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Respiratory System

• Major functions of respiratory system: supply body with O2 for cellular respiration and dispose of CO2, a waste product of cellular respiration

• Respiratory and circulatory system are closely coupled

• Also functions in olfaction and speech

Respiratory System

• Respiration involves four processes1. Pulmonary ventilation

(breathing): movement of air into and out of lungs

2. External respiration: exchangeof O2 and CO2 between lungs and blood

3. Transport of O2 and CO2 in blood

4. Internal respiration: exchange ofO2 and CO2 between systemic blood vessels and tissues

Circulatory

system

Respiratory

system

The Major Respiratory Organs

Nasal cavity

Nostril

Larynx

Trachea

Carina of trachea

Right main (primary) bronchus

Right lungDiaphragm

Left lung

Left main (primary) bronchus

Oral cavity

Pharynx

Conducting ZoneRespiratory Zone

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Anatomical Relationships Of Organs In The Thoracic Cavity

Trachea

Thymus

Apex of lung

Right superior lobe

Horizontal fissure

Right middle lobe

Oblique fissure

Right inferior lobe

Heart(in mediastinum)

Diaphragm

Base of lung Cardiac notch

Anterior view. The lungs flank mediastinal structures laterally.

Left inferiorlobe

Obliquefissure

Leftsuperior lobe

Visceral pleura

Pleural cavity

Parietal pleura

Rib

Intercostal muscle

Lung

Hilum of the LungApex of lung

Pulmonary artery

Left mainbronchus

Pulmonaryvein

Cardiacimpression

Obliquefissure

Lobules

Aorticimpression

Hilum of lung

Left inferiorlobe

Obliquefissure

Leftsuperior lobe

Photograph of medial view of the left lung.

Anatomical relationships of organs in the thoracic cavity

PosteriorVertebra

Right lung

Parietal pleura

Visceral pleura

Pleural cavity

Pericardial membranes

Anterior mediastinum

Anterior

Heart (in mediastinum)

Pulmonary trunk

Thoracic wall

Left lung

• Left pulmonary vein

• Left pulmonary artery

• Left main bronchus

Root of lungat hilum

Esophagus(in mediastinum)

Sternum

Transverse section through the thorax, viewed from above. Lungs, pleural membranes, and major organs in the mediastinum are shown.

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Nasal Cavity Posteriornasalaperture

Sphenoidalsinus

Frontal sinus

Nasal cavity

• Nasal conchae(superior, middle and inferior)

• Nasal meatuses(superior, middle, and inferior)

• Nasal vestibule

• Nostril

Hardpalate

TongueSoftpalate

Uvula

Cribriformplate ofethmoid bone

• Passageway• Moistens and warms entering air• Filters and cleans• Resonating chamber for speech• Location of olfactory receptors

• Vibrissae• Mucus membranes

• Pseudostratified ciliated epithelium• Goblet cells• Cilia – directed toward

pharynx• Seromucous glands: lysozyme• Defensins

Conchae:• Increase

surface area of mucosa

• Increase air turbulence

Pharynx, Larynx, and Upper Trachea

(b) Structures of the pharynx and larynx

Nasopharynx

Oropharynx

Larynx

Posterior nasalaperture

• Pharyngeal tonsil

• Opening ofpharyngotympanictube

• Palatine tonsil

• Isthmus of thefauces

Esophagus

Laryngopharynx

Trachea

Hard palate

Soft palate

Tongue

Lingual tonsil

Hyoid bone

• Epiglottis

• Vestibular fold

• Thyroid cartilage

• Vocal fold

• Cricoid cartilage

Thyroid gland

Air or Air and food passageway

‘Eustachian’ tube

Unencapsulatedlymphoid nodules

Epiglottis (elastic cartilage) protects airway (glottis) from food/drink during swallowing

The Larynx

Body of hyoid bone

Thyroid cartilage

Laryngeal prominence(Adam’s apple)

Cricothyroid ligament

Cricoid cartilage

Trachealcartilages

Anterior view

Thyrohyoidmembrane

Epiglottis

• Location of vocal folds typically known as the true vocal cords

• Airway – in and out – return to pseudostratified ciliated epithelium

• Voice production

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Epiglottis

Vestibular fold (false vocal cord)

Vocal fold (true vocal cord)

Glottis

Inner lining of trachea

Cuneiform cartilage

Corniculate cartilage

Movements of the vocal folds.

Vocal folds in closed position;closed glottis

Vocal folds in open position;open glottis

https://youtu.be/9Tlpkdq8a8c

Tissue Composition Of The Tracheal Wall

Esophagus

Trachealis

Posterior

Lumen of trachea

Anterior

Submucosa - glandular

Hyaline cartilage

Adventitia

Seromucous glandin submucosa

Mucosa – pseudostratified ciliated epithelium

• ‘Windpipe’• Supported by C – shaped rings of hyaline

cartilage – prevents closing even when thoracic pressure changes and food in esophagus pushes

• Carina

Tissue composition of the tracheal wall

Goblet cell

Mucosa

Pseudostratifiedciliated columnarepithelium

Lamina propria(connective tissue)

•

•

Submucosa

Seromucous glandin submucosa

Photomicrograph of thetracheal wall (320 )

Hyaline cartilage

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Conducting Zone Passages

Superior lobe of left lung

Lobar (secondary)bronchus

Left main(primary) bronchus

Segmental(tertiary)bronchus

Inferior lobeof left lung

Inferior lobe of right lung

Middle lobe of right lung

Superior lobe of right lung

Trachea

At level of T7

• Three lobes on right; two lobes on left• Segments• Lobules

• C-rings replaced by hyaline plates• Elastic tissue present - stroma• Pseudostratified ciliated eventually replaced by columnar• Smooth muscle in walls increases

Respiratory Zone Structures

Alveolar ductAlveoli

Alveolar duct

Alveolarsac

Terminalbronchiole

Respiratorybronchioles

• Terminal bronchioles <0.5 mm in diameter• No cartilage involvement• Smooth muscle dominates• Epithelium now non-ciliated cuboidal in the smallest tubes• Mucus production limited then ends

Respiratory Zone Structures

Respiratorybronchiole

Alveolarduct

Alveolarpores

Alveoli

Alveolarsac

Alveolar surface area = 90 m2 or 969 ft2 in healthy lungs of adult male

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Alveoli And The Respiratory Membrane

Respiratory bronchiole

Terminal bronchiole

Smoothmuscle

Elasticfibers

Alveolus

Capillaries

Respiratory membrane is combination of alveolar squamous cells and capillary endothelial cells • 0.5 µm thick blood-air barrier

Alveoli And The Respiratory Membrane

Alveolus

Capillary

Nucleus of type Ialv eolar cell

Alv eolar pores

Alv eolar epithelium

Endothelial cell nucleus

Respiratorymembrane

Alveolus

CapillaryO2

CO2

Fused basement membranesof alv eolar epithelium andcapillary endothelium

Capillary endothelium

Macrophage

Type Ialv eolar cell

Type II alv eolar cell(secretes surfactant)

Red blood cellin capillary

Alv eoli (gas-filledair spaces)

Detailed anatomy of the respiratory membrane

Red blood cell

• Type I alveolar cells = simple squamous supported by thin basement membrane, dominate• Type II alveolar cells = scattered surfactant-producing cuboidal cells, produce antimicrobials also.

Surfactant decreases cohesiveness (surface tension) of water on surface, reducing tendency to collapse

• Alveolar pores share air between adjacent alveoli• Alveolar macrophages move along surface eventually being swept out

Pulmonary Ventilation• Boyle’s law: relationship between pressure and

volume of a gas• Gases always fill the container they are in

• If amount of gas is the same and container size is reduced, pressure will increase

• So pressure (P) varies inversely with volume (V)

• Mathematically:• P1V1 = P2V2

When atmospheric pressure and intrapulmonary pressure are the same, no air moves• muscles acting on the lungs change the intrapulmonary

pressure

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Parietal pleura

Atmospheric pressure (Patm

)0 mm Hg (760 mm Hg at sea level)

Thoracicwall

Visceral pleura

Pleural cavity containing pleural fluid

Transpulmonarypressure4 mm Hg (the difference between 0

mm Hg and 4 mm Hg)

Must be maintained or lung collapses

Intrapleuralpressure (P

ip)

4 mm Hg(756 mm Hg)

Intrapulmonarypressure (P

pul)

0 mm Hg(760 mm Hg)

4

0

Diaphragm

LungStrong adhesive forces between visceral and parietal pleurae keeps Pip

negative

Sequence of eventsChanges in anterior-posterior and

superior-inferior dimensions

Changes in lateral dimensions(superior view)

Insp

ira

tio

nE

xp

ira

tio

n

Ribs areelev ated and sternum flaresas externalintercostals

contract.

Externalintercostalscontract.

Diaphragm movesinferiorly duringcontraction.

Ribs andsternum aredepressed asexternalintercostals

relax.

Externalintercostalsrelax.

Diaphragmmov essuperiorlyas it relaxes.

Inspiratory muscles contract(diaphragm descends; rib cagerises).

1

Thoracic cavity volumeincreases.2

Lungs are stretched;intrapulmonary volume increases.3

Intrapulmonary pressuredrops (to 1 mm Hg).4

Air (gases) flows into lungsdown its pressure gradient untilintrapulmonary pressure is 0(equal to atmospheric pressure).

5

Inspiratory muscles relax(diaphragm rises; rib cagedescends due to recoil of costalcartilages).

1

Thoracic cavity volumedecreases.2

Elastic lungs recoilpassively; intrapulmonaryv olume decreases.

3

Intrapulmonary pressure rises(to 1 mm Hg).4

Air (gases) flows out of lungsdown its pressure gradientuntil intrapulmonary pressure is 0.

5

• Normal inspirational muscle contractions lead to 500 ml change in volume

• Diaphragm is dominant inspirational muscle

Forced inspirations recruit the scalenes, sternocleidomastoids, pectoralis minors, and erector spinae

Normal expiration is passive

Gas Exchange:Basic Properties of Gases

• Dalton’s law of partial pressures• Total pressure exerted by mixture of gases is equal to sum of

pressures exerted by each gas

• Partial pressure• Pressure exerted by each gas in mixture

• Directly proportional to its percentage in mixture

• Henry’s law• For gas mixtures in contact with liquids:

• Each gas will dissolve in the liquid in proportion to its partial pressure

• At equilibrium, partial pressures in the two phases will be equal

• Amount of each gas that will dissolve depends on: • Solubility: CO2 is 20 more soluble in water than O2, and little N2 will

dissolve

• Temperature: as temperature of liquid rises, solubility decreases

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Partial Pressure Gradients Promoting Gas Movements In The Body

Inspired air: Alveoli of lungs:

External

respiration

Pulmonary

veins (PO2

100 mm Hg)

PO2

PCO2

160 mm Hg

0.3 mm Hg

PO2

PCO2

104 mm Hg

40 mm Hg

Pulmonaryarteries

Alveoli

PO2

PCO2

40 mm Hg

45 mm Hg

Blood leavingtissues and

entering lungs:

Blood leavinglungs and

entering tissuecapillaries:PO2

PCO2

100 mm Hg

40 mm Hg

Heart

Systemicveins

Systemicarteries

Internal

respiration

O2 CO2

CO2 O2 O2 CO2

O2 CO2

O2 CO2 O2 CO2

CO2 O2

Tissues:

PO2 less than 40 mm Hg

greater than 45 mm HgPCO2

Oxygen Transport

• Association of oxygen and hemoglobin• Each Hb molecule is composed of four polypeptide

chains, each with a iron-containing heme group• So each Hb can transport four oxygen molecules

• Oxyhemoglobin (HbO2): hemoglobin-O2

combination

• Reduced hemoglobin (deoxyhemoglobin) (HHb): hemoglobin that has released O2

The oxygen-hemoglobin dissociation curve will

help you understand how the properties of

hemoglobin (Hb) affect oxygen binding in the

lungs and oxygen release in the tissues. In the lungs, where PO

2is high

(100 mm Hg), Hb is almostfully saturated (98%) with O2. This axis tells you how much

O2 is bound to Hb. At 100%,each Hb molecule has 4 boundoxygen molecules.

If more O2 is present,more O2 is bound.Howev er, because ofHb’s properties (O2

binding strengthchanges with saturation),this is an S-shaped curve.

This axis tells you the relativeamount (partial pressure) ofO2 dissolv ed in the fluidsurrounding the Hb. In the tissues of other organs,

where PO2 is low (40 mm Hg), Hbis less saturated (75%) with O2.

Hemoglobin

Oxygen

100

80

60

40

20

0 0 20 40 60 80 100

PO2

(mm Hg)

Pe

rce

nt

O2sa

tura

tio

n o

f h

em

oglo

bin

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Oxygen Transport

Influence of other factors on hemoglobin saturation

• 2,3-bisphosphoglycerate (BPG) is produced by RBCs during glycolysis• BPG levels rise when oxygen levels are low

• Increasing BPG binding to Hb: release more O2

• As tissues metabolize glucose, they use O2, causing:• Increases in PCO2

and H+ in capillary blood

• Declining blood pH (acidosis) and increasing Pco2 cause Hb-O2 bond to weaken

• Referred to as Bohr effect

• O2 unloading occurs where needed most

• Heat production in active tissue directly and indirectly decreases Hbaffinity for O2

• Allows increased O2 unloading to active tissues

Changing Delivery of Oxygen by Hemoglobin

• At rest, hemoglobin carries more oxygen than it actually delivers to tissues• Only 23% of what is carried is delivered

• Tissue Po2 determines % liberated

• Hemoglobin saturation (all hemes carrying oxygen) changes with changing conditions• temperature and pH-related conformational shift in

hemoglobin, ↑BPG reduces its capacity to carry

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100

80

60

40

20

0

10°C

20°C38°C

43°C

Normal bodytemperature

Pe

rce

nt

O2

sa

tura

tio

n o

f h

em

og

lob

in

20 40 60 80 100

PO2(mm Hg)

100

80

60

40

20

0

Normal arterialcarbon dioxide(PCO2

40 mm Hg)

or H (pH 7.4)

20 40 60 80 100

PO2(mm Hg)

Pe

rce

nt

O2

sa

tura

tio

n o

f h

em

og

lob

in

Increased carbon dioxide(PCO2

80 mm Hg)or H (pH 7.2)

Decreased carbon dioxide(PCO2

20 mm Hg) or H (pH 7.6)

Carbon Dioxide Transport

• Occurs primarily in RBCs, where enzyme carbonicanhydrase reversibly and rapidly catalyzes this reaction

• In systemic capillaries, after HCO3– is created, it quickly

diffuses from RBCs into plasma• Outrush of HCO3

– from RBCs is balanced as Cl– moves into RBCs from plasma • Referred to as chloride shift

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Carbon Dioxide Transport

Encouraging CO2 exchange at tissues and at lungs

• Haldane effect - amount of CO2 transported is affected by PO2• The lower the PO2

and Hb O2 saturation, the more CO2 Hbcan carry

• Unsaturated Hb buffers H+ and forms carbaminohemoglobin more easily

• Bohr effect - at tissues, as more CO2 enters blood, more oxygen dissociates from hemoglobin • As HbO2 releases O2, it more readily forms

carbaminohemoglobin

Transport and Exchange of CO2 and O2 at Tissues

Oxygen release and carbon dioxide pickup at the tissues

Tissue cell Interstitial fluid

CO2

CO2

CO2

CO2

CO2

CO2 (about 20%)

CO2

O2

O2

CO2 (dissolved in plasma 7-10%)

CO2 H2O H2CO3 HCO3 H

Slow

Fast

Cl

Cl

HCO3

HCO3 H H2CO3CO2 H2O

CO2 Hb HbCO2

HbO2 O2 HbRed blood cell

Carbonic

anhydrase

(Carbamino-

hemoglobin)

HHb

Chlorideshift(in) viatransportprotein

Binds toplasmaproteins

O2 (dissolved in plasma) Blood plasma

Partially saturated, fully saturatedHb Affinity for O2 varies with the extent of oxygen saturationRate of Hb binding/releasing oxygen dependent on PO2, temperature, blood pH, PCO2, and BPG (2,3 bisphosphoglycerate)

oxyhemoglobin

deoxyhemoglobin

As bicarbonate ion 70%

Transport and exchange of CO2

and O2 at lungsCO2

CO2

CO2

CO2

Alveolus

O2

O2

Fused basement membranes

CO2 (dissolved in plasma)

CO2 H2O H2CO3

Slow

Cl

HCO3

Chlorideshift(out) viatransportprotein

Blood plasmaO2 (dissolved in plasma)

Cl

HCO3 H H2CO3CO2 H2O

Carbonicanhydrase

Fast

CO2 Hb HbCO2(Carbamino-hemoglobin)

HbO2 H O2 HHbRed blood cell

HCO3 H

Oxygen pickup and carbon dioxide release in the lungs

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Respiratory centers in the brain stem Pons

Medulla

Pons

Medulla

Intercostal

nerves

External intercostalmuscles

Diaphragm

Dorsal respiratory group (DRG)

integrates peripheral sensory

input and modifies the rhythmsgenerated by the VRG.

Phrenic nerve (from C3, C4, C5) innervates the diaphragm.

Ventral respiratory group (VRG)

contains rhythm generators

whose output drives respiration.

Pontine respiratory centers

interact with the medullary

respiratory centers to smooththe respiratory pattern.

Changes in PCO

2regulate ventilation by a negative feedback mechanism

Arterial PCO2

PCO2decreases pH

in brain extracellular

fluid (ECF)

Central chemoreceptorsin brain stem respond toH in brain ECF (mediate70% of the CO2 response)

Peripheral chemoreceptorsin carotid and aortic bodies

(mediate 30% of the CO2

response)

Afferent impulses

Efferent impulses

Medullary

respiratory centers

Respiratory muscle

Ventilation(more CO2 exhaled)

Arterial PCO2and pH

return to normal

Initial stimulus

Physiological response

Result

Neural and chemical influences on brain stem respiratory centers

Higher brain centers(cerebral cortex—voluntarycontrol over breathing)

Respiratory centers(medulla and pons)

Stretch receptorsin lungs

Centralchemoreceptors

Peripheralchemoreceptors

Other receptors (e.g., pain)and emotional stimuli actingthrough the hypothalamus

Irritantreceptors

Receptors inmuscles and joints

O2,CO2,H

CO2,H

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Responding to Changing Conditions

• What causes change?

• Responses:• Reserve capacity built in

• In volume – structure of conducting passages, muscular involvement, lung involvement

• Dilation

• Recruitment

• In blood flow – adjustment in heart rate and lung involvement

• In hemoglobin – changes in affinity for O2

• In respiratory rate – stimulation from the brain

Respiratory Volumes And Capacities

6000

5000

4000

3000

2000

1000

0

Mil

lili

ters

(m

l)

Inspiratoryreserve volume

3100 ml

Tidal volume 500 ml

Expiratoryreserve volume

1200 ml

Residual volume1200 ml

Functionalresidualcapacity2400 ml

Inspiratorycapacity3600 ml Vital

capacity4800 ml

Total lungcapacity6000 ml

Spirographic record for a male

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Respiratory Volumes And Capacities

Respiratory

volumes

Respiratory

capacities

Summary of respiratory volumes and capacities for males and females

MeasurementAdult male

average value

Adult female

average value Description

Tidal volume (TV)

Inspiratory reservevolume (IRV)

Expiratory reservevolume (ERV)

Residual volume (RV)

Total lung capacity (TLC)

Vital capacity (VC)

Inspiratory capacity (IC)

Functional residualcapacity (FRC)

500 ml 500 ml

3100 ml 1900 ml

1200 ml 700 ml

1200 ml 1100 ml

6000 ml 4200 ml

4800 ml 3100 ml

3600 ml 2400 ml

2400 ml 1800 ml

Amount of air inhaled or exhaled with each breath under restingconditions

Amount of air that can be forcefully inhaled after a normal tidalvolume inspiration

Amount of air that can be forcefully exhaled after a normal tidalvolume expiration

Amount of air remaining in the lungs after a forced expiration

Maximum amount of air contained in lungs after a maximuminspiratory effort: TLC = TV IRV ERV RV

Maximum amount of air that can be expired after a maximuminspiratory effort: VC = TV IRV ERV

Maximum amount of air that can be inspired after a normal tidalvolume expiration: IC = TV IRV

Volume of air remaining in the lungs after a normal tidal volumeexpiration: FRC = ERV RV