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Human Physiology > Respiratory System: Gas Transport > Flashcards

Respiratory System: Gas Transport Flashcards

1
Q

How much of the oxygen in the blood is dissolved?

A

less than 2%

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2
Q

T/F. The solubility of oxygen in the water is low.

A

True, O2 is relatively insoluble in water (2mmol; ~40mg or 3ml/L). Only 3 mL can be dissolved in 1L of blood at the normal arterial PO2 of 100mmHg

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3
Q

___ O2 represents what is available to diffuse.

A

Dissolved

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4
Q

Resting O2 consumption is ~___ml/min, and the amount of dissolved O2 in the blood is less than ___% of what is needed to support basal metabolism.

A

250; 10

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5
Q

Because the dissolved O2 is not enough to support basal metabolism, what do we rely on for O2?

A

the O2 bound to hemoglobin (~98% of the total O2 in the blood)

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6
Q

What is the predominate protein in erythrocytes?

A

Hemoglobin

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7
Q

How many Hb molecules are there per cell?

A

250-280 million

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8
Q

Hb is a ___ molecule containing 4 protein subunits of ___, each with a ___ group that includes ___ iron atom that can ___ bind O2.

A

tetrameric; globin; heme; 1; reversibly

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9
Q

What is the maximum amount of O2 a molecule of Hb carries?

A

4 O2

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10
Q

Describe the carrying capacity or saturation of Hb.

A

it is reached with maximum HbO2 (oxyhemoglobin)

% saturation = % of Hb in HbO2

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11
Q

What is the total O2 in the blood a function of?

A

PO2 and amount of Hb in the blood

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12
Q

T/F. The binding of O2 to Hb changes the conformation of the Hb and oxygen molecule.

A

False, The binding of O2 to Hb changes the conformation of the Hb molecule BUT NOT the oxygen molecule.

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13
Q

Hb exhibits ___ binding of O2. The oxygen-Hb dissociation curve describes the effect of ___ on Hb ___.

A

cooperative; PO2; saturation

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14
Q

What are the two possible y axes on a O2-Hb dissociation curve?

A
  1. % saturation - proportion of Hb with O2

2. O2 content - total O2 per ml of blood

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15
Q

T/F. The binding of one oxygen molecule to deoxyhemoglobin increases the affinity of the remaining sites on the same hemoglobin molecule, and so on.

A

True.

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16
Q

The curve has a steep slope between ___ and ___ mmHg PO2 and a plateau between ___ and ___ mmHg PO2.

A

10; 60; 70; 100

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17
Q

T/F. The extent to which oxygen combines with hemoglobin increases very rapidly as the PO2 increases from 10 to 60 mmHg and from this point on a further increase in PO2 produces only a small increase in O2 binding.

A

True.

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18
Q

In the plateau region or ___ phase, PO2 is typical of ___ blood and therefore, Hb should ___ O2.

A

loading; arterial; keep

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19
Q

In the steep region or ___ phase, PO2 is in ___ capillaries and therefore there is need to ___ O2.

A

unloading; venous; release

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20
Q

T/F. The P50 (~60 mmHg) is the PO2 at which 1/2 of Hb is saturated.

A

False, The P50 (~25 mmHg) is the PO2 at which 1/2 of Hb is saturated.

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21
Q

PO2 is a measure of ___ O2 and ONLY dissolved O2 can diffuse into ___. It is critical to maintain a pool of dissolved O2 to supply ___ demand.

A

dissolved; tissues; mitochondrial

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22
Q

O2 bound to Hb cannot diffuse. So, when is O2 released from Hb into the dissolved pool?

A

when PO2 fall as it does when O2 diffuses out of the blood into interstitial fluid

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23
Q

T/F. Hb increases the total oxygen at any PO2, but must release O2 if it is to be used by tissues.

A

True.

24
Q

Hb serves to ___ O2 so that it can be transferred or released to the dissolved pool of O2.

A

store

25
Q

How does Hb maintain the PO2 gradient from alveolar air to pulmonary blood?

A

O2 from alveolar air diffuses across the respiratory surface into the plasma then across the plasma membrane of erythrocytes in order to bind to Hb.

26
Q

Why does O2 dissociate from Hb and diffuse out of erythrocytes into the mitochondria?

A

Because the mitochondria of the cells all over the body are utilizing oxygen, the cellular PO2 is less than the PO2 of the surrounding interstitial fluid. Therefore, O2 is continuously diffusing into cells. This causes the interstitial fluid PO2 to always be less than the PO2 of the blood so the net diffusion of oxygen occurs from the plasma to interstitial fluid. Therefore, the PO2 in the plasma is lower than RBC so Hb dissociates O2 and it diffuses to mitochondria.

27
Q

An increase in Hb affinity, shift curve to ___ and Hb is saturated at a ___ PO2.

A

left; lower

28
Q

A decrease in Hb affinity for O2 will shift the curve to ___ and Hb is ___ saturated for a given PO2.

A

right; less

29
Q

T/F. Hb affinity is decreased by factors associated with metabolic activity causing the curve to shift right.

A

True.

30
Q

What factors are associated with increased metabolic activity?

A

increased temp due to production of heat
increased CO2 (Bohr effect)
increased H+ (or decreased pH)
increased 2,3 diphosphoglycerate (2,3-DPG)

31
Q

CO2 and H+ binds the ___ part of Hb causing an ___ effect.

A

globin; allosteric

32
Q

What is a product of glycolysis in erythrocytes that enhances offloading/dissociation of O2 by allosteric modulation?

A

2,3-DPG

33
Q

What are the normal values of Hb and O2 in the blood?

A

15 g Hb and 20ml of O2 / 100 ml blood

34
Q

What condition is defined as having fewer erythrocytes due to blood loss or reduced eruthropoiesis?

A

anemia

35
Q

In anemia there is less Hb per ml of blood. What are the consequences of this condition?

A

No change in arterial PO2 or Hb saturation

Total O2 content is reduced

36
Q

___ replaces O2 on Hb by competing from ___ binding sites on Hb to form ___.

A

CO; Fe; carboxyhemoglobin

37
Q

What is Hb affinity for CO compared to O2?

A

200-fold greater

38
Q

What does CO do to the O2-Hb dissociation curve?

A

Shift curve to the left, thus decreasing the unloading of oxygen by Hb in the tissues or increasing its affinity for oxygen.

39
Q

How is CO2 transported?

A
  1. dissolved (7%)
  2. bound to Hb (~23%)
  3. as HCO3- (70%)
40
Q

T/F. CO2 is less soluble in plasma than O2.

A

False, CO2 is more soluble in plasma than O2.

41
Q

CO2 binds to the ___ portion of Hb and forms ___.

A

globin; carbaminohemoglobin

42
Q

For a given PCO2, total CO2 varies depending on HbO. What happens when PCO2 is increased?

A

increase PCO2 = increase affinity of Hb for CO2. In venous blood, more CO2 on Hb than in arterial blood therefore, decrease PO2 = increase Hb affinity for CO2

43
Q

What happens to CO2 in water/plasma?

A

CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+

44
Q

What is the enzyme that catalyzes the formation of carbonic acid? Where is it found?

A

carbonic anhydrase (CA)

found in erythrocytes (not plasma)

45
Q

Erythrocytes have a ___ / ___ transporter that moves ___ into plasma as it forms. The CA reaction ___ the plasma.

A

HCO3-; Cl-; HCO3-; acidifies

46
Q

Explain how CO2 leaves the tissues and enters the RBC.

A

dissolved CO2 diffuses into the plasma then into RBC. Some binds Hb and some is converted to bicarbonate, which is transported into plasma

47
Q

Dissolved CO2 diffuses into alveoli and ___ PCO2 in the pulmonary capillaries. Hb unloads CO2 and loads ___. The carbonic acid reaction ___ which maintains CO2 ___ into alveolar air.

A

decreases; O2; reverses; gradient

48
Q

H+ binds to ___ residues on Hb but its affinity depends on ___.

A

histidine; PO2

49
Q

Why does deoxyHb have a high affinity for H+ and oxyHb have a low affinity for H+?

A

so deoxyHb can buffer most of the H+ and only a small amount of the H+ generated in the blood remains free. This explains why venous blood is slightly more acidic (pH = 7.36) than arterial blood (pH = 7.40).

50
Q

T/F. In the lung, Hb picks upi H+ and minimizes the effect of HCO3- on pH and in the tissues, Hb releases H+ to combine with HCO3- and CA reaction runs in reverse.

A

False, In the TISSUES, Hb picks upi H+ and minimizes the effect of HCO3- on pH and in the LUNGS, Hb releases H+ to combine with HCO3- and CA reaction runs in reverse.

51
Q

Hb buffers much of the H+ produced by the CA reaction. What is the pH in the arterial and venous blood?

A 
arterial = 7.40
venous = 7.36
52
Q

What term is used to describe increased arterial H+ concentration due to carbon dioxide retention?

A

respiratory acidosis

53
Q

In respiratory acidosis, the respiratory rate is ___ than normal or ___ results in increases in PCO2 and [H+].

A

lower; hypoventilation

54
Q

What is a patient doing in extreme hypoventilation?

A

breath-holding

55
Q

What happens when the respiratory rate is faster than normal or hyperventilation results in decreases in [H+] and PCO2?

A

Respiratory alkalosis

Human Physiology (22 decks)

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