The very thin space between the layers is called the pleural cavity. A liquid, called pleural fluid, lubricates the pleural cavity so that the two layers of pleural tissue can slide against each other. Author: Healthwise Staff. Medical Review: E. This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information.
Your use of this information means that you agree to the Terms of Use. This produces a negative pressure relative to atmospheric pressure inside the intrapleural space of about 0. During inspiration this pressure becomes increasingly negative.
Pleurisy is an inflammation of the pleural membrane, which causes pain when the membranes rub together. Pleural effusion occurs when excess pleural fluid is formed through Law and Watson, :. If the pleural layers are ruptured, for example by a spontaneous rupture of the membrane or by a stab wound, air is sucked into the intrapleural space creating a real air-containing space between the lungs and chest wall - a pneumothorax. This abolishes the negative intrapleural pressure and the lung in the affected area will collapse.
Gas exchange will be seriously impaired because movement of the chest wall will no longer expand the lung. Protecting the delicate gas exchange surfaces in the lung is essential for health and the respiratory system has a number of ways of filtering incoming air:. This not only waterproofs the inside of the respiratory tract and acts as a protective barrier against irritants but also traps bacteria and foreign particles that come into contact with it. Over ml of mucus is produced each day Thibodeau and Patton, and forms a continuous sheet or mucus blanket that covers the tubes of the tract.
The mucus is moved towards the pharynx on small hair-like structures called cilia. Unpleasant stimuli such as dust and debris, noxious vapours including cigarette smoke and allergens or pathogens generally cause a rapid increase in mucus production - a good example is the common cold.
They beat , times a minute, sweeping the mucus, and any trapped particles in it, towards the throat where it is swallowed and destroyed by stomach juices. From the nose, mucus is moved backwards towards the throat but from the rest of the tract it is moved upwards - a system called the mucus escalator.
Many bacteria are trapped in the mucus and are removed in this way. Cigarette smoke causes excess mucus production and paralyses the cilia and allows mucus to accumulate so that smokers have to cough to clear the secretions. A series of short inspirations is followed by an explosive expiration, through the mouth, the nose or both.
This explosive force carries droplets for long distances and is a common means of spreading disease. Receptors in the mucosal lining are activated and cause stimulation of the respiratory control centre in the medulla oblongata of the brain. It descends from the larynx to the superior border of T5, where it bifurcates into the right and left primary bronchi and enters the hilum of each lung. Each primary bronchi on entering the lung, divides into smaller secondary bronchi, one to each lobe of the lung.
Within the substance of the lung the secondary bronchi give rise to the tertiary bronchi. The segment of tissue each tertiary bronchi supplies is called a bronchopulmonary segment.
Each bronchopulmonary segment contains many small components called lobules. A lymphatic vessel. An arteriole. A venule. A branch from a terminal bronchiole. The terminal brochioles continue to branch into respiratory bronchioles.
They in turn branch into many alveolar ducts
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