The human respiratory system consists of a complex set of organs and tissues that capture oxygen from the environment and transport the oxygen into the lungs. The organs and tissues that comprise the human respiratory system include the nose and pharynx, the trachea, and the lungs. Nose and pharynx
The respiratory system of humans begins with the nose, where air is conditioned by warming and moistening. Bone partitions separate the nasal cavity into chambers, where air swirls about in currents. Hairs and hairlike cilia trap dust particles and purify the air. The nasal chambers open into a cavity at the rear of the mouth called the pharynx(throat). From the pharynx, two tubes called Eustachian tubes open to the middle ear to equalize air pressure there. The pharynx also contains tonsils and adenoids, which are pockets of lymphatic tissue used to trap and filter microorganisms. Trachea
After passing through the pharynx, air passes into the windpipe, or trachea. The trachea has a framework of smooth muscle with about 16 to 20 open rings of cartilage shaped like a C. These rings give rigidity to the trachea and ensure that it remains open. The opening to the trachea is a slitlike structure called the glottis. A thin flap of tissue called the epiglottis folds over the opening during swallowing and prevents food from entering the trachea. At the upper end of the trachea, several folds of cartilage form the larynx, or voicebox. In the larynx, flaplike pairs of tissues calledvocal cords vibrate when a person exhales and produce sounds. At its lower end, the trachea branches into two large bronchi (singular, bronchus). These tubes also have smooth muscle and cartilage rings. The bronchi branch into smaller bronchioles, forming a bronchial “tree.” The bronchioles terminate in the air sacs known as alveoli. Lungs
Human lungs are composed of approximately 300 million alveoli, which are cup-shaped sacs surrounded by a capillary network. Red blood cells pass through the...
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