5B - Gas Transport and Ventilation/Perfusion Ratios Flashcards
What are the two forms that oxygen is carried in the blood?
- Bound to hemoglobin (~98.5% - most important)
2. Dissolved in plasma (~1.5%)
Normal adult hemoglobin is comprised of what subunits?
What state is iron in to bind O2?
a2b2
Ferrous state (Fe2+)
5b6. Hemoglobin-O2 Dissociation Curve
Arterial blood has a P(O2) of 100 mmHg. What is the level of oxygen saturation of hemoglobin at this point?
Hemoglobin is 98-100% saturated - Oxygen bound to all four heme groups on all hemoglobin molecules
5b6. Hemoglobin-O2 Dissociation Curve
Mixed venous blood has a P(O2) of 40 mmHg. What is the level of oxygen saturation of hemoglobin at this point?
Hemoglobin is 75% saturated - on average, 3 of the 4 heme groups on each hemoglobin have O2.
5b7. Hemoglobin-O2 Dissociation Curve
What is the level of oxygen saturation of hemoglobin at P(O2) of ~25 mmHg?
Hemoglobin is 50% saturated - on average, 2 of the 4 heme groups of each hemoglobin molecule have O2 bound
5b8. What is the shape of the hemoglobin-O2 dissociation curve? What do you call the relationship between PO2 and hemoglobin saturation? (what kind of cooperativity)?
Sigmoid shape
Positive cooperativity
5b10. What factors influence hemoglobin saturation at a given PO2?
P(CO2)
pH
Temperature
2,3-BPG Hemoglobin F
5b11. When will the hemoglobin-O2 dissociation curve shift to the right?
Increased P(CO2), decreased pH, increased temperature, or increased 2,3-BPG
5b11. When the hemoglobin-O2 dissociation graph shifts to the right, what does it mean for O2 unloading and for % saturation of hemoglobin?
O2 unloading from the arterial blood to tissues if facilitated
% saturation of hemoglobin is decreased
5b12. How does exercise affect the Hemoglobin-O2 dissociation curve?
Shifts to the right
- More CO2 produced
- Tissue pH decreased
- Temperature increased
- 2,3-DPG concentration incresaed
- Stimulates O2 delivery to exercising muscles
5b14. What is an adaptation that the body makes in reaction to chronic hypoxemia (living at high altitude)?
Increased synthesis of 2,3-BPG, which binds to hemoglobin and facilitates unloading of O2 in the tissues
5b16. What changes can trigger a hemoglobin-O2 dissociation curve shift to the left?
Decreased P(CO2)
Increased pH
Decreased temperature
Decreased 2,3-BPG concentration
5b15. When the hemoglobin-O2 dissociation curve shifts to the left, is unloading O2 from arterial blood to the tissues more or less difficult?
More difficult
At any level of P02 - the % saturation of hemoglobin is increased
5b17. Which has a higher affinity for hemoglobin - CO or O2?
CO has a 200x affinity for hemoglobin than does O2
CO will occupy O2 binding sites on hemoglobin and decrease the O2 concentration of blood.
5b17. Will binding of CO shift the curve to the left or right?
CO will shift the curve to the left, increasing the affinity of the remaining site for O2.
5b18. What is hypoxemia?
Decrease in arterial P(O2)
5b18. What is hypoxia?
Decreased O2 delivery to the tissues
5b18. What are the factors that affect the levels of O2 content in the blood?
Hemoglobin concentration
O2 binding capacity of hemoglobin
% saturation of hemoglobin by O2 (which depends on P O2)
5b18. What are three possible causes of hypoxia?
- Decreased cardiac output
- Decreased O2 - binding capacity of hemoglobin
- Decreased arterial P (O2)
5b19. What is anemic hypoxia?
Anemic hypoxia reflects poor O2 delivery resulting from too few RBC or from RBC that contain abnormal or too little hemoglobin
5b19. What causes ischemic (stagnant) hypoxia?
Impairment or blockage of blood circulation.
Congestive heart failure may cause body-wide ischemic hypoxia
5b19. What regions of the body are affected by ischemic hypoxia via:
- Congestive heart failure
- Emboli/thrombi
- Congestive heart failure may cause body-wide ischemic hypoxia
- Embolic or thrombi block oxygen delivery only to tissues distal to the obstruction
5b20. What is histotoxic hypoxia?
Occurs when body cells are unable to use O2 even though adequate amounts are delivered.
5b20. What kind of hypoxia results from the use of metabolic poisons, like cyanide?
Histotoxic hypoxia
5b20. What is hypoxemic hypoxia?
- Possible causes?
Reduced arterial P(O2).
- Disordered/abnormal ventilation-perfusion coupling
- Pulmonary diseases that impair ventilation
- Breathing air containing scant amounts of O2
5b21. What are the three forms that carbon dioxide is carried to the lungs?
- HCO3 (bicarbonate) - major form (70-90%) - from hydration of CO2 in RBC
- Dissolved CO2, free in solution (small amount)
- Carbaminohemoglobin - CO2 bound to hemoglobin (small amount)
5b22. What is chloride shift in RBC in tissue?
HCO3 diffuses out of RBC in exchange for Cl- in order for the cell to maintain its osmotic equilibrium and prevent RBC shrinkage
5b22. What is chloride shift in RBC at the lungs?
Cl leaves the RBC and HCO3 comes back in and is then converted into CO2 for exit out of the lungs
5b23. What is V/Q ratio?
V/Q ratio - Ventilation-Perfusion ratio
The ratio of alveolar ventilation (V) to pulmonary blood flow (Q) Ventilation and perfusion matching is important to achieve ideal exchange of O2 and CO2.
5b23. If frequency, tidal volume, and cardiac output are normal, what is the V/Q ratio?
- What is arterial P(O2)?
- What is arterial P(CO2)?
V/Q ratio - 0.8
Arterial P(O2) - 100 mm Hg Arterial P(CO2) - 40 mm Hg
5b24. What accounts for differences in V/Q ratio throughout the body?
Various parts of the lung have different V/Q ratio due to gravity.
Local changes in V/Q ratio are common in disease
5b24. What happens if the V/Q ratio is too high?
Perfusion is reduced relative to ventilation
Alveolar p(O2) will rise because less O2 enters the blood
Alveolar p(CO2) will fall because less CO2 is delivered
5b24. What happens if the V/Q ratio is too low?
Ventilation to an alveolus is reduced relative to its perfusion
Alveolar p(O2) falls because less O2 is delivered Alveolar p(CO2) rises because less CO2 is expired
5b25. What is V/Q ratio when airways are completely blocked?
Ventilation is zero, which means V/Q ratio is zero.
Called a shunt.
No gas exchange, but the P(O2) and P(CO2) of pulmonary capillary blood will approach its regular values in mixed venous blood.
5b26. What is V/Q ratio when there is a pulmonary embolus (dead space)?
Perfusion is zero, which means V/Q ratio is infinite
No gas exchange in lung, but alveoli will approach their regular P(O2) and P(CO2).
