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Gas Exchange and Breathing

Gas Exchange and Breathing. Characteristics of a Gas Exchange Surface Structure and Functioning of the Gas Exchange System. The Need for Gas Exchange and Ventilation. In humans O 2 is used in cell respiration (in cytoplasm and mitochondria) and CO 2 is released

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Gas Exchange and Breathing

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  1. Gas Exchange and Breathing Characteristics of a Gas Exchange Surface Structure and Functioning of the Gas Exchange System

  2. The Need for Gas Exchange and Ventilation • In humans O2 is used in cell respiration (in cytoplasm and mitochondria) and CO2 is released • Gas exchange happens in the alveoli of human lungs: O2 diffuses from the air into the alveoli to blood capillaries, CO2 diffuses in opposite direction • A ventilation system maintains a high conc. Of O2 in the alveoli • Ventilation in humans is produced by changes in pressure in the chest cavity. Changes in pressure are carried out by the action of two sets of muscles in the breathing apparatus: diaphragm and the intercostal muscles

  3. How are alveoli adapted to gas exchange?

  4. Adaptations of the alveoli to gas exchange • Alveoli are small (~100 um in diameter) but the lungs contain hundreds of millions of alveoli (huge overall surface area for gas exchange) • Walls of the alveoli and capillaries consist of a single layer • The capillaries surrounding the alveoli contain high CO2 and low O2 concentration • Cells in the alveolus secrete a fluid which helps keep the walls moist facilitating gas diffusion • The walls of the alveoli produce a natural detergent that prevents the walls from sticking together. Certain alveolar cells synthesize a mixture of lipoproteins called surfactant (secreted into alveolar air spaces continuously, reduces surface tension thus decreasing tendency of alveoli to collapse

  5. Ventilation of the Lungs • Air is inhaled into the lungs through trachea, bronchi and bronchioles • Air is exhaled via the same route • What are the structures involved in gas exchange???

  6. Gas Exchange Structures

  7. Structures of the Gas Exchange System (cont…)

  8. INHALING The external intercostal muscles contract, raising the ribs and elevating sternum The diaphragm contracts becoming flatter and moving downwards The muscle movements increase the volume of the thorax. Lungs expand, partial lung pressure decreases The pressure inside the thorax therefore drops below atmospheric pressure Air flows into the lungs from outside the body until the pressure inside the lungs rises to atmospheric pressure EXHALING The internal intercostal muscles relax following inhalation. Abdominal organs spring back to original shape, moving the ribcage down and in The diaphragm pushes up into a dome shape The muscle movement decrease the volume of the thorax. Lungs contract, partial lung pressure increases Therefore pressure inside the thorax rises above atmospheric pressure Air flows out from lungs to outside of the body. Lung pressure falls below atmospheric pressure Ventilation of the Lungs

  9. Self-planned laboratory • How does exercise affect the functioning of the heart and lungs • Exercise increases cardiac output • Cardiac output = stroke volume X heartrate • Stroke volume = volume of blood ejected by the ventricles in one beat

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