The Respiratory System at a Glance

Jeremy P. T. Ward, Jane Ward, Richard M. Leach

• Publisher: Wiley-Blackwell
• Year: 2015
• ISBN:
  9781118761052
• Edition: 4
• Topic: Médecine
• Subtopic: Médecine pulmonaire et thoracique

The Respiratory System at a Glance has been thoroughly updated in line with current practice guidelines and new techniques to provide a highly illustrated and comprehensive guide to normal lung structure and function, as well as associated pathophysiology. Each topic has been fully revised and is accompanied by clear diagrams to encapsulate essential knowledge. Reflecting changes to the content, teaching and assessment methods used in medical education, this new edition now includes more information on acid base and its clinical ramifications, further detail on defence mechanisms and immunology, and also features online access to clinical cases and flashcards. The Respiratory System at a Glance:
•Integrates basic and clinical science – ideal for integrated and systems-based courses
•Includes both the pathophysiology and clinical aspects of the respiratory system
•Is fully revised and updated to reflect current practice guidelines and new therapies
•Provides online clinical cases, brand new flashcards, and MCQs
• Includes a companion website at www.ataglanceseries.com/respiratory featuring interactive multiple choice questions and digital flashcards

Part 1
Structure and function

Chapters

1. 1 Structure of the respiratory system: lungs, airways and dead space
2. 2 The thoracic cage and respiratory muscles
3. 3 Pressures and volumes during normal breathing
4. 4 Gas laws
5. 5 Diffusion
6. 6 Lung mechanics: elastic forces
7. 7 Lung mechanics: airway resistance
8. 8 Carriage of oxygen
9. 9 Carriage of carbon dioxide
10. 10 Acid–base balance
11. 11 Acid–base disorders
12. 12 Control of breathing I: chemical mechanisms
13. 13 Control of breathing II: neural mechanisms
14. 14 Pulmonary circulation and anatomical right-to-left shunts
15. 15 Ventilation–perfusion mismatching
16. 16 Exercise, altitude and diving
17. 17 Development of the respiratory system and birth
18. 18 Complications of development and congenital disease
19. 19 Lung defence mechanisms
20. 20 Immunology of the lung

1
Structure of the respiratory system: lungs, airways and dead space

Lungs

The respiratory system consists of a pair of lungs within the thoracic cage (Chapter 2). Its main function is gas exchange, but other roles include speech, filtration of microthrombi arriving from systemic veins and metabolic activities such as conversion of angiotensin I to angiotensin II and removal or deactivation of serotonin, bradykinin, norepinephrine, acetylcholine and drugs such as propranolol and chlorpromazine. The right lung is divided by transverse and oblique fissures into three lobes: upper, middle and lower. The left lung has an oblique fissure and two lobes (Fig. 1a). Vessels, nerves and lymphatics enter the lungs on their medial surfaces at the lung root or hilum. Each lobe is divided into a number of wedge-shaped bronchopulmonary segments with their apices at the hilum and bases at the lung surface. Each bronchopulmonary segment is supplied by its own segmental bronchus, artery and vein and can be removed surgically with little bleeding or air leakage from the remaining lung.

Figure 1

The pulmonary nerve plexus lies behind each hilum, receiving fibres from both vagi and the second to fourth thoracic ganglia of the sympathetic trunk. Each vagus contains sensory afferents from lungs and airways, parasympathetic bronchoconstrictor and secretomotor efferents, and non-adrenergic, non-cholinergic (NANC). Sympathetic noradrenergic fibres supplying airway smooth muscle are sparse in humans, and the β₂-adrenergic receptors are stimulated by circulating catecholamines from the adrenal glands (Chapter 7).

Each lung is lined by a thin membrane, the visceral pleura, which is continuous with the parietal pleura, lining the chest wall, diaphragm, pericardium and mediastinum. The space between the parietal and visceral layers is tiny in health and lubricated with pleural fluid. The right and left pleural cavities are separate and each extends as the costodiaphragmatic recess below the lungs even during full inspiration. The parietal pleura is segmentally innervated by intercostal nerves and by the phrenic nerve, and so pain from pleural inflammation (pleurisy) is often referred to the chest wall or shoulder tip. The visceral pleura lacks sensory innervation.

Lymph channels are absent in alveolar walls, but accompany small blood vessels conveying lymph towards the hilar bronchopulmonary nodes and from there to tracheobronchial nodes at the tracheal bifurcation. Some lymph from the lower lobe drains to the posterior mediastinal nodes.

The upper respiratory tract consists of the nose, pharynx and larynx. The lower respiratory tract (Fig. 1b) starts with the trachea at the lower border of the cricoid cartilage, level with the sixth cervical vertebra (C6). It bifurcates into right and left main bronchi at the level of the sternal angle and T4/5 (lower when upright and in inspiration). The right main bronchus is wider, shorter and more vertical than the left, so inhaled foreign bodies enter it more easily.

Airways

The airways divide repeatedly, with each successive generation approximately doubling in number. The trachea and main bronchi have U-shaped cartilage, linked posteriorly by smooth muscle. Lobar bronchi supply the three right and two left lung lobes and divide to give segmental bronchi (generations 3 and 4). The total cross-sectional area of each generation is minimum here, after which it rises rapidly, as increased numbers more than make up for their reduced size. Generations 5–11 are small bronchi, the smallest being 1 mm in diameter. The lobar, segmental and small bronchi are supported by irregular plates of cartilage, with bronchial smooth muscle forming helical bands. Bronchioles start at about generation 12 and from this point onwards cartilage is absent. These airways are embedded in lung tissue, which holds them open like tent guy ropes. The terminal bronchioles (generation 16) lead to respiratory bronchioles, the first generation to have alveoli (Chapter 5) in their walls. These lead to alveolar...