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HEMATOLOGY > 5.1 HEMOGLOBIN PART 2 > Flashcards

5.1 HEMOGLOBIN PART 2 Flashcards

1
Q

What happens to hemoglobin in the lungs, where there is high O2 tension?

A

Hb binds O2 and transports it to tissues, where it releases O2 at low O2 tension.

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2
Q

What is P50 in relation to hemoglobin’s affinity for oxygen?

A

The partial pressure of O2 needed to saturate 50% of Hb, with a normal P50 value of 27 mmHg.

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3
Q

What does a rightward shift in the oxygen dissociation curve represent?

A

P50 > 27 mmHg, meaning lower Hb affinity for O2.

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4
Q

What are the two forms of hemoglobin in terms of oxygen affinity?

A

Relaxed (R) state: high O2 affinity | Tensed (T) state: low O2 affinity.

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5
Q

What are the forms of hemoglobin when oxygenated and deoxygenated?

A

Oxyhemoglobin (oxygenated) | Deoxyhemoglobin (deoxygenated).

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6
Q

What process describes CO2 diffusion into RBCs and its conversion to carbonic acid?

A

CO2 diffuses into RBCs, combines with water to form H2CO3, which dissociates into H+ and HCO3-.

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7
Q

What is the Bohr effect in CO2 transport?

A

H+ binds to HbO2, causing O2 to diffuse out of RBCs, shifting the oxygen dissociation curve to the right.

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8
Q

What is the chloride shift in CO2 transport?

A

As HCO3- diffuses out of RBCs, Cl- diffuses into the cell to maintain electrical neutrality.

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9
Q

What percentage of CO2 is carried to the lungs as plasma bicarbonate (HCO3-)?

A

70% of CO2 is carried to the lungs as plasma bicarbonate.

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10
Q

What percentage of CO2 binds with globin chains to form carbaminohemoglobin?

A

5% of CO2 binds with globin chains in nonoxygenated Hb.

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11
Q

How does nitric oxide regulate blood flow in relation to hemoglobin?

A

Nitric oxide binds to hemoglobin at high O2 tension (vasoconstriction) and is released at low O2 tension (vasodilation).

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12
Q

Dysfunctional hemoglobins unable to transport O2

A

dyshemoglobins

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13
Q

What percentage of dyshemoglobinemia cases are acquired vs. hereditary?

A

Majority are acquired; a small percentage are hereditary.

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14
Q

Hemoglobin bound to carbon monoxide (CO), normally less than 2% of total hemoglobin

A

carboxyhemoglobin (COHb)

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15
Q

Why is carbon monoxide considered a “silent killer”?

A

It is odorless and colorless, making it difficult to detect.

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16
Q

Name some sources of exogenous carbon monoxide (CO).

A

Gasoline motors, gas heaters, tobacco smoking, defective stoves, and industrial wastes.

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17
Q

What is the affinity of carbon monoxide (CO) for hemoglobin compared to oxygen (O2)?

A

240 times greater than O2, causing a leftward shift in the oxygen dissociation curve.

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18
Q

What are the symptoms of carboxyhemoglobinemia at 20%-30% COHb levels?

A

Dizziness, nausea, muscular weakness, headache, vomiting, confusion.

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19
Q

At what level of COHb do severe symptoms like asphyxiation, coma, or death occur?

A

50%-70% COHb

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20
Q

What is the typical COHb percentage in nonsmokers and smokers?

A

0.5% in nonsmokers, 5% in smokers.

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21
Q

How is COHb quantitatively measured in the lab?

A

Using spectrophotometry (540 nm) or gas chromatography.

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22
Q

What is the first step in treating CO poisoning?

A

Removal of the source of carbon monoxide.

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23
Q

What treatments are used for severe carbon monoxide poisoning?

A

High levels of O2 and hyperbaric O2 therapy.

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24
Q

At what COHb level is carbon monoxide poisoning diagnosed in nonsmokers and smokers?

A

> 3% in nonsmokers, >10% in smokers.

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25
Q

Hemoglobin where heme iron is oxidized to Fe3+, normally comprising 1% of total hemoglobin.

A

methemoglobin (MetHb)

26
Q

Name the enzymes and substances that reduce methemoglobin (MetHb) in the body

A

NADH-cytochrome-b5 reductase,
ascorbic acid,
reduced glutathione, and
NADPH-methemoglobin reductase.

27
Q

A disorder characterized by increased levels of MetHb due to increased production or decreased activity of NADH-cytochrome-b5 reductase.

A

methemoglobinemia

28
Q

What causes toxic methemoglobinemia (acquired form)?

A

Exposure to exogenous oxidants such as nitrites, nitrates, benzocaine, aniline dyes, and drugs of abuse.

29
Q

What is the pathophysiology of toxic methemoglobinemia?

A

Exogenous oxidants oxidize heme iron to Fe3+, impairing oxygen binding, leading to cyanosis and hypoxia due to a leftward shift in the oxygen dissociation curve.

30
Q

How is toxic methemoglobinemia treated based on MetHb levels?

A

<30% MetHb: Removal of offending oxidant.
≥30% MetHb: Intravenous infusion of methylene blue (methylthioninium chloride).

31
Q

Mutations in the gene coding for NADH-cytochrome b5 reductase, leading to diaphorase deficiency and increased MetHb.

A

hereditary methemoglobinemia

32
Q

What are the characteristics of homozygotes with hereditary methemoglobinemia?

A

Homozygotes have <50% MetHb, are cyanotic, and experience mild hypoxia.

33
Q

How do heterozygotes with hereditary methemoglobinemia react to oxidizing chemicals or drugs?

A

They may become cyanotic and hypoxic when exposed to these substances.

34
Q

What therapies can reduce MetHb levels in hereditary methemoglobinemia?

A

Ascorbic acid and methylene blue.

35
Q

What causes inherited hemoglobin M (Hb M) methemoglobinemia?

A

Mutations in the α, β, or γ globin genes, leading to abnormal polypeptide chains that favor iron oxidation to Fe3+.

36
Q

How do patients with hemoglobin M methemoglobinemia (Hb M Disease) present clinically?

A

They have asymptomatic cyanosis and do not respond to methylene blue treatment.

37
Q

What diagnostic methods are used to identify Hb M variants?

A

Hemoglobin electrophoresis, HPLC, and DNA mutation testing.

38
Q

What color does blood appear in individuals with increased MetHb levels?

A

Chocolate brown

39
Q

How are MetHb levels quantified in the laboratory?

A

Using spectrophotometry at 630 nm-635 nm.

40
Q

What are the clinical symptoms at different MetHb levels?

A

<25%: Asymptomatic.

30%: Cyanosis and hypoxia.

50%: Coma and death.

41
Q

How can exposure to carbon monoxide occur?

A

Exposure may be coincidental, accidental, or intentional (suicidal).

42
Q

What happens to hemoglobin when CO binds, even at very low concentrations of CO in the air?

A

CO can bind to hemoglobin even if its concentration in the air is extremely low (e.g., 0.02%-0.04%).

43
Q

What are the symptoms and physical findings associated with increasing levels of COHb in terms of color of blood?

A

Cherry red color of blood, turning the skin bright cherry red (reversible).

44
Q

What are the COHb levels associated with exposure to carbon monoxide in the air?
A:

A

0.04% CO in air → 10% COHb (shortness of breath on exertion, impairing judgment with long exposure).
0.1% CO in air → 50%-70% COHb.
0.4% CO in air → 80% COHb.

45
Q

Irreversibly oxidized and partially denatured hemoglobin due to sulfur binding

A

sulfhemoglobin (SHb)

46
Q

What disorder is associated with sulfhemoglobin?

A

Sulfhemoglobinemia

47
Q

What is the pathophysiology of sulfhemoglobinemia?

A

Exposure to sulfur chemicals or drugs leads to the incorporation of a sulfur atom into the pyrrole ring of heme, resulting in a green hemochrome.

48
Q

Chemicals or drugs that may cause sulfhemoglobin

A

sulfonamides, phenacetin, nitrites, phenylhydrazine

49
Q

How does sulfhemoglobin affect oxygen binding?

A

Affected heme subunits are unable to bind O2, and unaffected heme subunits have a decreased affinity for O2, causing a rightward shift in the oxygen dissociation curve, leading to cyanosis.

50
Q

What color does increased sulfhemoglobin give to blood?

A

Mauve-lavender color.

51
Q

What is formed when sulfhemoglobin combines with carbon monoxide?

A

Carboxysulfhemoglobin.

52
Q

In which conditions has sulfhemoglobin been reported?

A

Severe constipation, bacteremia due to Clostridium perfringens, and enterogenous cyanosis.

53
Q

How is sulfhemoglobin detected?

A

It cannot be detected by the cyanmethemoglobin method; its absorbance peak is between 600 nm and 620 nm.

54
Q

What effect does a shift to the left have on hemoglobin’s affinity for oxygen?

A

Increased affinity for oxygen

55
Q

What effect does a shift to the right have on hemoglobin’s affinity for oxygen?

A

Decreased affinity for oxygen.

56
Q

How does pH affect hemoglobin’s affinity for oxygen?

A

Shift to the Left: Increased pH (alkaline/low H⁺)
Shift to the Right: Decreased pH (acidic/high H⁺)

57
Q

How does 2,3-BPG affect hemoglobin’s state?

A

Shift to the Left: Decreased levels of 2,3-BPG (relaxed form)

Shift to the Right: Increased levels of 2,3-BPG (tense form)

58
Q

How does carbon dioxide (CO2) affect hemoglobin’s affinity for oxygen?

A

Shift to the Left: Decreased CO2
Shift to the Right: Increased CO2

59
Q

What effect does body temperature have on hemoglobin’s affinity for oxygen?

A

Shift to the Left: Decreased temperature

Shift to the Right: Increased temperature (O2 will cool off the body)

60
Q

What are other causes that can shift the oxygen dissociation curve to the left?

A

Alkalosis,

multiple transfusions of stored blood with depleted 2,3-BPG,

Hb F (p50 = 19-21 mmHg/weak binding to 2,3-BPG leading to increased Hb affinity for O2).

61
Q

What are other causes that can shift the oxygen dissociation curve to the right?

A

Acidosis,
high altitude,
pulmonary insufficiency,
congestive heart failure (CHF),
severe anemia.

HEMATOLOGY (10 decks)

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