EXAM III: 5B Gas transport & Ventiliation/Perfusion Ratios

Question 0

What are the components of Hemoglobin?

Answer 0

-Each subunit contains a heme moiety

• Iron is in the ferrous state (Fe+2) which binds O2
• Normal adult hemoglobin = alpha 2 beta 2

Question 1

Which two forms is oxygen carried ?

Answer 1

1) Dissolved in plasma (1.5%)
2) Bound to hemoglobin (most important; 98.5%)

***Hemoglobin increases the O2 carrying capacity of blood 70X

Question 2

At a P O2 of 100mm Hg(arterial) how much of Hemoglobin saturated?

Answer 2

• 98-100% saturated.

- O2 is bound to all 3 heme groups on all hemoglobin molecules

Question 3

At a P O2 of 40mm Hg(mixed venous blood) how much of Hemoglobin saturated?

Answer 3

Hemoglobin is 75% saturated

-On average, 3 of the 4 heme groups on each hemoglobin molecule have O2 bound.

Question 4

At a P O2 of 25mm Hg(arterial) how much of Hemoglobin saturated?

Answer 4

Hemoglobin is 50% saturated; on average 2 of the 4 groups of each hemoglobin molecules have O2 bound.

Question 5

Why does the Hemoglobin O2 dissociation curve sigmoidal shaped?

Answer 5

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.

Question 6

What does the change of affinity facilitate?

Answer 6

The loading of O2 in the lungs(flat portion of curve) & the unloading of O2 at the tissues (steep portion of the curve)

Question 7

At the pulmonary capillaries is the Venous or Arterial end have a higher pressure?

Answer 7

The venous end (104 mmHg) has a higher P O2.

This is equal to the Alveolus P O2 (104 mmHg)

Question 8

At the systemic capillaries is the Venous or Arterial end have a higher pressure?

Answer 8

At the Arterial end

Question 9

What influences the hemoglobin saturation at a given P o2.?

Answer 9

1) temperature
2) blood pH
3) P CO2
4) 2,3 DPG

Question 10

How does 2, 3 BPG bind?

Answer 10

Binds irreversibly with hemoglobin, produced by RBCs as they break down glucose buy glycolysis.

Question 11

When does the curve shift to the RIGHT?

Answer 11

• 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.

Question 12

How does the shift to the right affect the affinity?

Answer 12

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

Question 13

During exercise how is CO2, O2, and pH affected?

Answer 13

• tissues make more Co2
• decreases pH (through Bohr affect),
• Stimulates O2 delivery to the muscles

Question 14

Shift to the right for dissociated curve affects temperature how?

Answer 14

• Increases in temperature (e.g during exercise)

- dec affinity of hemoglobin for O2 and facilitates delivery of O2 to tissues during demand.

Question 15

How does shifting to the right affect 2,3 DPG concentration?

Answer 15

• Increases 2,3 DPG concentration.

- Binds to the beta chains of deoxyhemoglobin and decreases the affinity of hemoglobin for O2.

Question 16

How does living at at a high altitude affect affect 2,3 DPG concentration?

Answer 16

The adaptation to chronic hypoxemia increases synthesis of 2, 3 DPG which binds to hemoglobin & facilitates the unloading of O2 to tissues.

Question 17

When does the curve shift to the left ?

Answer 17

-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.

Question 18

What causes the shift to the left in the dissociation curves?

Answer 18

1) decreased PCO2
2) increased pH
3) decreased temperature
4) decreased 2, 3 DPG concentration

Question 19

How is the affinity for CO on hemoglobin compare to O2?

Answer 19

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.

Question 20

What is Hypoxemia?

What is Hypoxia?

Answer 20

Hypoxemia is a DECREASE in arterial P O2

Hypoxia is DECREASED O2 delivery to the tissues

Question 21

What does the content of blood depend on?

Answer 21

1) Hemoglobin concentration,
2) O2 binding capacity of hemoglobin
3) % saturation of hemoglobin by O2 (which depends on PO2)

Question 22

What can Hypoxia be caused by?

Answer 22

1) Decreased cardiac output
2) decreased O2 binding capacity of hemoglobin
3) decreased arterial P O2

Question 23

What are the 4 types of Hypoxia?

Answer 23

1) Anemic
2) Ischemic (Stagnant)
3) Histotoxic
4) Hypoxemia

Question 24

What is Anemic hypoxia?

Answer 24

Reflects poor O2 delivery resulting from too few RBCs or from RBCs that contain abnormal or too little Hb.

Question 25

What is ischemic (stagnant) hypoxia?

Answer 25

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.

Question 26

What is Histotoxic hypoxia?

Answer 26

Occurs when body cells are unable to use O2 even though adequate amounts are delivered.
-Result of Metabolic poisons like cyanide or CO.

Question 27

What is Hypoxemia hypoxia?

Answer 27

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.

Question 28

What 3 forms is the CO2 carried to the lungs in venous blood?

Answer 28

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%)

Question 29

What is the Chloride Shift?

Answer 29

HCO3- diffuses out to the red blood cell in exchange for CL- which helps the cell maintain its osmotic equilibrium.

Question 30

Where does the Chloride Shift occur in the Lungs?

Answer 30

Occur sin the opposite direction, as CL- leaves the RBC when HCO2- enters to be converted back to CO2

Question 31

What is the Ventilation-Perfusion Ration (V/Q Ration)?

Answer 31

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

Question 32

If the frequency, tidal volume, and cardiac output are normal, the V/Q ratio is approximately _________

Answer 32

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.

Question 33

If the ventilation to an alveolus is reduced relative to its perfusion, what happens to the PO2?

Answer 33

The PO2 in the alveolus falls because less O2 is delivered to it and the alveolar PCO2 rises because less CO2 is expired.

Question 34

IF perfusion is reduced relative to ventilation what happens to PO2?

Answer 34

The alveolar PCO2 falls because less CO2 is delivered and the alveolar PO2 rises because less O2 enters the blood

Question 35

How is the V/Q ration affected in airway obstruction?

Answer 35

• 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!

Question 36

Is there gas exchange in a lung that is perfused but not ventilated? Explain

Answer 36

• 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.

Question 37

How is the V/Q ratio affected in Pulmonary Embolism

Answer 37

If blood flow to a lung is completely block (embolism occluding pulmonary artery) then blood flow to that lung is ZERO

Question 38

What is dead space?

Answer 38

During pulmonary embolism, If ventilation is normal, then V/Q is infinite

Question 39

Is there gas exchange in a lung that is ventilated but not perfused? Explain

Answer 39

• No gas exchange

- The PO2 and PCO2 of alveolar gas will approach their values in inspired air.