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医学专业英语 Chapter 5 Respiratory System教案资料
时间:2020-05-26 下载该word文档
精品文档Chapter 5 Respiratory System In this passage you will learn: ● The organs of the respiratory system ● The structure and function of these organs ● The mechanism of breathing ●
The gas transport and cleaning system All living animals must take in oxygen and get rid of carbon dioxide. In the vertebrates—— animals with backbones —— that get their oxygen from the air, both tasks are performed by special gas-exchange organs called lungs. The lungs provide a place where oxygen can reach the blood and carbon dioxide can be removed from it. They are equipped with tubes and a bellows system for drawing in air from the outside, while the pulmonary veins and arteries circulate blood through from inside. The lungs also have a cleaning system that traps, ejects, or destroys irritants and other harmful substances that travel in with the air. In the simpler cold-blooded amphibians and reptiles, the lungs are two balloon-like sacs. In active animals that require large amounts of oxygen, especially the warm-blooded birds and mammals , the lungs are a spongy labyrinth of sacs that supply an enormous surface area for the transfer of gases. In the adult human the total lung surface, if flattened out, would be larger than a badminton court, about 100 square yards (83 square meters. Air enters the body through the nose and passes through the nasal cavity, which is lined with a mucous membrane and fine hairs (cilia to help filter out foreign bodies, as well as to warm and moisten the air. Paranasal sinuses are hollow, air-containing spaces within the skull that communicate with the nasal cavity. They, too, have a mucous membrane lining and function to provide the lubricating fluid mucus. as well as to lighten the bones of the skull and help produce sound. After passing through the nasal cavity, the air next reaches the pharynx (throat. There are three divisions of the pharynx. The nasopharynx is the first division, and it is nearest to the nasal cavities. It contains the adenoids, which are masses of lymphatic tissue. The adenoids (also known 精品文档
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as the pharyngeal tonsils are more prominent in children, and if enlarged, they can obstruct air passageways . Below the nasopharynx and closer to the mouth is the second division of the pharynx, the oropharynx. The palatine tonsils, two rounded massed of lymphatic tissue, are located in the oropharynx. The third division of the pharynx is the hypopharynx (also called the laryngopharynx.
It is in the hypopharyngeal region that the pharynx, serving as a common passageway for food from the mouth and air from the nose, divides into two branches, the larynx (voice box and the esophagus. The esophagus leads into the stomach and carries food to be digested. The larynx contains the vocal cords and is surrounded by pieces of cartilage for support. Sounds are produced as air is expelled past the vocal cords, and the cords vibrate. The tension of the vocal cords determines the high or low pitch of the voice. Since food entering from the mouth and air entering from the nose mix in the pharynx, what prevents the passing of food or drink into the larynx and respiratory system after it has been swallowed? Even with a small quantity of solid or liquid matter finding its way into the air passages, breathing could be seriously blocked. A special deterrent to this event is provided for by a flap of cartilage attached to the root of the tongue that acts like a lid over the larynx. This flap of cartilage is called the epiglottis. The epiglottis lies over the entrance to the larynx. In the act of swallowing, when food and liquid move through the throat, the epiglottis closes off the larynx, so that these things cannot enter. On its way to the lungs, air passes from the larynx to the trachea (windpipe, a vertical tube about 412 inches long and 1 inch in diameter. The trachea is kept open by 16-20 C-shaped rings of cartilage separated by fibrous connective tissue that stiffens the front and sides of the tube. In the region of the mediastinum, the trachea divides into two branches called bronchi. Each bronchus leads