Rspiratory System (1)

8/13/2019 Rspiratory System (1)

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Chapter 23

The Respiratory

System


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Copyright John Wiley & Sons, Inc. All rights reserved.

Upperrespiratorytract

Lowerrespiratorytract

Respiratory System Anatomy

Structurally, the respiratory system is divided intoupper and lower divisions or tracts.

The upper respiratory tractconsists of the nose, pharynxand associated structures.

The lower respiratory tractconsists of the larynx,

trachea, bronchi and

lungs.


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Functionally,the respiratory system is divided into theconducting zone and the respiratory zone.

The conducting zone is involved with bringing air tothe site of external respiration and consists of the

nose, pharynx, larynx, trachea, bronchi,

bronchioles and terminal bronchioles.

The respiratory zone is the main site of gas exchangeand consists of the respiratory bronchioles, alveolar

ducts, alveolar sacs, and alveoli.


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The external nose is visible on the face.The internal nose is a large cavity beyond the nasalvestibule.

The internal nasal

cavity is

divided by a

nasal septum into

right and

left nares.



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Three nasal conchae or turbinates) protrude from eachlateral wall into the breathing passages.

Tucked under each nasal concha is an opening, or

meatus, for a duct that drains secretions of the sinusesand tears into the nose.

Receptors in the

olfactory epithelium

pierce the bone

of the cribriform plate.



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The pharynxis a hollow tube that starts posterior tothe internal nares and descends to the opening of the

larynx in the neck.

It is formed by a complex arrangement of skeletal

muscles that assist in deglutition.

It functions as:

o a passageway for air and food

o a resonating chamber

o a housing for the tonsils


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The nasopharynxlies behind the internal nares.It contains the pharyngeal tonsils (adenoids) and the

openings of the

Eustachian tubes

(auditory tubes)

which come off

of it and travels

to the middle

ear cavity.





The oropharynxlies behind the mouth and participatesin both respiratory and digestive functions.

The main palatine tonsils (those usually taken in a

tonsillectomy) and small lingual tonsil are housed

here.

The laryngopharynxlies inferiorly and opens into thelarynx (voice box) and the esophagus.

It participates in both respiratory and digestive

functions.




The larynx, composed of 9 pieces of cartilage, forms ashort passageway connecting the laryngopharynx with

the trachea (the windpipe).

The thyroid cartilage (the large

Adams apple) and the one below

it (the cricoid cartilage) are

landmarks for making an

emergency airway (called a

cricothyrotomy).Anterior view of the larynx



The epiglottisis a flap of elastic cartilage covered with amucus membrane, attached to the root of the tongue.

The epiglottis guards the entrance of the glottis, theopening between the vocal folds.

o For breathing, it is held

anteriorly, then pulled back-

ward to close off the glottic

opening during

swallowing.



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The rima glottidis (glottic opening) is formed by a pair ofmucous membrane vocal folds the true vocal cords).

The vocal folds are situated high in the larynx just

below where the larynx and the esophagus split off

from the pharynx.


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Cilia in the upper respiratory tract move mucous andtrapped particles down toward the pharynx.

Cilia in the lower respiratory tract move them up toward

the larynx.



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Upperrespiratorytract

Lowerrespiratorytract


As air passes from the laryngopharynx into the larynx, itleaves the upper respiratory tract and enters the lowerrespiratory tract.

Air passing through the respiratorytract

Nasal cavityPharynxLarynxTracheaPrimary bronchiSecondary bronchiTertiary bronchiBronchiolesAlveoli 150 million/lung)


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The tracheais a semi-rigid pipe made of semi-circularcartilaginous rings, and located anterior to the esophagus.

It is about 12 cm long and extends from the inferior

portion of the larynx into the mediastinum where it

divides into right and left primary (1o, mainstem)bronchi.

It is composed of 4 layers: a mucous secreting epithelium

called the mucosa, and three layers of CT (submucosa,hyaline cartilage, andadventitia).


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The tracheal cartilage rings are incomplete posteriorly,facing the esophagus.

Esophageal masses can press into this soft part of the

trachea and make it difficult

to breath, or even

totally obstruct

the airway.



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The right and left primary(1o or mainstem) bronchiemerge from the inferior trachea to go to the lungs,

situated in the right and left pleural cavities.

The carinais an internalridge located at the junction

of the two mainstem

bronchi a very sensitive

area for triggering thecough reflex.


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The 1obronchidivide to form 2oand 3obronchi whichrespectively supply the lobes and segments of each lung.

3obronchi divide into

bronchioleswhich inturn branch through

about 22 more divisions

(generations).

o The smallest are the

terminal bronchioles.


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The bronchi and bronchioles go through structural

changes as they branch and become smaller.

The mucous membrane changes and then disappears.

The cartilaginous rings become more sparse, andeventually disappear altogether.

As cartilage decreases, smooth muscle (under thecontrol of the Autonomic Nervous System) increases.

o Sympathetic stimulation causes airway dilation,while parasympathetic stimulation causes airwayconstriction.


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All the branches from the trachea to the terminalbronchioles are conductingairways they do notparticipate in gas

exchange.


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Respiratory bronchioles give way to alveolar ducts, andthe epithelium (simple cuboidal) changes to simplesquamous, which comprises the alveolar ducts, alveolarsacs, and alveoli.


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Taken together, these structures form the functional unitof the lung, which is the pulmonary lobule.

Wrapped in elastic

C.T., each pulmonary

lobule contains a

lymphatic vessel, an

arteriole, a venule

and a terminal

bronchiole.The pulmonary lobule



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As part of the pulmonary lobule, alveoli are delicatestructures composed chiefly of type I alveolar cells,which allow for exchange of gases with

the pulmonary capillaries.Alveoli make up a large

surface area (750 ft2).Type II cellssecrete asubstance called surfactantthat prevents collapse of the

alveoli during exhalation.


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Alveoli macrophages (also called dust cells) scavengethe alveolar surface to engulf and remove microscopic

debris that has made it past the mucociliary blanket

that traps most foreign particles higher inthe respiratory tract.

The alveoli (in close proximity

to the capillaries) form thealveolar-capillary membraneAC membrane).


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Blood Supply to the Lungs

The lungs receive blood via two sets of arteriesPulmonary arteriescarry deoxygenated blood from

the right heart to the lungs for oxygenation

Bronchial arteriesbranch from the aorta and

deliver oxygenated blood to the lungs primarily

perfusing the muscular walls of the bronchi andbronchioles


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Ventilation-Perfusion Coupling

Ventilation-perfusion coupling is the coupling ofperfusion (blood flow) to each area of he lungs to match

the extent of ventilation (airflow) to alveoli in that area

In the lungs, vasoconstriction in response to hypoxia

diverts pulmonary blood from poorly ventilated areas of

the lungs to well-ventilated regions

In all other body tissues, hypoxia causes dilation of blood

vessels to increase blood flow


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As organs, the lungs are divided into lobes by fissures.The right lung is divided by the oblique fissure and

the horizontal fissure into 3 lobes .The left lung is divided into

2 lobes by the oblique fissure.Each lobe receives it own 2obronchus that branches into

3osegmental bronchi (whichcontinue to further divide).



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The apexof the lung is superior, and extends slightlyabove the clavicles. The baseof thelungs rests on the diaphragm.

The cardiac notch in the left lung (the

indentation for the

heart) makes the leftlung 10 % smaller

than the right lung.



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On each side of the thorax, a pleural cavity is formed.The integrity of this space (really potential space)

between the parietal and visceral pleural layers is

crucial to the mechanism of breathing.

o Pleural fluid reduces friction and produces a surface

tension so the layers can slide across one another.

The pleura, adherent to the chest wall and to the lung,

produces a mechanical coupling for the two layers tomove together.

U d t di G


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Understanding Gases

To understand how this mechanical coupling betweenthe lungs, the pleural cavities and the chest wall results

in breathing, we first need to discuss some physics ofgases called thegas laws.


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Understanding Gases

The respiratory system depends on the medium of theearths atmosphere to extract the oxygen necessary forlife.

The atmosphere is composed of these gases:Nitrogen (N2) 78%

Oxygen (O2) 21%

Carbon Dioxide (CO2) 0.04%

Water Vapor variable, but on average

around 1%


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Understanding Gases

The gases of the atmosphere have a mass and a weight(5 x1018kg, most within 11 km of the surface).

Consequently, the atmosphere exerts a significant

force on every object on the planet (recall that

pressure is measured as force applied per unit area,

P = F/A.)

We are accustomed to the tremendous force

pressing down on every square inch of our body.


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Understanding Gases

A barometer is aninstrument that measures

atmospheric pressure.

Baro = pressure or weight

Meter = measure

Air pressure varies greatlydepending on the altitude

and the temperature.


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Understanding Gases

Boyles law applies to containers with flexible walls likeour thoracic cage.

It says that volume and pressure are inversely related.

o If there is a decrease in volume there will be anincrease in pressure.

o V 1/P


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Gas Exchange


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Gas Exchange

Gas Exchange

You must be connected to the internet to run this animation
http://www.wiley.com/college/tortora/0470084715/animations/anim_gas_exch/screen0.swfhttp://www.wiley.com/college/tortora/0470084715/animations/anim_gas_exch/screen0.swf


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Understanding Gases

Henrys law deals with gases and solutions.It says that increasing the partial pressure of a gas

over (in contact with) a solution will result in more

of the gas dissolving into the solution.The patient in this picture is getting

more O2in contact with his

blood - consequently,more oxygen goes

into his blood.Medicimage/Phototake

Understanding Gases


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Understanding Gases

Gas will always move from a region of high pressure to aregion of low pressure. Applying Boyle's law: If the

volume inside the thoracic cavity , the pressure .
http://www.wiley.com/college/jenkins/0470227583/animations/ch19/index_19_05_01.htmlhttp://www.wiley.com/college/jenkins/0470227583/animations/ch19/index_19_05_01.html


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Ventilation and Respiration

Pulmonary ventilationis the movement of air betweenthe atmosphere and the alveoli, and consists of inhalationand exhalation.

Ventilation, orbreathing, is made

possible by changes

in the intrathoracic

volume.


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In contrast to ventilation, respirationis the exchange of gases.

Externalrespiration(pulmonary)is gas exchange between thealveoli and the blood.

Internalrespiration(tissue)is gas exchange between

the systemic capillaries and

the tissues of the body.

l d


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External respiration in the lungs is possible because ofthe implications of Boyles law: The volume of the

thoracic cavity can be increased or decreased by the

action of the diaphragm, and other muscles of the chest

wall.

By changing the volume of the thoracic cavity (andthe lungs remember the mechanical coupling of the

chest wall, pleura, and lungs), the pressure in the lungswill also change.

il i d i i


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Changes in air pressure result in movement of the air.Contraction of the diaphragm and external intercostal

(rib) muscles increases the size of the thorax. This

decreases the intrapleural pressure so air can flow infrom the atmosphere (inspiration).

Relaxation of the diaphragm, with/without

contraction of the internal intercostals, decreases the

size of the thorax, increases the air pressure, and

results in exhalation.

V il i d R i i


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Certain thoracic

muscles participate in

inhalation; others aid

exhalation.

The diaphragm is

the primary muscle

of respiration all

the others are

accessory.

V il i d R i i


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The recruitment of accessory muscles greatly depends onwhether the respiratory movements are quiet (normal),or forced (labored).



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Ventilation and Respiration(Interactions Animation)

In the following animation, the mechanical couplingmechanism can be understood by relating the concepts

of the gas laws to the unique anatomical features of the

airways, pleural cavities, and muscles of respiration.

You must be connected to the internet to run this animation

Pulmonary Ventilation

Ai fl d W k f B thi
http://www.wiley.com/college/tortora/0470084715/animations/anim_pulm_vent/screen0.swfhttp://www.wiley.com/college/tortora/0470084715/animations/anim_pulm_vent/screen0.swf


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Airflow and Work of Breathing

Differences in air pressure drive airflow, but 3 otherfactorsalso affect the ease with which we ventilate:1. The surface tension of alveolar fluid causes the alveoli

to assume the smallest possible diameter and accountsfor 2/3 of lung elastic recoil. Normally the alveoli

would close with each expiration and make our

Work of Breathinginsupportable.o Surfactant prevents the complete collapse of alveoli

at exhalation, facilitating reasonable levels of work.

Ai fl d W k f B thi


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2. High lung compliance means the lungs and chest wallexpand easily.

Compliance is decreased by a

broken rib, or by diseases suchas pneumonia or emphysema.

Ai fl d W k f B thi


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M i V til ti


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Measuring Ventilation

Spirometry continuedVital Capacity VC) is all the air that can be exhaledafter maximum inspiration.

o It is the sum of the inspiratory reserve + tidalvolume + expiratory reserve (4800 ml).

Residual Volume RV) is the air still present in thelungs after a force exhalation (1200 ml).

o The RV is a reserve for mixing of gases but is not

available to move in or out of the lungs.

M i V til ti


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Old and new spirometers used to measure ventilation.

M i V til ti


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A graph of spirometer volumes and capacities

M i V til ti


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Only about 70% of the tidal volume reaches therespiratory zone the other 30% remains in the

conducting zone (called the anatomic dead space).If a single VT breath = 500 ml, only 350 ml will

exchange gases at the alveoli.

o In this example, with a respiratory rate of 12, the

minute ventilation = 12 x 500 = 6000 ml.o The alveolar ventilation (volume of air/min that

actually reaches the alveoli) = 12 x 350 = 4200ml.

E h f O d CO


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Exchange of O2and CO2

Using the gas laws and understanding the principals ofventilation and respiration,

we can calculate the

amount of oxygen andcarbon dioxide

exchanged between

the lungs and

the blood.

Exchange of O and CO


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Daltons Law states that each gas in a mixture of gasesexerts its own pressure as if no other gases were present.

The pressure of a specific gas is the partial pressure Pp.Total pressure is the sum of all the partial pressures.Atmospheric pressure (760 mmHg) = PN2+ PO2+ PH2O+ PCO2+ Pother gaseso Since O2is 21% of the atmosphere, the PO2is

760 x 0.21 = 159.6 mmHg.



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Each gas diffuses across a permeable membrane (like theAC membrane) from the side where its partial pressure is

greater to the side where its partial pressure is less.

The greater the difference, the faster the rate ofdiffusion.

Since there is a higher PO2on the lung side of the ACmembrane, O2moves from the alveoli into the blood.Since there is a higher PCO2on the blood side of the

AC membrane, CO2moves into the lungs.



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PN2 = 0.786 x 760 mmHg = 597.4 mmHg

PO2 = 0.209 x 760 mmHg = 158.8 mmHg

PH2O = 0.004 x 760 mmHg = 3.0 mmHgPCO2 = 0.0004 x 760 mmHg = 0.3 mmHg

Pother gases = 0.0006 x 760 mmHg = 0.5 mmHgTotal = 760.0 mmHg

Partial pressures of gases in inhaled air for sea level



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Henrys law states that the quantity of a gas that willdissolve in a liquid is proportional to the partial pressures

of the gas and its solubility.

A higher partial pressure of agas (like O2) over a liquid (likeblood) means more of the gas

will stay in solution.

Because CO2 is 24 times more soluble in blood (andsoda pop!) than in O2, itmore readily dissolves.



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Even though the air we breathe is mostly N2, very littledissolves in blood due to its low solubility.

Decompression sickness (the bends) is a result of the

comparatively insoluble N2being forcedto dissolveinto the blood and tissues because of the very high

pressures associated with diving.

o By ascending too rapidly, the N2rushes out of thetissues and the blood so forcefully as to cause vessels

to pop and cells to die.

Transport of O and CO


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Transport of O2and CO2

In the blood, some O2is dissolved in the plasma as a gas(about 1.5%, not enough to stay alive not by a long

shot!). Most O2(about 98.5%) is carried attached to Hb.Oxygenated Hb is called oxyhemoglobin.



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CO2is transported in the blood in three different forms:1. 7% is dissolved in the plasma, as a gas.2. 70% is converted into carbonic acid through the

action of an enzyme called carbonic anhydrase.

o CO2+ H2O H2CO3 H++ HCO3-3. 23% is attached to Hb (but not at the same binding

sites as oxygen).



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The O2transported in the blood (PO2= 100 mmHg) isneeded in the tissues to continually make ATP (PO2= 40mmHg at the capillaries).

CO2constantly diffusesfrom the tissues(PCO2= 45 mmHg) to

be transported inthe blood

(PCO2= 40 mmHg) Internal Respiration occurs atsystemic capillaries


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Transport of O2 and CO2


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The relationship between the amount of O2dissolved inthe plasma and the saturation of Hb is called the oxygen-hemoglobin saturation curve.

The higher the PO2dissolved in the plasma,

the higher the SaO2.



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Measuring SaO2hasbecome as commonplace

in clinical practice as

taking a blood pressure.

Pulse oximeters whichused to cost $5,000can now be purchased

at your local

pharmacy.3660 Group,

Inc/NewsCom



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Although PO2is the most important determinant of SaO2,

several other factors influence the affinity with which

Hb binds O2.

Acidity (pH), PCO2and blood temperature shift theentire O2 Hb saturationcurve either to the left

(higher affinity for O2), orto the right (lower affinity

for O2).



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As blood flows from the lungs toward the tissues, theincreasing acidity (pH decreases) shifts the O2Hbsaturation curve to the right, enhancing unloading of

O2(which is just what we want to happen).This is called the Bohr effect.

At the lungs, oxygenated blood has a reduced capacity

to carry CO2,and it is unloaded as we exhale (also justwhat we want to happen).

This is called the Haldane effect.

Fetal and Maternal Hemoglobin


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Fetal and Maternal Hemoglobin

Fetal hemoglobin (Hb-F) has a higher affinity for oxygen(it is shifted to the left) than adult hemoglobin A, so it

binds O2 more strongly.

The fetus is thus ableto attract oxygen

across the placenta

and support life,

without lungs.

Control of Respiration


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The medulla rhythmicity area, located in the brainstem,has centers that control basic respiratory patterns for both

inspiration and expiration.

The inspiratory centerstimulates the diaphragm

via the phrenic nerve, and

the external intercostal

muscle via intercostal nerves.

o Inspiration normally lasts about 2 sec.



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Other sites in the pons help the medullary centers manage

the transition between inhalation and exhalation.

The pneumotaxic center limits inspiration to preventhyperexpansion.

The apneustic

center coordinates

the transition between

inhalation and exhalation.



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Other brain areas also play a role in respiration:Our cortexhas voluntary control of breathing.Stretch receptors sensing over-inflation arrests

breathing temporarily Herring Breuer reflex).Emotions(limbic system) affect respiration.The hypothalamus, sensing a fever, increasesbreathing, as does moderate pain(severe pain causesapnea.)


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Response to Pollutants


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Initial ResponseMucous layer thickens.

Goblet cells over-secrete

mucous.

Basal cells proliferate.

Advanced Response to IrritationMucous layer and goblet cells disappear.

Basal cells become malignant & invade deeper tissue.

Normal columnar epithelium

in the respiratory tract

Response to Pollutants

Diseases and Disorders


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Asthmais a disease of hyper-reactive airways (the majorabnormality is constriction of smooth muscle in the

bronchioles, and inflammation.) It presents as attacks of

wheezing, coughing, and excess mucus production.It typically occurs in response to allergens; less often

to emotion.

Bronchodilators and anti-

inflammatory corticosteroids

are mainstays of treatment.

Pulse Picture Library/CMP mages /Phototake



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Chronic bronchitis and emphysemaare caused bychronic irritation and inflammation leading to lung

destruction. Patients may cough up

green-yellow sputum due toinfection and increased mucous

secretion (productive cough).

They are almost exclusively

diseases of cigarette smoking.



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Pneumoniais an acute infection of the lowest parts ofthe respiratory tract.

The small bronchioles and alveoli become filled with

an inflammatory fluid exudate.o It is typically caused by infectious agents such as

bacteria, viruses, or fungi.



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Normal Lungs Pneumonia Patient

Du Cane Medical Imaging, Ltd./Photo Researchers, Inc

End of Chapter 23


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End of Chapter 23

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Rspiratory System (1)