center (Figure 24-31) Changes in the PoChanges in the Po22, Pco, Pco22 and pH of arterial blood influence medullary and pH of arterial blood influence medullary

rhythmicity arearhythmicity area

• PcoPco22 acts on central chemoreceptors in medulla—if it increases, result is acts on central chemoreceptors in medulla—if it increases, result is faster breathing; if it decreases, result is slower breathingfaster breathing; if it decreases, result is slower breathing

• A decrease in blood pH stimulates peripheral chemoreceptors in the A decrease in blood pH stimulates peripheral chemoreceptors in the carotid and aortic bodies, and even more so, the central chemoreceptors carotid and aortic bodies, and even more so, the central chemoreceptors (because they are surrounded by unbuffered fluid)(because they are surrounded by unbuffered fluid)

• Arterial blood PoArterial blood Po22 presumably has little influence if it stays above a presumably has little influence if it stays above a certain levelcertain level

Arterial blood pressure controls breathing through respiratory Arterial blood pressure controls breathing through respiratory pressoreflex mechanismpressoreflex mechanism

Hering-Breuer reflexes help control respirations by regulating depth of Hering-Breuer reflexes help control respirations by regulating depth of respirations and volume of tidal airrespirations and volume of tidal air

Cerebral cortex influences breathing by increasing or decreasing rate Cerebral cortex influences breathing by increasing or decreasing rate and strength of respirationsand strength of respirations


Regulation of Pulmonary FunctionRegulation of Pulmonary Function

Ventilation and perfusion (Figure 24-32)Ventilation and perfusion (Figure 24-32)

Alveolar ventilation—air flow to the alveoliAlveolar ventilation—air flow to the alveoli

Alveolar perfusion—blood flow to the alveoliAlveolar perfusion—blood flow to the alveoli

Efficiency of gas exchange can be maintained by Efficiency of gas exchange can be maintained by limited ability to match perfusion to ventilation—for limited ability to match perfusion to ventilation—for example, vasoconstricting arterioles that supply example, vasoconstricting arterioles that supply poorly ventilated alveoli and allow full blood flow to poorly ventilated alveoli and allow full blood flow to well-ventilated alveoliwell-ventilated alveoli


The Big Picture: The Big Picture: Respiratory System and the Whole BodyRespiratory System and the Whole Body

The internal system must continually get new oxygen and rid The internal system must continually get new oxygen and rid itself of carbon dioxide because each cell requires oxygen and itself of carbon dioxide because each cell requires oxygen and produces carbon dioxide as a result of energy conversionproduces carbon dioxide as a result of energy conversion

Specific mechanisms involved in respiratory function:Specific mechanisms involved in respiratory function: Blood gases need blood and the cardiovascular system to be Blood gases need blood and the cardiovascular system to be

transported between gas exchange tissues of lungs and various transported between gas exchange tissues of lungs and various systemic tissues of bodysystemic tissues of body

Regulation by the nervous system adjusts ventilation to compensate for Regulation by the nervous system adjusts ventilation to compensate for changes in oxygen or carbon dioxide levels in internal environmentchanges in oxygen or carbon dioxide levels in internal environment

Skeletal muscles of the thorax aid airways in maintaining flow of fresh airSkeletal muscles of the thorax aid airways in maintaining flow of fresh air

Skeleton houses the lungs, and the arrangement of bones facilitates the Skeleton houses the lungs, and the arrangement of bones facilitates the expansion and recoil of the thoraxexpansion and recoil of the thorax

Immune system prevents pathogens from colonizing the respiratory tract Immune system prevents pathogens from colonizing the respiratory tract and causing infectionand causing infection

chapter 24 physiology of the respiratory system

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