II. Reading

Read and translate the following text. Get ready to speak about the struc­ture of the human respiratory system.

THE RESPIRATORY SYSTEM

The respiratory system comprises of the nose, mouth, throat, larynx, trachea, bronchi and lungs. The function of the respiratory system is to facilitate gaseous exchange to take place in the lungs and tissue cells of the body.

Oxygen is required by cells in the body to allow various metabolic reactions to take place and to pro­duce energy and is therefore essen­tial to life.

The respiratory system may be defined as the organs and tis­sues through which air is passed into and out of the body to allow the necessary gaseous exchanges to take place.

External respiration is the means by which oxygen from the air passes into the bloodstream for transportation to the tissue cells and carbon dioxide is collected and transferred back to the lungs and expelled from the body.

Internal respiration involves the vital chemical activities that take place in every living cell requiring oxygen and glycogen to combine and release energy, water and carbon dioxide.

Air enters the body through the nose, is warmed, filtered, and passed through the nasal cavity. Air passes the pharynx (which has the epiglottis that prevents food from entering the trachea).The upper part of the trachea contains the larynx (voice box). The vocal cords are two bands of tissue that extend across the opening of the larynx. After passing the larynx, the air moves through the trachea into the bronchi that carry air in and out of the lungs. Bronchi are reinforced to prevent their col­lapse and are lined with ciliated epithelium and mucus-producing cells. Bronchi branch into smaller and smaller tubes known as bronchioles. Bronchioles terminate in grape-like sac clusters known as alveoli. Alveoli are surrounded by a network of thin-walled capillaries. The thin walls of alveoli allow for the exchange of gases between them and the capillaries. The lungs are large, lobed, paired organs in the chest (also known as the thoracic cavity). Though similar in appearance, they are not identical. Both are divided into lobes, with three lobes on the right and two on the left. Thin sheets of epithelium (pleura) separate the inside of the chest cavity from the outer surface of the lungs. The bottom of the thoracic cavity is formed by the diaphragm. The diaphragm is a huge muscle that rests horizontally across the base of the rib cage and helps in the process of breathing. Ventilation is the mecha­nics of breathing in and out.

During inspiration (inhaling):

> the external intercostal muscles contract, lifting the ribs up and out;

> the diaphragm contracts, drawing it down. During expiration (exhaling):

> these processes are reversed;

> the natural elasticity of the lungs returns them to their normal volume.

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