Question 1

What is the normal amount of oxygen consumed by the tissues?

Accepted Answer

Normal tissue oxygen consumption ( $ \dot{v} $O₂) is about 250 mL/min when the body is at rest.

Question 2

What is the effect of transfusing banked blood stored with an acid-citrate dextrose anticoagulant?

Accepted Answer

Banked blood stored with an acid-citrate dextrose anticoagulant loses a considerable amount of 2,3-DPG over time. This increases Hb affinity for oxygen, decreasing oxygen availability to the tissues. Large trAnswerfusions of banked blood stored over several days can theoretically impair oxygen release to the tissues. In terms of the oxygen delivery rate to the body's tissues, the trAnswerfusion of 2,3-DPG-depleted blood is probably physiologically insignificant.

Question 3

Assuming a concentration of 15 g/dL, what will be the hemoglobin's oxygen-carrying capacity?

Accepted Answer

Assuming a concentration of 15 g/dL, hemoglobin's oxygen-carrying capacity (100% saturation) is 15 ´ 1.34 = 20.1 mL/dL.

Question 4

Which of the following terms describes the unoxygenated hemoglobin?

Accepted Answer

Combined with oxygen, hemoglobin is called oxyhemoglobin (HbO₂). Oxygen does not oxidize hemoglobin; rather, it oxygenates hemoglobin. Unoxygenated hemoglobin is called deoxyhemoglobin. The term "reduced hemoglobin," which is sometimes used, is chemically incorrect because iron remains in the ferrous (Fe⁺⁺) state.

Question 5

Which of the following are statements related to P₅₀? I.Normally, a PO₂ of 27 mm Hg produces an SO₂ of 50%. II.The P₅₀ is a measure of hemoglobin's affinity for oxygen. III.A normal P₅₀ is accurate when the blood temperature is 37° C, pH is 7.40, and PCO₂ is 40 mm Hg. IV.Normally, a PO₂ of 47 mm Hg produces an SO₂ of 50%.

Accepted Answer

The P₅₀ is a measure of hemoglobin's affinity for oxygen. Normally, a PO₂ of 27 mm Hg produces an SO₂ of 50% when the blood temperature is 37° C, pH is 7.40, and PCO₂ is 40 mm Hg.

Question 6

How many times the body tissues' resting requirement is oxygen delivery?

Accepted Answer

The oxygen delivery rate is normally about four times the body tissues' resting requirement.

Question 7

Under resting conditions, what percentage of the arterial oxygen content is extracted by the tissues?

Accepted Answer

The body's tissues extract about 25% of the arterial blood's oxygen content (about 5 mL/dL) under resting conditions.

Question 8

What is the name of the phenomenon associated with the decreased affinity of Hb for oxygen when PCO₂ is high?

Accepted Answer

The decreased affinity of hemoglobin for oxygen, or the right curve shift caused by high PCO₂, is known as the Bohr effect.

Question 9

Which of the following statements relate to the HbO₂equilibrium curve? I.Large PO₂ changes cause small to minimal changes in oxygen content, especially at the extreme flat right end (60 to 100 mm Hg). II.Small PO₂ changes cause large blood oxygen content changes in the middle, steep portion of the curve (20 to 60 mm Hg). III.Large PO₂ changes cause large changes in oxygen content at the extreme flatter ends of the curve, especially the flat right end (60 to 100 mm Hg). IV.Small PO₂ changes cause small blood oxygen content changes in the middle, steep portion of the curve (20 to 60 mm Hg).

Accepted Answer

Small PO₂ changes cause large blood oxygen content changes in the middle, steep portion of the curve (20 to 60 mm Hg). In contrast, large PO₂ changes cause small to minimal changes in oxygen content at the extreme flatter ends of the curve, especially the flat right end (60 to 100 mm Hg).

Question 10

What is the effect of a high P₅₀?

Accepted Answer

A high P₅₀ means hemoglobin's affinity for oxygen is decreased. Similarly, a low P₅₀ means hemoglobin's affinity for oxygen is increased, causing it to bind oxygen molecules more aggressively (i.e., in this situation, hemoglobin is more than 50% saturated with oxygen at a PO₂ of 27 mm Hg). In the alveoli where oxygen loading takes place, blood with a low P₅₀ (high oxygen affinity) is advantageous. Conversely, high hemoglobin affinity for oxygen is detrimental at the tissue level where oxygen release is required. Ideally, hemoglobin affinity for oxygen changes depending on whether loading or unloading is required.

Question 11

Which of the following factors affect oxygen delivery to the tissues? I.Hemoglobin concentration II.Arterial hemoglobin saturation with oxygen III.Cardiac output IV.PCO₂ level

Accepted Answer

Factors that affect oxygen delivery (O₂ DEL) to the tissues include (1) hemoglobin concentration, (2) arterial hemoglobin saturation with oxygen (this automatically takes the PaO₂ into account), and (3) cardiac output ( $\dot Q $1 ). Because hemoglobin concentration, saturation, and PaO₂ determine the CaO₂, O₂ DEL depends on CaO₂ and $\dot Q $

Question 12

Which of the following statements are true of oxygen transport? I.Hemoglobin allows whole blood to carry approximately 20 mL of oxygen per 100 mL of blood at the normal arterial PaO₂ of 100 mm Hg. II.Hemoglobin's capacity to carry oxygen is approximately 67 times more than the capacity of plasma alone when PaO? is 100 mm Hg. III.A normal cardiac output of 5 L/min delivers approximately 1000 mL of oxygen to the body's tissues each minute. IV.The amount of oxygen delivered is not enough to meet the tissues' resting requirement.

Accepted Answer

Hemoglobin allows whole blood (plasma plus cellular components) to carry approximately 20 mL of oxygen per 100 mL of blood at the normal arterial PaO? of 100 mm Hg. This is approximately 67 times more than the capacity of plasma alone when PaO? is 100 mm Hg ([20 mL/dL]/[0.3 mL/dL] = 66.6). Thus, a normal cardiac output ( Q ) of 5 L/min delivers approximately 1000 mL of oxygen to the body's tissues each minute. This is more than enough oxygen to meet the tissues' resting requirement, which is only 250 mL/min.

Question 13

Which of the following are normal values for hemoglobin saturations and oxygen partial pressures? I.Arterial oxygen saturation (SaO₂) is approximately 97.5%. II.PO₂ is 100 mm Hg at SaO₂ of 97.5%. III.Mixed venous oxygen saturation (S $ \bar{V} $ O₂) is normally 75%. IV. P$ \bar{V} $O₂ is 60 mm Hg at S$ \bar{V} $O₂ of 75%.

Accepted Answer

Arterial oxygen saturation (SaO₂) is approximately 97.5% at a normal arterial PO₂ of 100 mm Hg. Only 75% of the hemoglobin molecules in mixed venous blood are oxygenated. Mixed venous oxygen saturation (S $ \bar{V} $1 O₂) is therefore normally 75%, which corresponds to a P$ \bar{V} $O₂ of approximately 40 mm Hg.

Question 14

What is the normal amount of oxygen delivered to the tissues?

Accepted Answer

O₂ DEL, in milliliters per minute, is the product of CaO₂ (mL oxygen/100 mL blood) and $\dot Q $ (L/min). Because CaO₂ is expressed in milliliters of oxygen contained in 100 mL of blood (i.e., one-tenth of a liter), the amount of oxygen carried in 1000 mL (1 L) of blood is calculated as follows: (CaO₂ x 10 dL/L) = mL oxygen/L blood The cardiopulmonary system normally delivers approximately 1000 mL of oxygen to the tissues each minute at rest, as shown in Box 8-6.

Question 15

Where is the majority of oxygen in blood?

Accepted Answer

By far, the majority of oxygen in the blood is bound to hemoglobin inside the erythrocyte.

Question 16

Which of the following levels of PO₂ is associated with sharp decreases in oxygen saturation and content?

Accepted Answer

Health care personnel tend to be a bit more alarmed by a decrease in PaO₂ of this magnitude. The arterial oxygen content decreases only 5%. However, the PaO₂ of 60 mm Hg is on the "shoulder" of the curve. As the PO₂ falls below this point, sharp decreases in oxygen saturation and content occur for relatively small changes in PO₂.

Question 17

What is the normal amount of oxygen extracted by the tissues for each 100 mL of blood?

Accepted Answer

The arterial-venous oxygen content difference C(a- $ \bar{V} $ )O₂ is approximately 5 mL/dL (see Box 8-4). This meAnswer the systemic tissues at rest extract approximately 5 mL of oxygen from each 100 mL of blood, or approximately 25% of the CaO₂.

Question 18

Which of the following conditions decrease hemoglobin's affinity for oxygen? I.Increased blood PCO₂ II.Decreased blood pH III.Increased blood temperature IV.Decreased blood levels of the organic phosphate 2,3-DPG

Accepted Answer

Figure 8-10 lists the factors that cause a decrease in hemoglobin affinity (increased blood PCO₂; decreased blood pH; increased blood temperature; and increased blood levels of the organic phosphate 2,3-diphosphoglycerate [2,3-DPG]).

Question 19

Which of the following levels of PO₂ is associated with a significant oxygen content gain?

Accepted Answer

The oxygen-hemoglobin equilibrium curve is quite steep in the 40-60 mm Hg range, whereas it is almost flat above 100 mm Hg. A PO₂ change from 40 to 60 mm Hg represents a 15% hemoglobin saturation or oxygen content gain (from 75% to 90%). A change in PO₂ from 100 to 600 mm Hg represents an oxygen saturation and content gain of only 2.5% (from 97.5% to 100%). The additional dissolved oxygen generated by a PO₂ change from 100 to 600 mm Hg is only 1.5 mL/dL (500 mm Hg x 0.003), not enough to outweigh the oxygen content gain accompanying a 40 to 60 mm Hg PO₂ change.

Question 20

Which of the following is the conventionally accepted value for hemoglobin's oxygen-carrying capacity?

Accepted Answer

When hemoglobin is 100% saturated with oxygen, each gram of hemoglobin carries 1.34 mL of oxygen.

Quiz 8: Oxygen Equilibrium and Transport