The respiratory system

The rate of breathing is controlled by the respiratory centre of the brain, the medulla oblongata, and is regulated according to the levels of carbon dioxide in the blood, rather than the amount of oxygen present. The brain will respond to an increased production of carbon dioxide, such as when the body undergoes physical exercise, and adjust the breathing rate accordingly.

We breathe an average of 15 times per minute during quiet breathing and more quickly

during exertion or in the course of various illnesses. A normal person exchanges approximately 6 litres of air in each minute of quiet breathing.

Cessation of breathing during sleep, or sleep apnoea, is caused by a variety of disease processes.

Victims of sudden infant death syndrome as a tragic form of sleep apnoea are apparently healthy twoto five-month-old babies who die in their sleep without apparent reason. These deaths seem to be caused, for instance, by failure of the respiratory control mechanism in the brain stem.

COMMON RESPIRATORY DISORDERS

A cough is the most common symptom of respiratory disorders. The common cold is the most

widespread of all respiratory diseases. Colds occur repeatedly because acquired immunity to one virus does not protect against other viruses that cause colds. Cold viruses cause acute inflammation of the respiratory mucosa, resulting in a flow of mucus, a fever, and often a headache.

Influenza is a viral disease that can become epidemic, but fortunately vaccines are available.

Acute bronchitis is an inflammation of the trachea and bronchial tubes. Acute bronchitis results

from living in a dusty, damp and foggy atmosphere and smoking. It is characterized by a persistent dry cough that may last several weeks.

Chronic bronchitis results from recurrent attacks of acute bronchitis or prolonged exposure to

chemical irritation from cigarettes, exposure to smoke and dust. It is incurable, but early treatment

prevents progression and lung damage. Chronic bronchitis is a disorder characterized by increased mucus secretion in the bronchi.

Asthma is a chronic disorder manifested by attacks of dyspnoea in which the air in the alveoli

becomes trapped and entrance of fresh air is prevented. The main reason of asthma is allergy, such as hay fever, hypersensitivity to certain drugs or food or substances inhaled.

In a condition of pulmonary fibrosis the normal structure of the lungs is altered by the accumulation of fibrous connective tissue proteins. The type of fibrosis anthracosis, or black lung, is produced by the inhalation of carbon particles from coal dust.

Pneumonia is an acute infection and inflammation of lung tissue. It is usually caused by bacteria,

most commonly the pneumococcus bacterium. Bacterial disease has a sudden onset of symptoms: fever, chills, chest pain, increased pulse and respiration and painful coughing.

Tuberculosis (TB) is an inflammatory disease of the lungs. Tuberculosis softens lung tissues and

leads to ulceration of the tissues.

The incidence of lung carcinoma is greater in males than females. It often results from a constant irritation by inhaled cigarette smoke. For people who regularly smoke a pack of cigarettes a day, the risk in developing carcinoma is 20 times greater than for people who have never smoked.