Respiration System

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Respiration System
2012-02-05 12:08:54
Respiration System

Respiration System
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  1. Three requirements that facilitate diffusion
    • Respiratory surfaces remain moist so that gases can diffuse across cell membranes
    • The cells lining respiratory surfaces are very thin, to facilitate diffusion of gases through them
    • Respiratory systems have a sufficiently large surface area to allow adequate gas exchange

  2. Bulk Flow and Diffusion
    • Air moves past a respiratory surface by bulk flow : breathing
    • O2 and CO2 are exchanged through the respiratory surface by diffusion
    • O2 diffuse into the capillaries of the circulatory system
    • and CO2 diffuses out

  3. The human respiratory system can be divided into two parts
    • The conducting portion, a series of passageways that carry air into and out for gas-exchange
    • The gas-exchange portion, where gases are exchanged with the blood in tiny sacs within the lungs, alveoli

  4. Conducting Portion
    • carries air to the lungs
    • contains the apparatus that makes speaking possible
    • air enters through the nose or mouth
    • through the nasal or oral cavity into pharynx
    • to the larynx-sounds are produced by vocal chords
    • opening to the larynx is guarded by the epiglottis
    • air travels past the larynx into the trachea
    • trachea splits into two bronchi, each leading to lung
    • Inside the lung, each bronchus branches repeatedly into ever small tubes called bronchioles
    • Bronchioles lead to microscopic alveoli

  5. Gas Exchange Portion
    • Gas exchange occurs in the alveoli
    • Alveoli cluster around the end of each bronchiole like a bunch of grapes, providing a huge surface area for diffusion (~1,500 square feet)
    • A network of capillaries covers most of the alveolar surface
    • The walls of the alveoli consist of a single thin layer of epithelial cells
    • alveolar walls and the adjacent capillary walls are each only one cell thick
    • gases diffuse only a short distance
    • The alveoli are coated with surfactant
    • Gases dissolve in this fluid as they pass in and out of the alveolar air

  6. CO2 and O2 is high where?
    • In the lungs, O2 is high and CO2 is low, whereas in body cells, CO2 is high and O2 is low

  7. Oxygen transport
    • ~90% of the O2 carried by the blood is bound to hemoglobin

    Each hemoglobin molecule can carry up to four O2 molecules, each bound to each of four iron-containing heme groups

    As oxygen binds hemoglobin, the protein changes its shape, which alters its color;

    • deoxygenated blood is bright cherry-red, and deoxygenated blood is maroon-red

  8. Carbon dioxide transport
    • CO2 in the body cells diffuses into nearby capillaries, then the bloodstream to the alveoli
    • Alveolar capillaries have a higher CO2 concentration than that of the alveolar air
    • Thus, CO2 diffuses down a concentration gradient into the alveolar air, which is then exhaled
    • CO2 is transported in the blood in three ways
    • As bicarbonate ions (70%)
    • Bound to hemoglobin (20%)
    • Dissolved in plasma as CO2 (10%)
  9. Bicarbonate ions (HCO3)
    • are formed in rbc when CO2 combines with water.
    • CO2 + H2O à CO2 + HCO3
    • The reaction is reversed as the blood flows through capillaries surrounding the alveoli, where CO2 is low:
    • H+ + HCO3 à CO2 + H2O

  10. Breathing occurs in two stages
    • Inhalation, when air is drawn into the lungs
    • Exhalation, when air is expelled from the lungs
  11. Inhalation
    • occurs when the chest cavity is enlarged
    • During inhalation, the diaphragm is contracted, which pulls it downward, and the rib muscles contract, lifting the ribs up and outward
  12. Exhalation
    • occurs spontaneously, when the muscles that cause inhalation are relaxed
    • As the diaphragm relaxes, it domes upward; at the same time, the ribs fall down and inward
    • Both of these movements decrease the size of the chest cavity and force air out of the lungs
  13. respiratory center
    • Breathing rate is controlled by the respiratory center of the brain
    • The respiratory center is located in the medulla
    • Breathing rate can be primarily modified by CO2 receptors located in the medulla that adjust the breathing rate to maintain a constant low level of CO2 in the blood, while also ensuring that O2 levels remain adequate
    • As a backup system, there are also O2 receptors in the aorta and carotid arteries that stimulate the respiratory center to increase the rate and depth of breathing if O2 levels in the blood drop