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Respiratory - Anatomy and Physiology > Hemoglobin > Flashcards

Hemoglobin Flashcards

1
Q

What is hemoglobin composed of?

A

4 polypeptide subunits: 2 alpha and 2 beta.

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2
Q

What two forms does hemoglobin exist in?

A

1) T (taut, deoxygenated) form has a low affinity of oxygen.

2) R (relaxed, oxygenated) form has a high affinity for oxygen (300x higher)

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3
Q

What does it mean to say Hb exhibits positive cooperativity?

A

When substrate (oxygen) binds to the active site, that in turn activates the other subunits and increases their affinity for oxygen. (with each oxygen, hemoglobin wants more oxygen).

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4
Q

What does it mean to say that Hb exhibits negative allostery?

A

With each oxygen that dissociates, a negative allosteric modulator binds to another site (not the active site) on the hemoglobin molecule, decreasing affinity for oxygen and encouraging dissociation of other oxygen molecules.

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5
Q

What is the effect of 2,3-BPG on hemoglobin’s affinity for oxygen?

A

It decreases oxygen affinity, favors taut form –> favors oxygen unloading.

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6
Q

What favors oxygen unloading?

A

CO2+, H+, Cl-, and 2-3BPG and temperature.

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7
Q

What are the subunits of fetal hemoglobin?

A

2a and 2gamma.

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8
Q

How does fetal hemoglobin’s affinity for 23BPG differ from adult Hb, and why?

A

Fetal hb has LOWER affinity for 23BPG than adult. Thus, it has a higher affinity for oxygen, so that it can favor taking oxygen from maternal blood.

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9
Q

What is the normal state of iron in Hb?

A

Fe2+ (to bind O2).

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10
Q

What is it called when iron in Hb is oxidized?

A

Fe3+ is called methemoglobin.

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11
Q

How does Fe3+ change Hb’s affinity for oxygen? What does its increase Hb’s affinity for?

A

Decreases oxygen, but increases affinity for cyanide.

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12
Q

How does metheoglobinemia present?

A

Cyanosis with chocolate colored blood.

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13
Q

What can cause methemoglobinemia?

A

Nitrites and benzocaine –> oxidize Fe2+ to Fe3+.

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14
Q

How is methemoglobinemia treated?

A

Methylene blue. (methylene blue gets quickly reduced, and then is able to reduce Fe3+ back to fe2+)

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15
Q

In what scenario may induced methemoglobinemia be used as a treatment?

A

Cyanide poisoning.

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16
Q

What is the treatment for cyanide poisoning?

A

1) Nitrites - get cyanide off the cytochromes and onto the induced methemoglobin
2) Thiosulfate - a substrate in the metabolism of cyanide
3) treat the methemoglobinemia with methylene blue

17
Q

What is Hb bound to CO in place of O2 called?

A

Carboxyhemoglobin

18
Q

How does binding capacity of CO compare to O2?

A

Binds competitively and with 200x greater affinity

19
Q

What does carboyxhemoglobinemia cause?

A

Causes decrease in oxygen-bnding capacity of hemoglobin, and left shift in oxygen-hemoglobin dissociation curve (decrease oxygen unloading in tissues).

20
Q

How is carboyxhemoglobinemia treated?

A

100% oxygen and hyperbaric O2.

21
Q

Why does the oxygen dissociation curve have a sigmoidal shape?

A

Do to positive cooperativity; tetrameric Hb has greater affinity for each subsequent O2 bound.

22
Q

Why does myoglobin not show sigmoidal oxygen dissociation curve?

A

It is monomeric and thus does not show positive cooperativity.

23
Q

What is on the X axis of the oxygen dissociation curve? What do the two ends of the axis represent?

A

PO2. The far right (close to 100) represents fully oxygenated blood leaving the lungs. The left represents blood leaving the tissues that has dropped off oxygen.

24
Q

What does a shift to the right of the oxygen dissociation curve represent?

A

Lowers the Hb saturation at a given PO2; represents unloading of O2 to the tissue.

25
Q

What factors shift the oxygen dissociation curve to the right?

A

States when tissue needs oxygen!

H+, CO2, Exercise, 2,3BPG, Altitude, and Temperature.

26
Q

Where is the fetal oxygen dissociation curve relative to adult?

A

To the left; has a higher affinity for oxygen (less willing to drop it off, so easier for it to pick it up from maternal blood).

27
Q

What is the formula for oxygen content of the blood?

A

(Oxygen binding capacity * % saturation) + dissolved O2

28
Q

What is the normal binding capacity of Hb for O2?

A

1.34 mL O2

29
Q

What is the normal Hb amount in the blood?

A

15 g/dL

30
Q

What is the cutoff for cyanosis?

A

Deoxygenated Hb > 5g/dL

31
Q

What is the normal O2 binding capacity in the blood?

A

Binding capacity of Hb for oxygen * amount of Hb = 20.1mlO2/dL

32
Q

With decrease in hemoglobin, which parameters stay the same and which change?

A

Total O2 content of blood drops.
Hemoglobin drops.
%O2 sat of hemoglobin stays the same.
Dissolved O2 (PaO2) stays the same.

33
Q

What parameters change with CO poisoning?

A

Hb = normal
%O2 sat of Hb decreases.
Total oxygen content decreases.
Dissolved PaO2 = same.

Respiratory - Anatomy and Physiology (5 decks)

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