Smoking and Lung Cancer

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Lung cancer (fig. 22.26) accounts for more deaths than any other form of cancer. The most important cause of lung cancer is cigarette smoking, distantly followed by air

23emphys = inflamed

Saladin: Anatomy & I 22. The Respiratory System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

870 Part Four Regulation and Maintenance

870 Part Four Regulation and Maintenance

Copd Lung Cancer Photos
Figure 22.26 Effect of Smoking. (a) A healthy adult lung. (b) A smoker's lung with carcinoma.

pollution. Cigarette smoke contains at least 15 carcinogenic compounds. Lung cancer commonly follows or accompanies COPD.

There are three forms of lung cancer, the most common of which is squamous-cell carcinoma. This form begins with the multiplication of basal cells of the bronchial epithelium and transformation of the ciliated pseudostratified columnar epithelium into the stratified squamous type. As the dividing epithelial cells invade the underlying tissues of the bronchial wall, the bronchus develops bleeding lesions. Dense swirled masses of keratin appear in the lung parenchyma and replace functional respiratory tissue. A second form of lung cancer, nearly as common, is adenocarcinoma,24 which originates in

24adeno = gland + carcino = cancer + oma = tumor mucous glands of the lamina propria. The least common (10%-20% of malignancies) but most dangerous form is small-cell (oat-cell) carcinoma, named for clusters of cells that resemble oat grains. This originates in the primary bronchi but invades the mediastinum and metastasizes quickly to other organs.

Over 90% of lung tumors originate in the mucous membranes of the large bronchi. As a tumor invades the bronchial wall and grows around it, it compresses the airway and may cause atelectasis (collapse) of more distal parts of the lung. Growth of the tumor produces a cough, but coughing is such an everyday occurrence among smokers it seldom causes much alarm. Often, the first sign of serious trouble is the coughing up of blood. Lung cancer metastasizes so rapidly that it has usually spread to other organs by the time it is diagnosed. Common sites of

Saladin: Anatomy & I 22. The Respiratory System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Chapter 22 The Respiratory System 871

Table 22.5 Some Disorders of the Respiratory System

Acute rhinitis

The common cold. Caused by many types of viruses that infect the upper respiratory tract. Symptoms include congestion, increased nasal secretion, sneezing, and dry cough. Transmitted especially by contact of contaminated hands with mucous membranes; not transmitted orally. Acute lung inflammation and alveolar injury stemming from trauma, infection, burns, aspiration of vomit, inhalation of noxious gases, drug overdoses, and other causes. Alveolar injury is accompanied by severe pulmonary edema and hemorrhage, followed by fibrosis that progressively destroys lung tissue. Fatal in about 40% of cases under age 60 and in 60% of cases over age 65.

A lower respiratory infection caused by any of several viruses, fungi, or protozoans (most often the bacterium Streptococcus pneumoniae). Causes filling of alveoli with fluid and dead leukocytes and thickening of the respiratory membrane, which interferes with gas exchange and causes hypoxemia. Especially dangerous to infants, the elderly, and people with compromised immune systems, such as AIDS and leukemia patients. Cessation of breathing for 10 seconds or longer during sleep; sometimes occurs hundreds of times per night, often accompanied by restlessness and alternating with snoring. Can result from altered function of CNS respiratory centers, airway obstruction, or both. Over time, may lead to daytime drowsiness, hypoxemia, polycythemia, pulmonary hypertension, congestive heart failure, and cardiac arrhythmia. Most common in obese people and in men.

Tuberculosis (TB) Pulmonary infection with the bacterium Mycobacterium tuberculosis, which invades the lungs by way of air, blood, or lymph.

Stimulates the lung to form fibrous nodules called tubercles around the bacteria. Progressive fibrosis compromises the elastic recoil and ventilation of the lungs. Especially common among impoverished and homeless people and becoming increasingly common among people with AIDS.

Disorders described elsewhere

Adult respiratory distress syndrome


Sleep apnea

Apnea 857 Asthma 828 Atelectasis 853

Carbon monoxide poisoning 864 Chronic bronchitis 869 Cor pulmonale 740

Decompression sickness 872 Dyspnea 857 Emphysema 869 Hypoxia 869 Lung cancer 869 Ondine's curse 859

Pleurisy 849 Pneumothorax 853 Pulmonary edema 861 Respiratory acidosis 868 Respiratory alkalosis 868 Respiratory distress syndrome 855

metastasis are the pericardium, heart, bones, liver, lymph nodes, and brain. The chance of recovery is poor, with only 7% of patients surviving for 5 years after diagnosis.

Some infectious diseases and other disorders of the respiratory system are briefly described in table 22.5. The effects of aging on the respiratory system are described on p. 1111.

Before You Go On

Answer the following questions to test your understanding of the preceding section:

22. Describe the four classes of hypoxia.

23. Name and compare two COPDs and describe some pathological effects that they have in common.

24. In what lung tissue does lung cancer originate? How does it kill?

Saladin: Anatomy & I 22. The Respiratory System I Text I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

872 Part Four Regulation and Maintenance

Insight 22.4 Clinical Application

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