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Showing posts with label bronchiole. Show all posts
Showing posts with label bronchiole. Show all posts

Monday, January 5, 2015

Windpipe - Trachea- lungs-

THE WINDPIPE

The windpipe, or trachea, is a tube about four and a half inches long and one inch in diameter. It extends from the bottom of the larynx through the neck and into the chest cavity. At its lower end it divides into two tubes, the right and left bronchi.

The bronchi divide and subdivide many times into smaller branches that penetrate deep into the lungs. The esophagus, which carries food to the stomach, is immediately behind the trachea. Rings of cartilage hold the trachea and bronchi open between breaths. 

The windpipe wall is lined with mucous membrane, and there are many hairslike cilia fanning upward toward the throat, moving dust particles that have been caught in the sticky membrane, thus preventing them from reaching the lungs. Respiratory infections such as colds and sore throats may sometimes extend down into the trachea and bronchi; they are then called tracheitis and bronchitis.

Inflammation of the walls of these passages causes harsh breathing and deep cough.

THE LUNGS 

The two human lungs weigh about two and a half pounds. They have an area forty to fifty times greater than the total surface area of the body's skin-equivalent, some investigators have noted, to the area of a tennis court. Within a lung, the bronchi divide and subdivide, becoming smaller and smaller, until the branches reach a very fine size at which they are called bronchioles. 

Each bronchiole ends in a microscopic air sac, called an alveolus. It has been estimated that human lungs contain more than 750 million alveoli. Filled with air, these tiny sacs give the lungs their characteristic appearance of large sponges.


 A vast network of capillaries penetrates the lungs. Tiny capillaries contact each alveolus. Air in an alveolus is separated from the blood by two thin membranes-the wall of the alveolus and the equally thin wall of a capillary. These thin walls permit ready exchange of gases between blood and air. The lungs ate covered by a double membrane. One, the pleural membrane, lies over the lungs; the other lines the chest cavity. Separating the two is a thin layer of fluid which, during breathing, prevents the two membranes from rubbing against each other. 

Inflammation of the pleura can cause roughness and irritation, the condition called pleurisy. When it is present, the physician, with an ear against the chest, can hear the membranes rubbing each other with each breathing motion.