Chapter 17

Mechanics of Breathing

About this Chapter

• The respiratory system• Gas laws• Ventilation

Respiratory System

Functions• External Respiration• Exchange of gases between the atmosphere

and the blood

• Homeostatic regulation of body pH• Protection from inhaled pathogens and

irritating substances• Vocalization

Respiratory System

Principles of Bulk Flow• Flow from regions of higher to lower pressure• Muscular pump creates pressure gradients• Resistance to flow • Diameter of tubes

Respiratory System

• Overview of external and cellular respiration

Figure 17-1

CO2 O2

Alveoliof lungs

Airways

CO2

CO2

O2

O2

Pulmonarycirculation

CO2O2

Cellularrespiration

ATPNutrients

Cells

Systemiccirculation

CO2 O2

Exchange I:atmosphereto lung(ventilation)

Transport ofgases inthe blood

Exchange III:blood to cells

Exchange II:lung to blood

Respiratory System Components

• Conducting system• Alveoli• Bones and muscle of thorax

Respiratory System

Figure 17-2a

Rightbronchus

Left bronchus

Left lung

Diaphragm

(a) The respiratory system

Upperrespiratory

system

Lowerrespiratory

system

Right lung

TracheaLarynx

Esophagus

Vocal cords

Pharynx

Tongue

Nasal cavity

ANATOMY SUMMARY

THE LUNGS AND THORACIC CAVITY

Muscles Used for Ventilation

Figure 17-2b

Scalenes

Sternocleido-mastoids

Externalintercostals

Muscles ofinspiration

Muscles ofexpiration

Abdominalmuscles

Diaphragm

(b) Muscles used for ventilation

Internalintercostals

The Respiratory System

Figure 17-3

Air-filledballoon

Fluid-filled balloon

Pleuralfluid

Pleuralmembrane

Air spaceof lung

Branching of Airways

Figure 17-2e

Bronchiole

Trachea

Cartilagering

Larynx

Secondarybronchus

Left primarybronchus

(e) Branching of airways

Alveoli

ANATOMY SUMMARY

THE LUNGS AND THORACIC CAVITY

Branching of the Airways

Figure 17-4

Conditioning Air

• Warming air to body temperature• Adding water vapor• Filtering out foreign material

Ciliated Respiratory Epithelium

Figure 17-5

Cilia move mucus to pharynx

Cilia

Goblet cellsecretes mucus.

Nucleus ofcolumnar

epithelial cell

Basementmembrane

Dust particle

Mucus layer trapsinhaled particles.inhaled particles.

Watery saline layerallows cilia topush mucus

toward pharynx.

Ciliated epithelium of the trachea

Alveolar Structure – Note cell types of alveoli

Figure 17-2g

Pulmonary Circulation

• Right ventricle pulmonary trunk lungs pulmonary veins left atrium

• Note oxygenation

Anatomy Review

PLAY Interactive Physiology® Animation: Respiratory System: Anatomy Review

Gas Laws

Table 17-1

Table 17-2

Gas Laws

• Pgas = Patm % of gas in atmosphere

Figure 17-6

Boyle’s Law

• Gases move from areas of high pressure to areas of low pressure

Spirometer

Figure 17-7

Inspiration

Time

Air

Water

Expiration Inspiration Expiration

0.5

0

Volume(L)

Bell

Lung Volumes and Capacities

Figure 17-8

Air Flow

• Flow P/R• Alveolar pressure or intrapleural pressure

can be measured• Single respiratory cycle consists of one

inspiration followed by one expiration

Movement of the Diaphragm

Figure 17-9a

Movement of the Diaphragm

Figure 17-9b

Movement of the Diaphragm

Figure 17-9c

Dimensions of the Thoracic Cavity During Inspiration

Figure 17-10a

Dimensions of the Thoracic Cavity During Inspiration

Figure 17-10b

Pressure Changes During Quiet Breathing

Figure 17-11

Trachea

Bronchi

Lung

Diaphragm

Right pleuralcavity

Left pleuralcavity

+2

+1

0

–1

–2

–3

–4

–5

–6

500

750

250

0 1 2 3 5 6 7 84

A1

B1

C1

A2

A3

A4

B2

B3

Time (sec)

C2

A5

C3

Alveolarpressure(mm Hg)

Intrapleuralpressure(mm Hg)

Volumeof air

moved(mL)

Inspiration Expiration Inspiration Expiration

Subatmospheric Pressure in the Pleural Cavity

Figure 17-12a

Intrapleuralspace

Pleuralmembranes

Diaphragm

P = –3 mm HgIntrapleural pressureis subatmospheric.

Ribs

(a) Normal lung at rest

Elastic recoil of thechest wall tries to pull

the chest wall outward.

Elastic recoil of lungcreates an inward pull.

Subatmospheric Pressure in the Pleural Cavity

• Pneumothorax results in collapsed lung that cannot function normally

Figure 17-12b

P = Patm

Lung collapses tounstretched size

Knife

Intrapleuralspace

(b) Pneumothorax

Pleuralmembranes

If the sealed pleural cavity is openedto the atmosphere, air flows in.

The rib cageexpands slightly.

Air

Compliance and Elastance

• Compliance: ability to stretch• High compliance • Stretches easily

• Low compliance • Requires more force• Restrictive lung diseases • Fibrotic lung diseases• Inadequate surfactant production

• Elastance: returning to its resting volume when stretching force is released

Law of LaPlace

• Surface tension is created by the thin fluid layer between alveolar cells and the air

Figure 17-13

Surfactant

• More concentrated in smaller alveoli• Mixture containing proteins and

phospholipids• Newborn respiratory distress syndrome• Premature babies• Inadequate surfactant concentrations

Air Flow

Table 17-3

Pulmonary Ventilation

PLAY Interactive Physiology® Animation: Respiratory System: Pulmonary Ventilation

Ventilation

• Total pulmonary ventilation is greater than alveolar ventilation because of dead space

• Total pulmonary ventilation = ventilation rate tidal volume

Ventilation

Figure 17-14

1

2

3

4

2

3

4

1

150

150mL

350

150

2700 mL

2200 mL

2200 mL

150mL

2200 mL

150mL

Only 350 mLof fresh air

reaches alveoli

The first exhaledair comes out ofthe dead space.Only 350 mLleaves the alveoli.

Dead space isfilled withfresh air.

The first 150 mLof air into the

alveoli is staleair from thedead space.

RESPIRATORYCYCLE INADULT

Dead space filledwith stale air

Dead space filledwith fresh air

150 mm Hg (fresh air)100 mm Hg (stale air)

End of inspiration

At the end of expiration, thedead space is filled with“stale” air from alveoli.

Inhale 500 mLof fresh air (tidal volume).

KEY

Exhale 500 mL(tidal volume)

Atmosphericair

150

350

PO2=

PO2~~

Ventilation

• Alveolar ventilation = ventilation rate (tidal volume – dead space volume)

Table 17-4

Ventilation

Table 17-5

Ventilation

Table 17-6

Figure 17-15

Ventilation

• As alveolar ventilation increases, alveolar

PO2 increases and PCO2 decreases

Ventilation

Table 17-7

Ventilation

• Local control mechanisms attempt to match ventilation and perfusion

Figure 17-16a

Ventilation

Figure 17-16b

Ventilation

Figure 17-16c

Ventilation

• Auscultation = diagnostic technique• Obstructive lung diseases• Asthma• Emphysema• Chronic bronchitis

Summary

• Respiratory system• Cellular respiration, external respiration,

respiratory system, upper respiratory tract, pharynx, and larynx

• Lower respiratory tract, trachea, bronchi, bronchioles, alveoli, Type I and Type II alveolar cells

• Diaphragm, intercostal muscles, lung, pleural sac, and pleural fluid

• Gas Laws: Dalton’s law and Boyle’s law

Summary

• Ventilation• Tidal volume, vital capacity, residual volume,

and respiratory cycle• Alveolar pressure, active expiration, intrapleural

pressures, compliance, elastance, surfactant, bronchoconstriction, and bronchodilation

• Total pulmonary ventilation, alveolar ventilation, hyperventilation, and hypoventilation