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Chapter 23 Respiratory System

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23.1 Functions of the Respiratory System

• Ventilation: Movement of air into and out of lungs

• External respiration: Gas exchange between air in lungs and blood

• Transport of oxygen and carbon dioxide in the blood

• Internal respiration: Gas exchange between the blood and tissues

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Respiratory System Functions 1. Regulation of blood pH: Altered by changing blood CO2 2. Production of chemical mediators: ACE 3. Voice production: Movement of air past vocal folds makes sound

and speech 4. Olfaction: Smell occurs when airborne molecules are drawn into

nasal cavity 5. Protection: Against microorganisms by preventing entry and

removing them from respiratory surfaces.

Fig. 23.10

Sternocleidomastoid

Scalenes

Diaphragm

The diaphragm contracts, increasing the superior–inferior dimension of the thoracic cavity.

Labored breathing: additional muscles contract, causing additional expansion of the thorax.

Abdominal muscles relax.

End of inspiration

End of expiration

Muscles of inspiration

Pectoralis minor

External intercostals

Diaphragm relaxed

Abdominal muscles

Clavicle (cut)

Internal intercostals Muscles

of expiration

Quiet breathing: the external intercostal muscles contract, elevating the ribs and moving the sternum.

(a)

(b)

Muscles of Respiration

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Inspiration and Expiration Inspiration • Diaphragm, external intercostals, pectoralis minor, scalenes • Diaphragm: Central tendon: top of dome • Quiet inspiration: Inferior movement of central tendon and

flattening of dome. Abdominal muscles relax Expiration • Muscles that depress the ribs and sternum: abdominal muscles

and internal intercostals. • Quiet expiration: relaxation of diaphragm and external

intercostals with contraction of abdominal muscles • Labored breathing: all inspiratory muscles are active and

contract more forcefully. Expiration is rapid.

Right lung

Heart

Sternum

Superior view

Left lung

Pleural cavity

Parietal pleura

Fibrous pericardium

Parietal pericardium

Pericardial cavity

Vertebra

Esophagus in posterior mediastinum)

Visceral pleura

Visceral pericardium Anterior mediastinum

Pulmonary trunk

Root of lung at hilum

Right main bronchus Right pulmonary artery Right pulmonary vein

Pleura Pleural cavity • Contains pleural fluid (acts as a lubricant)

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Blood and Lymphatic Supply Two sources of blood to lungs: • Pulmonary artery…… • Pulmonary veins….. • Bronchial arteries….. • Bronchial veins….to the azygous, merges with alveolar

capillaries Two lymphatic supplies • Superficial and deep lymphatic vessels….. • Superficial drain superficial lung tissue and visceral pleura • Deep drain bronchi and associated C.T.

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23.3 Ventilation • What is ventilation?...... • What drives ventilation?....... • What is pressure?....... • Boyle’s Law: P = k/V, where P = gas pressure, V = volume, k =

constant at a given temperature. • Pressure and volume….. • How does the diaphragm alter pressure?

– Muscular contraction….. – Displacement increases thoracic volume…Boyle’s

law?....

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Intra-alveolar Pressure Changes

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Intra-alveolar Pressure Changes

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Inspiration Expiration

Decrease, increasing thoracic volume

1) Decrease (increasing thoracic volume)

2) Increase (increasing ambient air molecules)

Expanding thoracic volume

Increasing, assists with air expulsion

1) Increase (elastic recoil, muscular contraction)

2) Decrease (back to 0)

Decrease….”contracting” thoracic volume

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Compliance • Measure of the ease with which lungs and thorax expand • The greater the compliance, the easier it is for a change in pressure to

cause expansion • A lower-than-normal compliance means the lungs and thorax are

harder to expand…… • Pulmonary fibrosis: deposition of inelastic fibers in lung

(emphysema) Pulmonary edema • Increased resistance to airflow caused by airway obstruction (asthma,

bronchitis, lung cancer) • Deformities of the thoracic wall (kyphosis, scoliosis)

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23.4 Measurement of Lung Function • Spirometry: measures volumes of air that move into and out of

respiratory system. • Tidal volume: amount of air inspired or expired with each

breath. At rest: 500 mL • Inspiratory reserve volume: amount that can be inspired

forcefully after inspiration of the tidal volume (3000 mL at rest)

• Expiratory reserve volume: amount that can be forcefully expired after expiration of the tidal volume (100 mL at rest)

• Residual volume: volume still remaining in respiratory passages and lungs after most forceful expiration (1200 mL)

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Pulmonary Capacities • The sum of two or more pulmonary volumes • Inspiratory capacity: tidal volume plus inspiratory

reserve volume • Functional residual capacity: expiratory reserve

volume plus residual volume • Vital capacity: sum of inspiratory reserve volume, tidal

volume, and expiratory reserve volume • Total lung capacity: sum of inspiratory and expiratory

reserve volumes plus tidal volume and residual volume.

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Minute Ventilation and Alveolar Ventilation • Minute ventilation: total air moved into and out of

respiratory system each minute; tidal volume X respiratory rate

• Respiratory rate (respiratory frequency): number of breaths taken per minute

• Anatomic dead space: formed by nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles

• Physiological dead space: anatomic dead space plus the volume of any alveoli in which gas exchange is less than normal.

• Alveolar ventilation (VA): volume of air available for gas exchange/minute

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23.5 Physical Principles of Gas Exchange Partial pressure • The pressure exerted by each type of gas in a mixture • Dalton’s law: total pressure is the sum of the individual

pressures of each gas. • Ptotal = • Air in the respiratory system adds H2O….mucus lining Diffusion of gases through liquids • Henry’s Law: Concentration of a gas in a liquid is determined

by its partial pressure and its solubility coefficient

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Physical Principles of Gas Exchange FACTORS:

1. Membrane thickness……barrier to gas exchange 2. Diffusion coefficient of gas. CO2 is 20 times more

diffusible than O2 3. Surface area. ....emphysema, lung cancer destroys lung

tissue…..loss of alveoli, decrease in surface area, less diffusion

4. Partial pressure differences. Separate for O2 and CO2…. High to low pressure

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23.6 Oxygen and Carbon Dioxide Transport in the Blood

Oxygen • Moves from alveoli into blood • Oxygen moves from tissue

capillaries into the tissues 2 modes of transport: • Dissolved… • RBC….

Carbon dioxide • Moves from tissues into tissue

capillaries • Moves from pulmonary

capillaries into the alveoli 3 modes of transport: • Dissolved • RBC • Bicarbonate

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Gas Exchange

Inspired air PO2 = 160 mmHg Alveolar air PO2 = 104 mmHg Why the decrease? • Pulmonary veins PO2 = 95 mmHg Why the decrease? •

Expired air

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Dissociation curve What is the “Dissociation curve” • Graph depicting the relative amount of O2 bound to hemoglobin • Not a constant value Depends on: • Location in the cardiovascular system • Amount of dissolved O2 (how much?......)

0

20

20 40 60

% O

2 sa

tura

tion

80 100 105

40

60

80

100

Po2 (mm Hg)

Po2 in tissue at rest

Po2 in lungs

Oxygen released to tissue during exercise: 73%

Oxygen released to tissue at rest: 23%

Dissociation Curve

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Factors affecting the dissociation curve 1) PO2……due to less (or more) dissolved O2 molecules 2) PCO2…..related to decrease in pH 3) pH or [H+]…..Bohr effect 4) Temperature……increased kinetic activity of molecules 5) 2,3 BPG • 2,3 bisphosphoglycerate • produced by RBC & alters O2-Hb affinity

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Shifting the Curve

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Shifting the Curve

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Transport of Carbon Dioxide

• Bicarbonate ions (70%) • Combination with RBC proteins (23%: primarily hemoglobin) • Dissolved in plasma (7%)…..establishes PCO2

• Hemoglobin that has released oxygen binds more readily to carbon dioxide than hemoglobin that has oxygen bound to it (Haldane effect)

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Carbon Dioxide Transport: Internal Respiration Tissue level

CA = carbonic anhydrase

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Carbon Dioxide Transport: External Respiration Lung level

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23.7 Regulation of Ventilation

Medullary respiratory center • Dorsal groups stimulate the

diaphragm • Ventral groups stimulate the

intercostal and abdominal muscles Pontine (pneumotaxic) respiratory

group • Regulates the breathing rhythm

(inspiration and expiration)

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Rhythmic Ventilation Starting inspiration • Medullary respiratory center neurons are continuously active • Input received from receptors that monitor blood gases, temperature. Increasing inspiration • Increased motor neuron activation……increases breathing depth Stopping inspiration • Inhibitory neurons to medullary respiratory centre

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Chemical Control of Ventilation Effect of carbon dioxide: • Increase in rate and depth of respiration • Hypercapnia: greater-than-normal amount of carbon dioxide • Hypocapnia: lower-than-normal amount of carbon dioxide • Chemosensitive area in medulla oblongata is more important for regulation of

PCO2 and pH • Carotid bodies respond rapidly to changes in blood pH because of exercise Effect of oxygen: • Carotid and aortic body chemoreceptors respond to decreased PO2 by increased

stimulation of respiratory center • Hypoxia: decrease in oxygen levels below normal values

Question 1

Which of these structures is a part of the upper respiratory tract?

A. bronchi B. larynx C. lungs D. pharynx E. trachea

Question 2

The structure that separates the nasopharynx from the oropharynx is the

A. hard palate. B. larynx. C. fauces. D. uvula. E. vestibule.

Question 3

The true vocal cords and the opening between them are called the

A. cricoid cartilage. B. fauces. C. glottis. D. thyroid cartilage. E. vestibular folds.

Question 4

At the end of normal inspiration, which of these pressures is the most negative?

A. alveolar B. barometric C. partial D. pleural E. tracheal

Question 5

Most carbon dioxide is transported as __________ in the blood.

A. bicarbonate ions B. carbamino compounds (including

carbaminohemoglobin) C. dissolved in plasma D. carbon monoxide E. carbonic acid

Question 6

Which of these factors increases respiratory rate?

A. increased blood PCO2 B. increased blood pH C. increased blood PO2 D. increased pH of cerebrospinal fluid E. all of these

Question 7 Which of these statements concerning respiration is NOT

true? A. Higher brain centers can modify the activity of the

respiratory center. B. A decrease in pH of the blood increases respiration

rate. C. The Bohr effect allows carbon dioxide to bind more

easily to hemoglobin that has released its oxygen. D. An increase in carbon dioxide in the blood causes pH

to decrease. E. Low oxygen levels in the blood increase respiration

rate.