EXAM III: 5B Gas transport & Ventiliation/Perfusion Ratios Flashcards
What are the components of Hemoglobin?
-Each subunit contains a heme moiety
- Iron is in the ferrous state (Fe+2) which binds O2
- Normal adult hemoglobin = alpha 2 beta 2
Which two forms is oxygen carried ?
1) Dissolved in plasma (1.5%)
2) Bound to hemoglobin (most important; 98.5%)
***Hemoglobin increases the O2 carrying capacity of blood 70X
At a P O2 of 100mm Hg(arterial) how much of Hemoglobin saturated?
- 98-100% saturated.
- O2 is bound to all 3 heme groups on all hemoglobin molecules
At a P O2 of 40mm Hg(mixed venous blood) how much of Hemoglobin saturated?
Hemoglobin is 75% saturated
-On average, 3 of the 4 heme groups on each hemoglobin molecule have O2 bound.
At a P O2 of 25mm Hg(arterial) how much of Hemoglobin saturated?
Hemoglobin is 50% saturated; on average 2 of the 4 groups of each hemoglobin molecules have O2 bound.
Why does the Hemoglobin O2 dissociation curve sigmoidal shaped?
The curve is the result of a change in the affinity of hemoglobin as each successive O2 molecule binds to the heme site( positive Cooperativity)
-Binding of the 1st O2 molec. increases affinity for more.
What does the change of affinity facilitate?
The loading of O2 in the lungs(flat portion of curve) & the unloading of O2 at the tissues (steep portion of the curve)
At the pulmonary capillaries is the Venous or Arterial end have a higher pressure?
The venous end (104 mmHg) has a higher P O2.
This is equal to the Alveolus P O2 (104 mmHg)
At the systemic capillaries is the Venous or Arterial end have a higher pressure?
At the Arterial end
What influences the hemoglobin saturation at a given P o2.?
1) temperature
2) blood pH
3) P CO2
4) 2,3 DPG
How does 2, 3 BPG bind?
Binds irreversibly with hemoglobin, produced by RBCs as they break down glucose buy glycolysis.
When does the curve shift to the RIGHT?
- When the affinity of hemoglobin for O2 is decreased.
- P 50 is increased & unloading of O2 from arterial blood to the tissue is facilitated.
- For any level the PO2, the % saturation of hemoglobin is decreaed.
How does the shift to the right affect the affinity?
Decreases the affinity of hemoglobin for O2 and facilitates the unloading of O2 in the tissues (Bohr Effect)
***increase in PCO2 or decreases in pH
During exercise how is CO2, O2, and pH affected?
- tissues make more Co2
- decreases pH (through Bohr affect),
- Stimulates O2 delivery to the muscles
Shift to the right for dissociated curve affects temperature how?
- Increases in temperature (e.g during exercise)
- dec affinity of hemoglobin for O2 and facilitates delivery of O2 to tissues during demand.
How does shifting to the right affect 2,3 DPG concentration?
- Increases 2,3 DPG concentration.
- Binds to the beta chains of deoxyhemoglobin and decreases the affinity of hemoglobin for O2.
How does living at at a high altitude affect affect 2,3 DPG concentration?
The adaptation to chronic hypoxemia increases synthesis of 2, 3 DPG which binds to hemoglobin & facilitates the unloading of O2 to tissues.
When does the curve shift to the left ?
-Occurs when the affinity of hemoglobin for O2 is INCREASED.
- P50 is decreased, and unloading of O2 from arterial blood into the tissues is more difficult
- For any level of PO2 the % saturation of hemoglobin is INCREASED.
What causes the shift to the left in the dissociation curves?
1) decreased PCO2
2) increased pH
3) decreased temperature
4) decreased 2, 3 DPG concentration
How is the affinity for CO on hemoglobin compare to O2?
CO competes for O2 binding sites; Affinity of hemoglobin for CO is 200X greater than O2.
- CO occupies O2 binding sites, thus decreases the O2 concentration of blood
- Bind of CO to hemoglobin increases the affinity of remaining sire for O2 causing the shift to left.
What is Hypoxemia?
What is Hypoxia?
Hypoxemia is a DECREASE in arterial P O2
Hypoxia is DECREASED O2 delivery to the tissues
What does the content of blood depend on?
1) Hemoglobin concentration,
2) O2 binding capacity of hemoglobin
3) % saturation of hemoglobin by O2 (which depends on PO2)
What can Hypoxia be caused by?
1) Decreased cardiac output
2) decreased O2 binding capacity of hemoglobin
3) decreased arterial P O2
What are the 4 types of Hypoxia?
1) Anemic
2) Ischemic (Stagnant)
3) Histotoxic
4) Hypoxemia
What is Anemic hypoxia?
Reflects poor O2 delivery resulting from too few RBCs or from RBCs that contain abnormal or too little Hb.
What is ischemic (stagnant) hypoxia?
Results when blood circulation is impaired or blocked.
Congestive heart failure may cause body-wide ischemic hypoxia, whereas emboli or thrombi block oxygen delivery only to tissues distal to obstruction.
What is Histotoxic hypoxia?
Occurs when body cells are unable to use O2 even though adequate amounts are delivered.
-Result of Metabolic poisons like cyanide or CO.
What is Hypoxemia hypoxia?
indicated by the reduced arterial PO2
Causes: disordered or abnormal Ventilation-perfusion coupling, pulmonary disease that impair ventilation, breathing air containing scant amounts of O2.
What 3 forms is the CO2 carried to the lungs in venous blood?
1) Dissolved CO2 (small amt) which is free in solution
2) Carbaminohemoglobin (small amt) which is CO2 bound to hemoglobin
3) HCO3- (from hydration of CO2 in the RBCs ) which is the ****MAJOR FORM (70-90%)
What is the Chloride Shift?
HCO3- diffuses out to the red blood cell in exchange for CL- which helps the cell maintain its osmotic equilibrium.
Where does the Chloride Shift occur in the Lungs?
Occur sin the opposite direction, as CL- leaves the RBC when HCO2- enters to be converted back to CO2
What is the Ventilation-Perfusion Ration (V/Q Ration)?
Is the ration of alveolar Ventilation (V) to pulmonary blood flow (Q).
** Ventilation and Perfusion matching is important to achieve the ideal exchange of O2 and CO2
If the frequency, tidal volume, and cardiac output are normal, the V/Q ratio is approximately _________
0.8 (4.2 L/min Ventilation divided by 5.5 L/min blood flow)
*** This ratio results in an arterial PO2 of 100 mm Hg and an arterial P CO2 of 40 mm Hg.
If the ventilation to an alveolus is reduced relative to its perfusion, what happens to the PO2?
The PO2 in the alveolus falls because less O2 is delivered to it and the alveolar PCO2 rises because less CO2 is expired.
IF perfusion is reduced relative to ventilation what happens to PO2?
The alveolar PCO2 falls because less CO2 is delivered and the alveolar PO2 rises because less O2 enters the blood
How is the V/Q ration affected in airway obstruction?
- IF the airways is completely blocked (e.g. food caught in trachea) then ventilation is ZERO.
- If blood flow is Normal then V/Q is ZERO = Shunt!
Is there gas exchange in a lung that is perfused but not ventilated? Explain
- No gas exchange.
- The PO2 and PCO2 of pulmonary capillary blood (and therefore of systemic arterial blood) will approach their values in mixed venous blood.
How is the V/Q ratio affected in Pulmonary Embolism
If blood flow to a lung is completely block (embolism occluding pulmonary artery) then blood flow to that lung is ZERO
What is dead space?
During pulmonary embolism, If ventilation is normal, then V/Q is infinite
Is there gas exchange in a lung that is ventilated but not perfused? Explain
- No gas exchange
- The PO2 and PCO2 of alveolar gas will approach their values in inspired air.
