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The Respiratory System

  • Respiration is the process through which gas exchange occurs. During respiration, animals take in oxygen and release carbon dioxide.
  • Gas exchange in simple aquatic animals occurs via diffusion across the whole surface of the body. In more complex aquatic animals, gills provide a surface across which gas exchange can occur.
  • Some animals rely on diffusion across the skin for gas exchange. More complex animals have internal respiratory surfaces that include branched tubes or folded structures.
  • In insects, air enters the body through small openings called spiracles. Air then passes into air ducts called tracheae, which branch into tracheoles that reach the cells of the body so that gas exchange can occur.
  • In mammals, air enters the nasal cavity, passes through the pharynx and larynx and then into the trachea. Next, the air enters the bronchi, which branch into bronchioles, ending in alveoli, the site of gas exchange.
  • Ventilation occurs during the process of breathing. During inspiration, air is pulled into the lungs by the negative pressure created when the thoracic cavity expands. The reverse process occurs during expiration.

The Respiratory System

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AP Biology Intro