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Structure and Function of the Pulmonary System

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Structures of the Pulmonary System

Airways Pulmonary circulation Chest wall Lungs

Lobes (three on right, two on left) Segments Lobules

Mediastinum

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Structures of the Pulmonary System (cont’d)

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Structures of the Pulmonary System (cont’d)

Conducting airways: Upper airways:

• Nasopharynx• Oropharynx

Larynx• Connects upper and lower airways

Lower airways:• Trachea• Bronchi• Terminal bronchioles

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Structures of the Pulmonary System (cont’d)

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Structures of the Pulmonary System (cont’d)

Gas-exchange airways: Respiratory bronchioles Alveolar ducts Alveoli

• Epithelial cells: Type I alveolar cells

– Alveolar structure Type II alveolar cells

– Surfactant production

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Structures of the Pulmonary System (cont’d)

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Structures of the Pulmonary System (cont’d)

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Pulmonary and Bronchial Circulation

Pulmonary circulation has a lower pressure than the systemic circulation

One-third of pulmonary vessels are filled with blood at any given time

Pulmonary artery divides and enters the lung at the hilus

Each bronchus and bronchiole has an accompanying artery or arteriole

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Pulmonary and Bronchial Circulation (cont’d)

Alveolocapillary membrane Formed by the shared alveolar and capillary

walls Gas exchange occurs across this membrane

Pulmonary veins Each drains several pulmonary capillaries Dispersed randomly throughout the lung Leave the lung at the hila and enter the left

atrium

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Pulmonary and Bronchial Circulation (cont’d)

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Chest Wall and Pleura

Chest wall Skin, ribs, and intercostal muscles Thoracic cavity

Pleura Serous membrane Parietal and visceral layers Pleural space (cavity) Pleural fluid

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Thoracic Cavity

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Function of the Pulmonary System

Ventilate the alveoli Diffuse gases into and out of the blood Perfuse the lungs so the body receives

oxygen

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Function of the Pulmonary System (cont’d)

Ventilation Mechanical movement of gas or air into and

out of the lungs Minute volume

• Ventilatory rate multiplied by the volume of air per breath

Alveolar ventilation

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Ventilation

Respiratory center• Dorsal respiratory

group• Ventral respiratory

group• Pneumotaxic center• Apneustic center

Peripheral chemoreceptors

Lung receptors:• Irritant receptors• Stretch receptors• J receptors

Chemoreceptors:• Central

chemoreceptors• Peripheral

chemoreceptors

Neurochemical control

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Neurochemical Respiratory Control

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Mechanics of Breathing

Major and accessory muscles: Major muscles of inspiration:

• Diaphragm• External intercostals

Accessory muscles of inspiration:• Sternocleidomastoid muscle• Scalene muscles

Accessory muscles of expiration:• Abdominal intercostal muscles• Internal intercostal muscles

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Muscles of Ventilation

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Mechanics of Breathing

Alveolar surface tension and ventilation Function of surfactant

Elastic properties of the lung and chest wall: Elastic recoil Compliance

Airway resistance Work of breathing

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Mechanics of Breathing (cont’d)

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Gas Transport

Four steps Ventilation of the lungs Diffusion of oxygen from the alveoli into the

capillary blood Perfusion of systemic capillaries with

oxygenated blood Diffusion of oxygen from systemic capillaries

into the cells Diffusion of CO2 occurs in reverse order

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Measurement of Gas Pressure

Barometric pressure Partial pressure

Partial pressure of water vapor

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Measurement of Gas Pressure (cont’d)

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Gas Transport

Distribution of ventilation and perfusion Gravity and alveolar pressure Ventilation-perfusion ratio

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Gas Transport (cont’d)

Oxygen transport Diffusion across the alveolocapillary membrane Determinants of arterial oxygenation:

• Hemoglobin binding• Oxygen saturation

Oxyhemoglobin association and dissociation• Oxyhemoglobin dissociation curve• Bohr effect

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Measurement of Gas Pressure

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Gas Transport

Carbon dioxide transport Dissolved in plasma Bicarbonate Carbamino compounds

Haldane effect

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Control of Pulmonary Circulation

Hypoxic pulmonary vasoconstriction Caused by low alveolar paO2

Blood is shunted to other, well-ventilated portions of the lungs

• Provides better ventilation and perfusion matching• If hypoxia affects all segments of the lungs, the

vasoconstriction can result in pulmonary hypertension

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Control of Pulmonary Circulation (cont’d)

Acidemia also causes pulmonary artery constriction

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Tests of Pulmonary Function

Spirometry Diffusion capacity Residual volume Functional reserve capacity (FRC) Total lung capacity Arterial blood gas analysis Chest radiographs

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Aging and the Pulmonary System

Loss of elastic recoil Stiffening of the chest wall Alterations in gas exchange Increases in flow resistance Decreased exercise tolerance

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Aging and the Pulmonary System (cont’d)