Chapter 23The Respiratory System

• Cells continually use O2 & release CO2

• Respiratory system designed for gas exchange

• Cardiovascular system transports gases in blood

• Failure of either system– rapid cell death from O2

starvation

Respiratory System Anatomy• Nose• Pharynx = throat• Larynx = voicebox• Trachea = windpipe• Bronchi = airways• Lungs• Locations of infections

– upper respiratory tract is above vocal cords

– lower respiratory tract is below vocal cords

External Nasal Structures

• Skin, nasal bones, & cartilage lined with mucous membrane• Openings called external nares or nostrils

Nose -- Internal Structures

• Large chamber within the skull• Roof is made up of ethmoid and floor is hard palate• Internal nares (choanae) are openings to pharynx• Nasal septum is composed of bone & cartilage• Bony swelling or conchae on lateral walls

Functions of the Nasal Structures

• Olfactory epithelium for sense of smell

• Pseudostratified ciliated columnar with goblet cells lines nasal cavity– warms air due to high vascularity– mucous moistens air & traps dust– cilia move mucous towards pharynx

• Paranasal sinuses open into nasal cavity– found in ethmoid, sphenoid, frontal & maxillary– lighten skull & resonate voice

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Rhinoplasty

• Commonly called a “nose job”• Surgical procedure done for cosmetic

reasons / fracture or septal repair• Procedure

– local and general anesthetic– nasal cartilage is reshaped through nostrils– bones fractured and repositioned– internal packing & splint while healing

Pharynx • Muscular tube (5 inch long) hanging from

skull– skeletal muscle & mucous membrane

• Extends from internal nares to cricoid cartilage

• Functions– passageway for food and air– resonating chamber for speech production– tonsil (lymphatic tissue) in the walls protects

entryway into body

• Distinct regions -- nasopharynx, oropharynx and laryngopharynx

Nasopharynx

• From choanae to soft palate– openings of auditory (Eustachian) tubes from middle ear cavity

– adenoids or pharyngeal tonsil in roof

• Passageway for air only– pseudostratified ciliated columnar epithelium with goblet

Oropharynx

• From soft palate to epiglottis– fauces is opening from mouth into oropharynx

– palatine tonsils found in side walls, lingual tonsil in tongue

• Common passageway for food & air– stratified squamous epithelium

Laryngopharynx

• Extends from epiglottis to cricoid cartilage

• Common passageway for food & air & ends as esophagus inferiorly– stratified squamous epithelium

Cartilages of the Larynx

• Thyroid cartilage forms Adam’s apple

• Epiglottis---leaf-shaped piece of elastic cartilage– during swallowing, larynx moves upward– epiglottis bends to cover glottis

• Cricoid cartilage---ring of cartilage attached to top of trachea

• Pair of arytenoid cartilages sit upon cricoid– many muscles responsible for their movement– partially buried in vocal folds (true vocal cords)

Larynx

• Cartilage & connective tissue tube• Anterior to C4 to C6• Constructed of 3 single & 3 paired cartilages

Vocal Cords

• False vocal cords (ventricular folds) found above vocal folds (true vocal cords)

• True vocal cords attach to arytenoid cartilages

The Structures of Voice Production

• True vocal cord contains both skeletal muscle and an elastic ligament (vocal ligament)

• When 10 intrinsic muscles of the larynx contract, move cartilages & stretch vocal cord tight

• When air is pushed past tight ligament, sound is produced (the longer & thicker vocal cord in male produces a lower pitch of sound)

• The tighter the ligament, the higher the pitch

• To increase volume of sound, push air harder

Movement of Vocal Cords

• Opening and closing of the vocal folds occurs during breathing and speech

Speech and Whispering

• Speech is modified sound made by the larynx.

• Speech requires pharynx, mouth, nasal cavity & sinuses to resonate that sound

• Tongue & lips form words

• Pitch is controlled by tension on vocal folds– pulled tight produces higher pitch– male vocal folds are thicker & longer so vibrate

more slowly producing a lower pitch

• Whispering is forcing air through almost closed rima glottidis -- oral cavity alone forms speech

Trachea• Size is 5 in long & 1in diameter

• Extends from larynx to T5 anterior to the esophagus and then splits into bronchi

• Layers– mucosa = pseudostratified columnar with cilia & goblet– submucosa = loose connective tissue & seromucous glands– hyaline cartilage = 16 to 20 incomplete rings

• open side facing esophagus contains trachealis m. (smooth)• internal ridge on last ring called carina

– adventitia binds it to other organs

Trachea and Bronchial Tree

• Full extent of airways is visible starting at the larynx and trachea

Histology of the Trachea

• Ciliated pseudostratified columnar epithelium • Hyaline cartilage as C-shaped structure closed by

trachealis muscle

Airway Epithelium

• Ciliated pseudostratified columnar epithelium with goblet cells produce a moving mass of mucus.

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Tracheostomy and Intubation

• Reestablishing airflow past an airway obstruction– crushing injury to larynx or chest– swelling that closes airway– vomit or foreign object

• Tracheostomy is incision in trachea below cricoid cartilage if larynx is obstructed

• Intubation is passing a tube from mouth or nose through larynx and trachea

Bronchi and Bronchioles

• Primary bronchi supply each lung

• Secondary bronchi supply each lobe of the lungs (3 right + 2 left)

• Tertiary bronchi supply each bronchopulmonary segment

• Repeated branchings called bronchioles form a bronchial tree

Histology of Bronchial Tree• Epithelium changes from pseudostratified ciliated

columnar to nonciliated simple cuboidal as pass deeper into lungs

• Incomplete rings of cartilage replaced by rings of smooth muscle & then connective tissue– sympathetic NS & adrenal gland release epinephrine that

relaxes smooth muscle & dilates airways– asthma attack or allergic reactions constrict distal

bronchiole smooth muscle– nebulization therapy = inhale mist with chemicals that

relax muscle & reduce thickness of mucus

Pleural Membranes & Pleural Cavity

• Visceral pleura covers lungs --- parietal pleura lines ribcage & covers upper surface of diaphragm

• Pleural cavity is potential space between ribs & lungs

Gross Anatomy of Lungs

• Base, apex (cupula), costal surface, cardiac notch• Oblique & horizontal fissure in right lung results in 3 lobes• Oblique fissure only in left lung produces 2 lobes

Mediastinal Surface of Lungs

• Blood vessels & airways enter lungs at hilus• Forms root of lungs• Covered with pleura (parietal becomes visceral)

Structures within a Lobule of Lung

• Branchings of single arteriole, venule & bronchiole are wrapped by elastic CT

• Respiratory bronchiole– simple squamous

• Alveolar ducts surrounded by alveolar sacs & alveoli– sac is 2 or more alveoli sharing

a common opening

Photomicrograph of lung tissue showing bronchioles, alveoli and alveolar ducts.

Histology of Lung Tissue

Cells Types of the Alveoli

• Type I alveolar cells– simple squamous cells where gas exchange occurs

• Type II alveolar cells (septal cells)– free surface has microvilli– secrete alveolar fluid containing surfactant

• Alveolar dust cells– wandering macrophages remove debris

Alveolar-Capillary Membrane

• Respiratory membrane = 1/2 micron thick• Exchange of gas from alveoli to blood• 4 Layers of membrane to cross

– alveolar epithelial wall of type I cells– alveolar epithelial basement membrane– capillary basement membrane– endothelial cells of capillary

• Vast surface area = handball court

Details of Respiratory Membrane

• Find the 4 layers that comprise the respiratory membrane

Double Blood Supply to the Lungs

• Deoxygenated blood arrives through pulmonary trunk from the right ventricle

• Bronchial arteries branch off of the aorta to supply oxygenated blood to lung tissue

• Venous drainage returns all blood to heart

• Less pressure in venous system

• Pulmonary blood vessels constrict in response to low O2 levels so as not to pick up CO2 on there way through the lungs

Breathing or Pulmonary Ventilation

• Air moves into lungs when pressure inside lungs is less than atmospheric pressure– How is this accomplished?

• Air moves out of the lungs when pressure inside lungs is greater than atmospheric pressure– How is this accomplished?

• Atmospheric pressure = 1 atm or 760mm Hg

Boyle’s Law

• As the size of closed container decreases, pressure inside is increased

• The molecules have less wall area to strike so the pressure on each inch of area increases.

Dimensions of the Chest Cavity

• Breathing in requires muscular activity & chest size changes• Contraction of the diaphragm flattens the dome and

increases the vertical dimension of the chest

• Diaphragm moves 1 cm & ribs lifted by muscles• Intrathoracic pressure falls and 2-3 liters inhaled

Quiet Inspiration

• Passive process with no muscle action• Elastic recoil & surface tension in alveoli pulls inward• Alveolar pressure increases & air is pushed out

Quiet Expiration

Labored Breathing

• Forced expiration– abdominal mm force

diaphragm up– internal intercostals

depress ribs

• Forced inspiration– sternocleidomastoid,

scalenes & pectoralis minor lift chest upwards as you gasp for air

IntrathoracicPressures

• Always subatmospheric (756 mm Hg)

• As diaphragm contracts intrathoracic pressure decreases even more (754 mm Hg)

• Helps keep parietal & visceral pleura stick together

Summary of Breathing

• Alveolar pressure decreases & air rushes in• Alveolar pressure increases & air rushes out

Alveolar Surface Tension• Thin layer of fluid in alveoli causes

inwardly directed force = surface tension– water molecules strongly attracted to each other

• Causes alveoli to remain as small as possible

• Detergent-like substance called surfactant produced by Type II alveolar cells – lowers alveolar surface tension– insufficient in premature babies so that alveoli

collapse at end of each exhalation

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Pneumothorax

• Pleural cavities are sealed cavities not open to the outside

• Injuries to the chest wall that let air enter the intrapleural space– causes a pneumothorax– collapsed lung on same side as injury – surface tension and recoil of elastic fibers

causes the lung to collapse

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Compliance of the Lungs

• Ease with which lungs & chest wall expand depends upon elasticity of lungs & surface tension

• Some diseases reduce compliance– tuberculosis forms scar tissue– pulmonary edema --- fluid in lungs & reduced

surfactant– paralysis

Airway Resistance

• Resistance to airflow depends upon airway size– increase size of chest

• airways increase in diameter

– contract smooth muscles in airways• decreases in diameter

Breathing Patterns

• Eupnea = normal quiet breathing

• Apnea = temporary cessation of breathing

• Dyspnea =difficult or labored breathing

• Tachypnea = rapid breathing

• Diaphragmatic breathing = descent of diaphragm causes stomach to bulge during inspiration

• Costal breathing = just rib activity involved

Modified Respiratory Movements

• Coughing– deep inspiration, closure of rima glottidis & strong

expiration blasts air out to clear respiratory passages

• Hiccuping– spasmodic contraction of diaphragm & quick

closure of rima glottidis produce sharp inspiratory sound

• Chart of others on page 794

• Tidal volume = amount air moved during quiet breathing• MVR= minute ventilation is amount of air moved in a minute• Reserve volumes ---- amount you can breathe either in or out above that

amount of tidal volume• Residual volume = 1200 mL permanently trapped air in system• Vital capacity & total lung capacity are sums of the other volumes

Lung Volumes and Capacities

Dalton’s Law

• Each gas in a mixture of gases exerts its own pressure– as if all other gases were not present– partial pressures denoted as p

• Total pressure is sum of all partial pressures– atmospheric pressure (760 mm Hg) = pO2 + pCO2

+ pN2 + pH2O– to determine partial pressure of O2-- multiply 760

by % of air that is O2 (21%) = 160 mm Hg

What is Composition of Air?

• Air = 21% O2, 79% N2 and .04% CO2

• Alveolar air = 14% O2, 79% N2 and 5.2% CO2

• Expired air = 16% O2, 79% N2 and 4.5% CO2

• Observations– alveolar air has less O2 since absorbed by blood– mystery-----expired air has more O2 & less CO2 than

alveolar air?– Anatomical dead space = 150 ml of 500 ml of tidal volume

Henry’s Law

• Quantity of a gas that will dissolve in a liquid depends upon the amount of gas present and its solubility coefficient– explains why you can breathe compressed air while

scuba diving despite 79% Nitrogen• N2 has very low solubility unlike CO2 (soda cans)

• dive deep & increased pressure forces more N2 to dissolve in the blood (nitrogen narcosis)

• decompression sickness if come back to surface too fast or stay deep too long

• Breathing O2 under pressure dissolves more O2 in blood

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Hyperbaric Oxygenation• Clinical application of Henry’s law

• Use of pressure to dissolve more O2 in the blood– treatment for patients with anaerobic bacterial

infections (tetanus and gangrene)– anaerobic bacteria die in the presence of O2

• Hyperbaric chamber pressure raised to 3 to 4 atmospheres so that tissues absorb more O2

• Used to treat heart disorders, carbon monoxide poisoning, cerebral edema, bone infections, gas embolisms & crush injuries

External Respiration• Gases diffuse from areas

of high partial pressure to areas of low partial pressure

• Exchange of gas between air & blood

• Deoxygenated blood becomes saturated

• Compare gas movements in pulmonary capillaries to tissue capillaries

Rate of Diffusion of Gases

• Depends upon partial pressure of gases in air– p O2 at sea level is 160 mm Hg– 10,000 feet is 110 mm Hg / 50,000 feet is 18 mm Hg

• Large surface area of our alveoli

• Diffusion distance is very small

• Solubility & molecular weight of gases– O2 smaller molecule diffuses somewhat faster– CO2 dissolves 24X more easily in water so net

outward diffusion of CO2 is much faster– disease produces hypoxia before hypercapnia

– lack of O2 before too much CO2

Internal Respiration• Exchange of gases between

blood & tissues

• Conversion of oxygenated blood into deoxygenated

• Observe diffusion of O2 inward– at rest 25% of available O2

enters cells– during exercise more O2 is

absorbed

• Observe diffusion of CO2 outward

Oxygen Transport in the Blood

• Oxyhemoglobin contains 98.5% chemically combined oxygen and hemoglobin– inside red blood cells

• Does not dissolve easily in water– only 1.5% transported dissolved in blood

• Only the dissolved O2 can diffuse into tissues

• Factors affecting dissociation of O2 from hemoglobin are important

• Oxygen dissociation curve shows levels of saturation and oxygen partial pressures

• Blood is almost fully saturated at pO2 of 60mm– people OK at high altitudes

& with some disease

• Between 40 & 20 mm Hg, large amounts of O2 are released as in areas of need like contracting muscle

Hemoglobin and Oxygen Partial Pressure

Acidity & Oxygen Affinity for Hb

• As acidity increases, O2 affinity for Hb decreases

• Bohr effect

• H+ binds to hemoglobin & alters it

• O2 left behind in needy tissues

pCO2 & Oxygen Release

• As pCO2 rises with exercise, O2 is released more easily

• CO2 converts to carbonic acid & becomes H+ and bicarbonate ions & lowers pH.

Temperature & Oxygen Release

• As temperature increases, more O2 is released

• Metabolic activity & heat

• More BPG, more O2 released– RBC activity– hormones like

thyroxine & growth hormone

Oxygen Affinity & Fetal Hemoglobin

• Differs from adult in structure & affinity for O2

• When pO2 is low, can carry more O2

• Maternal blood in placenta has less O2

Carbon Monoxide Poisoning

• CO from car exhaust & tobacco smoke

• Binds to Hb heme group more successfully than O2

• CO poisoning

• Treat by administering pure O2

Carbon Dioxide Transport

• 100 ml of blood carries 55 ml of CO2

• Is carried by the blood in 3 ways– dissolved in plasma– combined with the globin part of Hb molecule

forming carbaminohemoglobin– as part of bicarbonate ion

• CO2 + H2O combine to form carbonic acid that dissociates into H+ and bicarbonate ion

Summary of Gas Exchange & Transport

Role of the Respiratory Center

• Respiratory mm. controlled by neurons in pons & medulla

• 3 groups of neurons– medullary

rhythmicity– pneumotaxic– apneustic centers

Medullary Rhythmicity Area• Controls basic rhythm of respiration

• Inspiration for 2 seconds, expiration for 3

• Autorhythmic cells active for 2 seconds then inactive

• Expiratory neurons inactive during most quiet breathing only active during high ventilation rates

Pneumotaxic & Apneustic Areas

• Pneumotaxic Area– constant inhibitory impulses to inspiratory area

• neurons trying to turn off inspiration before lungs too expanded

• Apneustic Area– stimulatory signals to inspiratory area to

prolong inspiration– if pneumotaxic area is sick

Regulation of Respiratory Center

• Cortical Influences– voluntarily alter breathing patterns– limitations are buildup of CO2 & H+ in blood– inspiratory center is stimulated by increase in

either– if you hold breathe until you faint----breathing

will resume

Chemical Regulation of Respiration

• Central chemoreceptors in medulla– respond to changes in H+ or pCO2– hypercapnia = slight increase in pCO2 is noticed

• Peripheral chemoreceptors– respond to changes in H+ , pO2 or PCO2– aortic body---in wall of aorta

• nerves join vagus

– carotid bodies--in walls of common carotid arteries• nerves join glossopharyngeal nerve

• Negative feedback control of breathing

• Increase in arterial pCO2• Stimulates receptors• Inspiratory center• Muscles of respiration

contract more frequently & forcefully

• pCO2 Decreases

Negative Feedback Regulation of Breathing

Regulation of Ventilation Rate and Depth

Types of Hypoxia• Deficiency of O2 at tissue level

• Types of hypoxia– hypoxic hypoxia--low pO2 in arterial blood

• high altitude, fluid in lungs & obstructions

– anemic hypoxia--too little functioning Hb• hemorrhage or anemia

– ischemic hypoxia--blood flow is too low– histotoxic hypoxia--cyanide poisoning

• blocks metabolic stages & O2 usage

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Respiratory Influences & Reflex Behaviors

• Quick breathing rate response to exercise– input from proprioceptors

• Inflation Reflex (Hering-Breurer reflex)– big deep breath stretching receptors produces urge

to exhale

• Factors increasing breathing rate – emotional anxiety, temperature increase or drop in

blood pressure

• Apnea or cessation of breathing – by sudden plunge into cold water, sudden pain,

irritation of airway

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Exercise and the Respiratory System• During exercise, muscles consume large

amounts of O2 & produce large amounts CO2

• Pulmonary ventilation must increase– moderate exercise increases depth of breathing, – strenuous exercise also increases rate of breathing

• Abrupt changes at start of exercise are neural– anticipation & sensory signals from proprioceptors– impulses from motor cortex

• Chemical & physical changes are important– decrease in pO2, increase in pCO2 & increased

temperature

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Smokers Lowered Respiratory Efficiency

• Smoker is easily “winded” with moderate exercise– nicotine constricts terminal bronchioles– carbon monoxide in smoke binds to hemoglobin– irritants in smoke cause excess mucus secretion– irritants inhibit movements of cilia– in time destroys elastic fibers in lungs & leads to

emphysema• trapping of air in alveoli & reduced gas exchange

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Developmental Anatomy of Respiratory System

• 4 weeks endoderm of foregut gives rise to lung bud

• Differentiates into epithelial lining of airways

• 6 months closed-tubes swell into alveoli of lungs

Aging & the Respiratory System

• Respiratory tissues & chest wall become more rigid

• Vital capacity decreases to 35% by age 70.• Decreases in macrophage activity• Diminished ciliary action• Decrease in blood levels of O2• Result is an age-related susceptibility to

pneumonia or bronchitis

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Disorders of the Respiratory System• Asthma

• Chronic obstructive pulmonary disease– Emphysema– Chronic bronchitis– Lung cancer

• Pneumonia

• Tuberculosis

• Coryza and Influenza

• Pulmonary Edema

• Cystic fibrosis