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External Respiration – Specifics

Gas Partial Pressure. Surrounding Air, mm Hg. Alveolus, mm Hg. P O 2. 159. 104 . P CO 2. 0.3 . 40. P H 2 O. 3.5. 47. External Respiration – Specifics. Partial pressures in alveoli different from atmospheric partial pressures. External Respiration: Reasons for Difference.

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External Respiration – Specifics

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  1. Gas Partial Pressure Surrounding Air, mm Hg Alveolus, mm Hg PO2 159 104 PCO2 0.3 40 PH2O 3.5 47 External Respiration – Specifics • Partial pressures in alveoli different from atmospheric partial pressures

  2. External Respiration: Reasons for Difference • humidification of inhaled air • gas movements • increases alveolar PCO2 • decreases alveolar PO2 • mixing of old and new air (not all alveolar air is exchanged with each breath)

  3. External Respiration:Gas Movements • O2 loading (into blood) • CO2 unloading (out of blood)

  4. Ventilation-Perfusion Coupling • circulatory system works in coordination with respiratory system to maximize effectiveness of exchange • PO2 in bronchioles affects arteriolar diameter – more blood goes to areas with higher oxygen levels • decreased airflow  decreased PO2 in airway  vasoconstriction of pulmonary arterioles • increased airflow  increased PO2 in airway  vasodilation of pulmonary arterioles

  5. Ventilation-Perfusion Coupling • PCO2 in bronchioles affects bronchiolar diameter – areas that are stagnating build up CO2 increase flow through those areas • decreased airflow  increased PCO2 in airway  bronchodilation • increased airflow  decreased PCO2 in airway  bronchoconstriction

  6. Internal Respiration: Gas Movements • O2 enters tissues from blood • CO2 leaves tissues to enter blood

  7. Factors Affecting Internal Respiration • surface area for exchange • size of capillary bed[s] serving tissue • varies from tissue to tissue • partial pressure gradient between blood and tissue • ventilation keeps arterial PO2 high, PCO2 low • rate of blood flow • varies with needs of tissue • increases during activity • decreases when tissue is inactive

  8. Metabolism Review • Aerobic: Glucose + 6 O2 --> 6 CO2 + 6 H2O + ATP • Anaerobic: Glucose --> lactic acid + ATP • By-products of glucose catabolism include: • BPG (bis-phosphoglycerate; intermediate of glycolysis) • heat (reactions are inefficient) • H+ (lowers pH), from: • CO2 combines with H2O to produce carbonic acid or • lactic acid

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