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CardioPulmRenal Final > Erythrocyte Biochemistry (Pt 1) > Flashcards

Erythrocyte Biochemistry (Pt 1) Flashcards

1
Q

What are the four chains in adult hemoglobin (Hb)?

A

2 alpha

2 beta

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2
Q

In heme, what state is the iron in?

A

ferrous (2+)

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3
Q

Where is the iron atom in heme?

A

center

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4
Q

What is the purpose of heme?

A

carries oxygen

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5
Q

Is heme hydrophilic or hydrophobic?

A

hydrophobic

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6
Q

What comprises the main framework of heme?

A

a porphyrin ring

4 pyrroles

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7
Q

What happens to the iron molecule when oxygen binds to the heme?

A
  • originally it lies outside the plane of the porphyrin ring
  • iron moves into the plane when oxygen binds
  • proximal His is pulled
  • changes interaction w/ associated globin chains
  • distal His stabilizes the oxygen
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8
Q

What happens to the hemoglobin as it enters tissues with low pH (actively respiring tissues)?

A

-as pH decreases, the binding affinity of Hb for oxygen decreases

  • His picks up a H+ ion
  • Hb changes conformation and releases oxygen
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9
Q

Between what pressures is the steepest portion of the oxygen-dissociation curve?

A

20-40 torr

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10
Q

What are the subunits of embryonic hemoglobin?

A

Gower 1: 2 zeta, 2 epsilon
Gower 2: 2 alpha, 2 epsilon
Portland: 2 zeta, 2 gamma

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11
Q

What are the subunits of fetal hemoglobin (HbF)?

A

2 alpha

2 gamma

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12
Q

Which has higher oxygen affinity, fetal Hb or maternal Hb?

A

fetal hemoglobin

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13
Q

Why does fetal hemoglobin have a higher affinity for oxygen?

A

it doesn’t bind well to 2,3-BPG

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14
Q

What hemoglobin is present in sickle cell disease?

A

Hb S

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15
Q

What makes Hb S different than normal adult hemoglobin?

A

a mutation in the beta globin chain

-glutamic acid (in the 6th position) is switched to valine
negative charged aa to a hydrophobic aa

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16
Q

After ferrous iron (Fe2+) is absorbed into the enterocyte, what enzyme converts it to ferric form?

A

ferroxidase

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17
Q

How is iron stored in the liver?

A

as ferritin and homosiderin

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18
Q

Since plant-based ferric iron is not easily absorbed, how does it get into the enterocyte?

A

it’s converted to ferrous form by ferric reductase

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19
Q

What cofactor is needed by ferric reductase?

A

vitamin C

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20
Q

What transporter does ferric iron use to enter the enterocyte

A

after being converted to the ferrous form, the iron enters the enterocyte via DMT-1

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21
Q

How is iron exported out of the enterocyte?

A

ferroportin

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22
Q

How does iron get transported through the blood to its target tissues?

A

it’s bound to transferrin

23
Q

Once at the target tissue, how does iron get into the cells?

A

transferrin binds to transferrin receptors (TfR) and it is endocytosed by clathrin-coated pits

24
Q

Once in the endosomes, how is the iron released from the transferrin?

A
  • the low pH (5.5) of the endosomes causes transferrin to be released from its receptor
  • endosome docks onto mitochondria and transfers Fe3+ in via DMT-1
25
Q

What process is the main regulator of iron in the body?

A

absorption

26
Q

What hormone regulates iron absorption?

A

hepcidin

27
Q

Where is hepcidin synthesized?

A

liver

28
Q

What controls the level of hepcidin?

A

human homeostatic iron regulator protein

HFE

29
Q

What is hepcidin’s mechanism of action?

A

binds to ferroportin and causes it to be internalized and degraded by lysosomes

30
Q

Will high levels of iron increase or decrease the amt of hepcidin?

A

increase

31
Q

What are some causes of iron deficiency?

A
  • insufficient dietary iron
  • insufficient absorption of iron
  • heavy menstruation
  • GI bleed or ulcers
  • aspirin overuse
32
Q

What type of anemia might an iron deficiency cause?

A

hypochromic microcytic anemia

33
Q

What genetic disease might be responsible for an iron overload?

A

Hereditary Hemochromatosis

34
Q

What are the characteristics of hereditary hemochromatosis?

A
  • iron accumulates in the liver, heart, and pancreas
  • causes cirrhosis, diabetes, arthritis, heart failure
  • autosomal recessive gene

-defective HFE (human homeostatic iron regulator protein) which normally controls hepcidin levels

35
Q

What are the total body iron levels like in a pt. with hereditary hemochromatosis vs. a normal person?

A

15g

3-5 g normal

36
Q

What type of anemia do deficiencies in B9 (folate) and/or B12 (cobalamin) cause?

A

megaloblastic anemia

37
Q

What are the characteristics of megaloblastic anemia from B12 and B9 deficiencies?

A
  • diminished DNA synthesis in bone marrow
  • cell volume > 100 fL (normal 80-100)
  • macrocytic, but normochromic
  • hypersegmented neutrophils
38
Q

What is the general structure of folate?

A
  • pteridine (N-containing ring)
  • PABA ring (p-amino benzoic acid)
  • glutamate residues (lots of them)
39
Q

What is the active form of folate?

A

tetrahydrofolate (THF)

40
Q

What enzyme gets folate into the active form?

A

dihydrofolate reductase (DHF reductase)

acts on it 2x

41
Q

In regards to DNA synthesis, why is THF important?

A

-it is used in the synthesis of purines and in the synthesis of thymine

42
Q

What drug inhibits dihydrofolate reductase (DHF reductase)?

A

methotrexate

43
Q

In what part of the body is B9 absorbed?

A

jejunum in the small intestines

44
Q

How much folate is normally stored in the body?

A

5-10 g

3-6 months worth

45
Q

What level constitutes a folate deficiency?

A

< 3 ng/mL

46
Q

What is the primary form of folate circulating in the bloodstream?

A

N5-methyl-THF

47
Q

What is folate’s main duty in biochemical reactions?

A

transfer of one-carbon groups

48
Q

When B9 accepts a carbon group from serine, what reaction happens?

A
  • B9 becomes N5, N10-methylene THF
  • it donates a carbon and becomes DHF
  • DHF reductase comes back in
  • regenerates THF
49
Q

When B9 accepts a carbon group from glycine, what reaction happens?

A
  • B9 becomes N5,N10-methylene THF
  • then becomes N5-methyl THF
  • then B12 removes the methyl group
  • becomes the active form of THF
50
Q

What is usually the main cause of a B12 deficiency?

A

lack of intrinsic factor

51
Q

Delineate the process of B12 absorption.

A
  • binds to R binder proteins in the stomach
  • R binders are degraded by pancreatic proteases
  • binds to intrinsic factor
  • sent into the bloodstream
  • carried by transcobalamin III
52
Q

What does the Schilling Test screen for?

A 
pernicious anemia
(lack of intrinsic factor)
53
Q

How does the first part of the Schilling Test work?

A
  • ingest labeled B12
  • saturate liver with regular B12 so labeled isn’t stored

-check urine for labeled B12 indicating that it’s been absorbed out of the GI tract

54
Q

How does the second part of the Schilling Test work?

A
  • if labeled B12 is not found in the urine, administer the labeled B12 again, but with intrinsic factor this time
  • check urine for labeled B12

CardioPulmRenal Final (13 decks)

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