Human Respiratory System

  •  A pair of external nostrils open out above the upper lips. It leads to a nasal chamber through the nasal passage. The nasal chamber opens into pharynx, a portion of which is the common passage for food and air. The pharynx opens into larynx through slit like aperture, the glottis.
  • During swallowing glottis gets covered by a thin elastic cartilaginous flap called epiglottis to prevent the entry of food into the larynx. Larynx is a cartilaginous box which helps in sound production hence also called sound box.
  •  Trachea is a straight tube extending up to the mid-thoracic cavity, which divides into right and left primary bronchi. Each bronchus undergoes repeated divisions to form the secondary and tertiary bronchi and bronchioles ending up in very thin terminal bronchioles. Trachea till tertiary bronchi are supported by incomplete cartilaginous rings. Each terminal bronchiole gives rise to a number of very thin, irregular-walled and vascularised bag-like structure called alveoli. Due to very intimate contact of blood capillaries with the alveoli, the exchange of gases takes place easily. The number of alveoli in human lungs has been estimated to be approximately 300 million.
  • The lungs lie in the thoracic cavity on the sides of the heart. Each lung is enclosed within double layered, pleura. A very narrow space called pleural cavity exists between the two pleura. It contains a watery fluid, the pleural fluid, secreted by the pleura. It lubricates the pleura so that they may slide over each other without friction as the lungs expand and contract during respiration.
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