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Respiratory system

  1. Maximum resistance of airway is due to trachea ,but regulation of airway resistance by terminal bronchioles.
  2. Acute breathlessness at high altitude is due to C02 washout
  3. Expiration in quiet breathing is passive and requires no muscle activity.
  4. Compliance of lung is a measure of stretchability of lungs and hence its total capacity. It is the change in lung volume per unit change in airway pressure (ΔVΔ/P).
  5. Increased in lung compliance (TLC also increases) – Emphysema, old age
  6. Decreased in lung compliance (TLC also decreases) - Interstitial pulmonary fibrosis, interstitial lung disease, pulmonary congestion.
  7. Resistance to small airways is best measured by maximal mid expiratory flow rates (MMFR) followed by FEV2.
  8. Airway resistance during expiration is more than during inspiration due to dynamic collapse of airways.
  9. Slow and deep breathing is better than rapid and shallow breathing.
  10. Spirometery can not be used in a direct way to measure - functional residual capacity, (FRC), residual volume (RV) and total lung capacity (TLC). Helium dilution, plethysmography(Best), N2 washout methods used to measure them.
  11. V/Q ratio is low at the base and high at the apex. But both ventilation and perfusion are max. at the base.
  12. The unique feature of pulmonary vasculature is that the hypoxia cause Vasconstriction (where as in other system it produces vsodilation).
  13. A cherry red flush rather than cyanosis is caused by COHb (carboxy hemoglobin).
  14. In hypoxia, with the reduction of P02 cerebral blood flow increases (due to vaso dilatation) to maintain 02 delivary in the brain.
  15. Apnea is cessation or stoppage of respiration.
  16. Respiratory centre is inhibited during swallowing to prevent food aspiration.
  17. Hypocapnia does not stimulate either peripheral or central chemoreceptors. (Only hypercapnia does so).
  18. SURFACTANT is a mixture of dipalmitoylphosphatidyl choline (62%), phosphatidyl glycerol (5%) and other phospholipids, neutral lipids, protein (Fibrin) & carbohydrate.
  19. It is produced by type II pneumoyctes.
  20. It decreases alveolar surface tension & increase alveolar compliance and prevents collapse (Most important role).
  21. Deficiency leads to IRDS or Hyaline membrane disease, Patchy Atelectasis, Pulmonary alveolar proteinosis.
  22. Physiologically inactive angiotensin I is converted to the angiotensin II in the pulmonary circulation. It is most important metabolic function of lungs.
  23. Transport of C02 in the form of bicarbonate ions accounts for approximately 75% of transported carbon dioxide from the tissues to lungs . So C02 is transported as plasma HC03> carbamino compound > dissolved C02(0.3ml%).
  24. P50 is the P02 at which hemoglobin is half (50%) saturated with 02.
  25. The value of P50 is 25mm Hg (3.6Kpa).
  26. Fully saturated each gram of Hb contains 1.39ml of 02 (practically 1.34ml of 02)
  27. Hypocarbia due to hyperventilation shifts 02 dissociation curve towards left i.e, P50 decrease & oxygen affinity increase.
  28. Inspiration is an active process, which occurs due to contraction of inspiratory muscle and results in increased Intrathoracic volume. So the intrapleural pressure at the base of lung decrease to -6mmHg (which is normally -2.5mmHg, relative to atmosphere) and becomes more negative.
  29. 02 dissociation curve(ODC) is sigmoid curve. Hb can binds with four 02 molecule but Myoglobin with one 02

Left shift of ODC – (occurs in lung)

  1. Increase pH or alkalosis
  2. Decrease pC02
  3. Decrease temperature
  4. Decrease 2,3, BPG(DPG)
  5. CO
  6. HbF
  7. Stored blood

Right shift of ODC - Happens in peripheral tissues & muscles

  1. Decrease pH or acidosis
  2. Increase pC02
  3. Increase temperature
  4. Increase 2,3 BPG

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