Ross & Wilson Anatomy and Physiology in Health and Illness (107 page)

Position
240

Structure
240

Functions
241

Lungs
242

Position and gross structure
242

Pleura and pleural cavity
243

Interior of the lungs
244

Bronchi and bronchioles
244

Structure
244

Functions
245

Respiratory bronchioles and alveoli
245

Structure
245

Functions
246

Respiration
246

Breathing
247

Exchange of gases
250

Control of respiration
252

Disorders of the upper respiratory tract
254

Infectious and inflammatory disorders
254

Tumours
255

Obstructive lung disorders
255

Bronchitis
255

Emphysema
256

Asthma
256

Bronchiectasis
257

Cystic fibrosis (mucoviscidosis)
258

Restrictive disorders
258

Pneumoconioses
258

Chemically induced lung diseases
259

Lung infections
260

Pneumonia
260

Lung abscess
261

Tuberculosis (TB)
261

Lung tumours
262

Bronchial carcinoma
262

Pleural mesothelioma
262

Lung collapse
262

ANIMATIONS

10.1
Air distribution through the upper respiratory tract
234

10.2
Air distribution through the lower respiratory tract
234

10.3
Respiratory mucosa
235

10.4
Bronchi and bronchioles
244

10.5
Alveoli
245

10.6
Respiratory membrane
245

10.7
Role of the diaphragm in breathing
247

10.8
Pulmonary ventilation
248

10.9
External repiration
250

10.10
Internal respiration
251

10.11
Summary of external and internal respiration
251

This chapter describes the structure and functions of the respiratory system. Some common respiratory disorders are described in the illnesses section at the end of the chapter.

The cells of the body need energy for all their metabolic activities. Most of this energy is derived from chemical reactions, which can only take place in the presence of oxygen (O
₂
). The main waste product of these reactions is carbon dioxide (CO
₂
). The respiratory system provides the route by which the supply of oxygen present in the atmospheric air enters the body, and it provides the route of excretion for carbon dioxide.

The condition of the atmospheric air entering the body varies considerably according to the external environment, e.g. it may be dry, cold and contain dust particles or it may be moist and hot. As the air breathed in moves through the air passages to reach the lungs, it is warmed or cooled to body temperature, moistened to become saturated with water vapour and ‘cleaned’ as particles of dust stick to the mucus which coats the lining membrane. Blood provides the transport system for O
₂
and CO
₂
between the lungs and the cells of the body. Exchange of gases between the blood and the lungs is called
external respiration
and that between the blood and the cells
internal respiration
. The organs of the respiratory system are:

•
nose

•
pharynx

•
larynx

•
trachea

•
two bronchi (one bronchus to each lung)

•
bronchioles and smaller air passages

•
two lungs and their coverings, the pleura

•
muscles of breathing – the intercostal muscles and the diaphragm.

A general view of the organs of the respiratory system is given in
Figure 10.1.

Figure 10.1 
Structures associated with the respiratory system.

Nose and nasal cavity

Learning outcomes

After studying this section, you should be able to:

describe the location of the nasal cavities

relate the structure of the nasal cavities to their function in respiration

outline the physiology of smell.

Position and structure

The nasal cavity is the main route of air entry, and consists of a large irregular cavity divided into two equal passages by a
septum
. The posterior bony part of the septum is formed by the perpendicular plate of the ethmoid bone and the vomer. Anteriorly, it consists of hyaline cartilage (
Fig. 10.2
).