The respiratory system

Unit 7 THE RESPIRATORY SYSTEM

Key words: breathing, internal respiration, external respiration, oxygen, carbon dioxide, the upper

respiratory system, the lower respiratory system, lungs, bronchi, bronchioles, alveoli, larynx, acute

bronchitis, chronic bronchitis, acute and chronic asthma, pulmonary fibrosis, breathing exercises,

pneumonia, tuberculosis, lung carcinoma.

The term respiration refers to three separate but related functions:

1. ventilation (breathing)

2. gas exchange, which occurs between the air and blood in the lungs and between the blood and

other tissues of the body, and

3. oxygen utilization by the tissues in the energy-liberating reactions of cell respiration.

Ventilation and the exchange of gases (oxygen and carbon dioxide) between the air and blood are

called external respiration. Gas exchange between the blood and other tissues and oxygen utilization by the tissues are known as internal respiration.

Ventilation is a mechanical process that moves air into and out of the lungs.

The respiratory system is formed by the nasal cavity, pharynx, larynx, trachea, the bronchi,

bronchioles and alveoli within the lungs. The structures of the upper respiratory system include the nose, pharynx and associated structures. The structures of the lower respiratory system include the larynx, trachea, bronchial tree, alveoli, and the lungs.

The nose is the primary passageway for air entering. The pharynx is a common passageway for the

respiratory and digestive systems. It receives air from the nasal cavity, and air, food and fluid from the oral cavity. The nasal cavity is divided into right and left halves by a nasal septum.

The pharynx is a passageway that connects the nasal and oral cavities to the larynx.

The larynx contains the vocal cords, which are responsible for sound production. The vocal cords

do not vibrate when whispering.

The trachea, commonly called the windpipe, is a passageway, approximately 12 cm long and 2.5

cm in diameter, connecting the larynx to the primary bronchi. The cartilages of the trachea ensure that the airway will always remain open.

Air from the trachea passes through a bronchial tree to alveoli, where gas exchange occurs. The

alveoli are the functional units of the respiratory system and account for most of the mass of the lungs.

The trachea splits to form a right and left primary bronchus. The bronchus divides deeper in the

lungs to form secondary bronchi and tertiary bronchi. The bronchial tree continues to branch into even smaller tubules called bronchioles. At the end of each bronchiole there are microscopic alveoli, or air sacs.

The lungs are paired organs situated within the thoracic cavity. Their surfaces are bordered by the

ribs to the front and back. The right lung is divided into three lobes and the left one into two lobes.

As we breathe, most of the work is done by diaphragm, a sheet of muscle and fibrous tissue that

forms a complete wall between the chest and the abdomen. The ribs provide the upper part of the cage that encloses the heart and lungs and the diaphragm forms the bottom. The muscular fibres of the diaphragm contract when we breathe in. Like any other muscle, the diaphragm receives instructions to contract or relax from the nervous system.