Costanzo | Physiology | Chapter 5 | Respiratory Physiology | Study Guide
Chapter 5: Respiratory Physiology Notes
I. Structure of the Respiratory System
Conducting Zone: Includes the nose, pharynx, larynx, trachea, bronchi, and bronchioles. Its functions are to warm, filter, and humidify inspired air. It contains cilia and smooth muscle but lacks alveoli, meaning no gas exchange occurs here (anatomic dead space) [185, 186f].
Respiratory Zone: Includes respiratory bronchioles, alveolar ducts, and alveoli. This is the site of gas exchange.
Alveoli: Lined with Type I and Type II pneumocytes. Type II cells synthesize surfactant, which reduces surface tension.
II. Lung Volumes and Capacities
Static Volumes:
Tidal Volume (VT): Volume inspired/expired in a normal breath (500 mL) [187, 450t].
Inspiratory Reserve Volume (IRV): Extra volume inspired above VT (3000 mL).
Expiratory Reserve Volume (ERV): Extra volume expired below VT (1200 mL).
Residual Volume (RV): Volume remaining after maximal expiration (1200 mL); cannot be measured by spirometry.
Capacities:
Functional Residual Capacity (FRC): ERV + RV. The equilibrium volume where the collapsing force of the lungs equals the expanding force of the chest wall.
Vital Capacity (VC): IC + ERV. Maximal volume that can be expired after maximal inspiration.
Total Lung Capacity (TLC): All volumes combined.
III. Mechanics of Breathing
Muscles: Diaphragm is the most important for inspiration. Expiration is normally passive due to elastic recoil.
Compliance: The ease with which the lungs expand (ΔV/ΔP). Compliance is increased in emphysema and decreased in fibrosis or lack of surfactant.
Surfactant: Composed of DPPC. It increases compliance and prevents small alveoli from collapsing into large ones (Law of Laplace).
Resistance: Airway resistance is determined by the Poiseuille relationship; the medium-sized bronchi are the site of highest resistance.
IV. Gas Exchange
Diffusion: Gas transfer occurs by simple diffusion (Fick’s Law). It is proportional to surface area and partial pressure gradients, and inversely proportional to thickness.
Perfusion vs. Diffusion Limitation:
Perfusion-limited: Gas equilibrates before the end of the capillary (e.g., N2O, normally O2).
Diffusion-limited: Gas does not equilibrate (e.g., CO, O2 during strenuous exercise or in fibrosis).
V. Oxygen and Carbon Dioxide Transport
Oxygen: 98% is bound to hemoglobin (Hb). The sigmoidal curve shows positive cooperativity.
Shift Right (easier unloading): ↑PCO2,↑H+(↓pH),↑Temp,↑2,3-DPG [216, 513f, 519-521].
Shift Left (tighter binding): ↓PCO2,↓H+,↓Temp,↓2,3-DPG,HbF, and CO [216, 513f, 515-517, 523].
Carbon Dioxide: Transported as dissolved CO2 (7%), carbaminohemoglobin (23%), and bicarbonate (HCO3−, 70%).
VI. Ventilation/Perfusion (V/Q) Relationships
Regional Variation: Both V and Q are higher at the base of the lung than the apex. However, V/Q is highest at the apex and lowest at the base.
V/Q Defects:
Dead Space (V/Q=∞): Ventilation without perfusion (e.g., pulmonary embolism).
Shunt (V/Q=0): Perfusion without ventilation (e.g., airway obstruction).
VII. Control of Breathing
Brain Stem: Medullary respiratory center (inspiratory and expiratory centers).
Chemoreceptors:
Central: Located in the medulla; respond to decreased pH in CSF (reflecting PaCO2).
Peripheral: Located in carotid and aortic bodies; respond to PaO2<60 mmHg, ↑PaCO2, and ↓pH.
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Chapter 5 Study Guide
I. Glossary of Key Terms
A-a Gradient: The difference between alveolar and arterial PO2; used to diagnose the cause of hypoxemia.
Bohr Effect: The effect of H+ and CO2 on the O2-hemoglobin dissociation curve (right shift).
Chloride Shift: The exchange of HCO3− for Cl− across the red blood cell membrane.
Dead Space: Volume of air that does not participate in gas exchange.
Haldane Effect: The effect of O2 on CO2 transport; deoxygenation of Hb increases its CO2 carrying capacity.
Hysteresis: The difference between the inspiration and expiration curves on a pressure-volume loop.
Hypoxemia: A decrease in arterial PO2 [234, 558t].
Hypoxia: A decrease in O2 delivery to the tissues.
Minute Ventilation: The total volume of air moved into and out of the lungs per minute (VT×breaths/min).
Surfactant: A mixture containing DPPC that reduces surface tension in alveoli.
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II. 50 Question-and-Answer Quiz
Questions
Which zone of the lung contains no alveoli?
What is the main muscle of inspiration?
Which lung volume cannot be measured by spirometry?
What is the formula for Functional Residual Capacity (FRC)?
What happens to lung compliance in emphysema?
What is the major constituent of surfactant?
Which cells produce surfactant?
Is normal expiration active or passive?
Which law states that pressure is inversely proportional to volume?
What is the value of normal tidal volume (VT)?
What is anatomic dead space?
How do you calculate alveolar ventilation?
Which equation predicts alveolar PO2?
What defines "physiologic dead space"?
What is the partial pressure of O2 in dry inspired air at sea level?
What is the PaO2 of systemic arterial blood?
What is the PaCO2 of systemic arterial blood?
Which gas is used to measure the diffusing capacity of the lung (DL)?
Is N2O transfer diffusion-limited or perfusion-limited?
When is O2 transfer diffusion-limited?
What is the normal O2-binding capacity of 1g of hemoglobin?
What percentage of O2 is transported bound to hemoglobin?
What does P50 represent?
Name four factors that shift the O2-Hb curve to the right.
How does carbon monoxide affect the O2-Hb curve?
Which type of hemoglobin has a higher affinity for O2 than HbA?
What is the major form of CO2 transport in blood?
Which enzyme catalyzes CO2+H2O→H2CO3?
Where is V/Q the highest in the lung?
What is a "shunt"?
What is the V/Q ratio in dead space?
What is the primary stimulus for central chemoreceptors?
At what PaO2 do peripheral chemoreceptors become stimulated?
Which nerve carries sensory info from carotid body chemoreceptors?
What is the "apneustic center" function?
Where is the inspiratory center located?
How does the body adapt to high altitude (ventilation-wise)?
What is polycythemia?
What is the effect of 2,3-DPG on hemoglobin affinity?
How does high altitude affect pulmonary artery pressure?
What defines hypoxemia?
Does hypoventilation increase or decrease PaCO2?
What is the A-a gradient in a person at high altitude?
Which condition causes an increased A-a gradient: high altitude or fibrosis?
What is the "Bohr effect"?
What is the "Haldane effect"?
How does exercise affect the O2-Hb curve?
What are J receptors?
Which part of the lung has the highest blood flow (Q)?
What is the normal V/Q ratio for the whole lung?
Answer Key
Conducting zone. 2. Diaphragm. 3. Residual Volume (RV). 4. ERV+RV. 5. Increased. 6. DPPC. 7. Type II pneumocytes. 8. Passive. 9. Boyle's Law. 10. 500 mL. 11. Volume of the conducting airways. 12. (VT−VD)×breaths/min. 13. Alveolar Gas Equation. 14. Anatomic dead space + alveolar dead space. 15. 160 mmHg. 16. 100 mmHg. 17. 40 mmHg. 18. Carbon monoxide (CO). 19. Perfusion-limited. 20. Strenuous exercise, high altitude, or fibrosis. 21. 1.34 mL O2. 22. 98%. 23. PO2 at 50% Hb saturation. 24. ↑PCO2,↑H+,↑Temp,↑2,3-DPG. 25. Decreases binding sites and shifts curve left. 26. HbF (fetal). 27. HCO3−. 28. Carbonic anhydrase. 29. Apex. 30. Perfusion without ventilation (V/Q=0). 31. Infinity (∞). 32. ↓pH in CSF. 33. <60 mmHg. 34. CN IX (glossopharyngeal). 35. Prolongs inspiration. 36. Medulla (DRG). 37. Hyperventilation. 38. Increased RBC concentration. 39. Decreases affinity (shifts right). 40. Increases it (vasoconstriction). 41. ↓PaO2. 42. Increase. 43. Normal (near zero). 44. Fibrosis. 45. H+/CO2 effect on Hb-O2 affinity. 46. O2 effect on Hb-CO2 affinity. 47. Shifts it right. 48. Receptors in alveolar walls. 49. Base. 50. 0.8.
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III. Short Answer Questions
Explain why Residual Volume cannot be measured by simple spirometry.
Answer: Spirometry only measures air that can be moved into or out of the lungs. Since Residual Volume is the air that remains in the lungs even after a maximal forced expiration, it cannot be exhaled into the spirometer.
Describe the role of 2,3-DPG in high altitude adaptation.
Answer: Chronic hypoxia at high altitude stimulates 2,3-DPG production. 2,3-DPG binds to the β chains of deoxyhemoglobin, decreasing Hb affinity for O2. This shifts the dissociation curve to the right, facilitating the unloading of O2 to the tissues.
Contrast "Dead Space" and "Shunt."
Answer: Dead space is ventilation of lung regions that are not perfused (V/Q=∞), such as in a pulmonary embolism. A shunt is perfusion of lung regions that are not ventilated (V/Q=0), such as in an airway obstruction.
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IV. Essay Questions
Describe the coordinated respiratory and cardiovascular changes that occur during a climb to high altitude.
Focus: Discuss the initial trigger (decreased Patm and PIO2), the peripheral chemoreceptor response (hyperventilation), the resulting respiratory alkalosis, the renal compensation (excreting HCO3−), the production of 2,3-DPG, polycythemia (via EPO), and hypoxic pulmonary vasoconstriction.
Explain the sigmoidal shape of the O2-hemoglobin dissociation curve and the physiological significance of its flat and steep portions.
Focus: Define positive cooperativity. Explain that the flat portion (PO2 60-100 mmHg) ensures high O2 loading even if alveolar PO2 drops slightly. The steep portion (PO2<40 mmHg) allows for the rapid unloading of large amounts of O2 to tissues with small changes in PO2.
