04A Hemoglobin

7/28/2019 04A Hemoglobin

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Hemoglobin

Heme = Fe++ + Porphyrin Ring

+

Globin


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Hemoglobin

Function Conjugated protein

for transport of O2 &

CO2

&

Buffer (O2

Dissociation Curve)


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Basic Structure

How many? subunits:

How many? iron-containing tetrapyrroleheme rings

How many? polypeptide

globin chains ? identical alpha chains

? identical non-alphachains


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Basic Structure

Each chain arrangedin -helix w/ 8individual helicalsegments (labeled A -H)

Each globin moleculehas both hydrophobic& hydrophilic areas


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Basic Structure

Fe-containing heme ring w/inhydrophobic region of globin -Heme Pocket

Hydrophobic nature protectsFe residue from oxidation

Each Fe at center of hemeresidue held in place & kept

active (Fe++) by 2 histidineresidues


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Hemoglobin Chemistry

O2 binds to heme (Iron)

97% carried this way

CO2 binds to globin

20% bound

80% free in plasma

CO2 causes acidity in

plasma, effects the pH

balance of the blood

Blood can carry both at

one time different

binding


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Basic Structure

Each globin (141 aa)

All non- chains (146

aa) W/ considerable

structural homology

among non-alpha

chains

Full saturation: 1 gm

Hgb holds 1.34 mL of

O2


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Normal Hgb:

Hgb A1

95 - 98% (adult)

15 - 40% at birth

predominates at 6 12mons

Hgb F

< 2% (adult)

1 - 0.8% (3 y/o)


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Hgb derivatives (Heme changes)

Oxyhgb (bright red) vs Reduced hgb (purple red)

Maintained by methemoglobin- cytochrom C

reductase 575 nm


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Carboxyhgb (cherry

pink)

200 X affinity vs O2 Collect in citrate

Test: ammonia + blood

(25% COHgb)

CO poisoning occur atlevels of 20-30%

540 nm


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Heavy smokers: Smokers: 1-10%


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Methgb (0.5% normal in

blood)

Fe++ Fe+++ brown

No O2 binding cyanotic

Induced by oxidizing

agents (nitrates, nitrites,

quinones, chlorates)

G-6-PD deficiency

525 nm

Sulfhgb (0- 2.2% normal

in blood)

Sulfa drugs (sulfonamides);

aromatic aminestrinitrotoluene

Irreversible binding RES

Myoglobins

Porphyrins


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Iron Metabolism


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Body Iron Distribution and StorageDietary iron

Utilization Utilization

Duodenum

(average, 1 - 2 mg

per day)

Muscle

(myoglobin)

(300 mg)

Liver

(1,000 mg)

Bone

marrow

(300 mg)Circulating

erythrocytes

(hemoglobin)

(1,800 mg)

Reticuloendothelial

macrophages

(600 mg)

Sloughed mucosal cellsDesquamation/Menstruation

Other blood loss(average, 1 - 2 mg per day)

Storage

iron

Plasma

transferrin

(3 mg)

Iron loss


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Major Iron Compartments

Metabolic:

Hgb 1800 - 2500 mg

Myoglobin 300 - 500 mg

Storage:

Iron storage 0 - 1000 mg

Transit:

Serum iron 3 mg

Total 3000 - 4000 mg


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Red cell indices

Hemoglobin (gm\dl): 13.5- 17 M

12- 15 F

Hematocrit (Vol%): Volume of RBCs /Total blood

39- 49 % M

33- 43% F

RBCs ct (106/ul): 4.3- 5.9 M3.5- 5 F


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Iron Deficiency

Anemia (IDA)


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Clinical

Features: General features of

Anemia

Pallor, Weakness,Lethargy

Breathlessness onexertion

Palpitationsheart failurepedal edema


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Clinical

Features: Special features in

IDA:

Angular cheilitis,atrophic glossitis,

Esophagealatrophy/web

dysphagia,Koilonychia, brittle

nails, gastricatrophy


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PBS: Response to Iron Tx

Dimorphic blood film


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Other LAB Tests:

DEC SERUM Fe

DEC SERUM FERRITIN Most useful, cost effective test of Fe stores

> 100 ng/ml r/o IDA Except in acute hepatitis or liver necrosis butnot chronic liver dse (elevated- release of Fe stores)

Falsely elevated- disseminated TB & Hodgkin's disease

INC TIBC (high specificity- near 100% but poorsensitivity- < 30%)

BM: ASYNCHRONOUS RBC-POIESIS


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Hemochromatosis: Overview

Def: Xss accumulation of Fe w/ organ damage

Iron arithmetic: Normal total body pool: 2-5 gm

Hgb (2 gm)

Storage: ferritin & hemosiderin (0.5 - 1 gm)

Myoglobin (0.3 gm)

Normal liver storage: 0.5 gm

Hemochromatosis: Total body Fe > 50 gm

At least 1/3 is stored in liver


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Hemochromatosis: classification

Genetic (hereditary) vs secondary (acquired)

Secondary causes iron overload: Parenteral iron overload (transfusions, iron-dextran

injections)

Ineffective erythropoiesis hemolytic anemias (mostcommon secondary cause)

Increased oral intake (Bantu siderosis)Congenital atransferrinemia

Chronic liver disease (mostly alcoholic)


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Genetic Hemochromatosis

Homozygous recessive

HFE gene on chr 6p (near HLA gene locus)

MC mutation in HFE: tyrosine substituted forcysteine at aa 282 (C282Y)

Gene frequency: 6% northern European whites;homozygosity 0.45% (1 in 220)

M: F = 6:1

Males show disease earlier (no menses)


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Hereditary Hemochromatosis:

pathogenesis


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Genetic Hemochromatosis:

Pathology Deposition hemosiderin

in multiple organs (browngranules of aggregatedferritin):

Liver & pancreas (mostsevere)

Myocardium

Pituitary, adrenal, thyroid,parathyroid glands

Joints (synovitis) and skin

Testes (atrophy)


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Hemochromatosis

Genetic dse

Excess amounts of

iron Arthritis, cirrhosis,

DM, heart failure,

HCC


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Hemochromatosis: Clinical Dx

Signs:Abdominal pain

Hepatomegaly

Skin pigmentation(brown-gray)

DM

Cardiac dysfunction

Arthritis

Hypogonadism


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Hemochromatosis: Clinical Dx

Diagnostic tools:

Markedly elevated serum ferritin (best screening test)

HFE gene molecular analysis Liver biopsy w/ quantitative Fe analysis

Normal: < 1,000 ug Fe/gm

Hemochromatosis: > 10,000 ug Fe/gm

Evaluate for secondary causes (vs. genetic)


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Anemia of Chronic

Disease: ACD


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ACD - ETIOLOGY: ANY

CHRONIC DSE Inflammatory:

Temporal arteritis

(may be a presenting

sign)

Rheumatoid arthritis

Cancer

Non-inflammatory:

CHF

COPD DM


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ACD

Infections: TB, SBE, Osteomyelitis

Chronic UTI or PN

Fungal

Malignancy: Mets

Leukemia

Lymphoma

Myeloma

Chronic inflammatorydisorders: RA

SLE Sarcoid

Collagen Vascular Dse

Polymyalgia Rheumatica

Chronic Hepatitis

Decubitus ulcer


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ACDDefect

Storage Iron

IL-1TNF IFN

Erythroid Precursors

(dec responsiveness to EPO)

BM Storage

Iron (Blue)

Fe SEQUESTRATION IN BM HISTIOCYTES

w/ defective Fe utilization & shorten RBC survival


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ACD - LAB DX:

INC. ESR

INC. HAPTOGLOBIN

Dec serum Fe

Dec TIBC

BM: Inc BM Fe stores w/ dec sideroblasts


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IDANormal

ACD


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Sample question #1

ACD is due to inadequate production of, orpoor response to, which one of the

following?

A. Iron

B. FolateC. Erythropoietin

D. Ferritin

E. HemosiderinAFP, Nov. 15, 2000


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Heme Synthesis


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Porphyrin Synthesis

& Structure


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Heme Synthesis

Glycine & Succinyl Co-A-amino

levulinic acid (-ALA)

The rate-limiting step in heme synthesis-intra-mitochondrial ALA- synthase

-ALA travels to cytoplasm; converted toPBG, a monopyrrole


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Heme Synthesis

PBG (monopyrrole) Protoporphyrin IX

(biologically active tetrapyrrole)

Fe inserted into tetrapyrrole ring in mitochondria

Heme synthesis:

Stimulated by Fe

Repressed when Fe is inadequate (IDA)


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Sideroblastic

Anemia


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SIDEROBLASTIC A. -

MECHANISM: Defective prdn of heme under- hgb

erythroid precursors w/ microcytosis

REFRACTORY A. (RESISTANT TO TX) INEFFECTIVE ERYTHROPOIESIS

(ANEMIA W/ HYPERPLASTIC BM)


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SIDEROBLASTIC A - ETIOLOGY

& Mechanism: HEREDITARY (X LINKED/ AR)

HEPATOSPLEENOMEGALY;THROMBOEMBOLISM


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& Mechanism:ACQUIRED:

IDIOPATHIC

NEUTROPENIA W/ PELGER HUET CELLS

PRONE TO Fe OVERLOAD; TE

10% DEVELOP AML


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& Mechanism: ACQUIRED:

DRUG INDUCEDALCOHOL- FOLATE DEF. + MALNUtrition

INH- VIT. B6 METABOLISMCHLORAMPHENICOL- MITOCHONDRIAL

INHIBITION

LEAD- HEME PATHWAY

Zinc, cycloserine, plavix

DISEASE ASSO. (THYROID; CA; LYMPHOMA;MM; RA)


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Sideroblastic A Lab Dx:

PBS: Papenheimer

Bodies; Basophilic

stippling in Pb

poisoning; Dimorphic(macrocytic + intensely

microcytic RBCs) in

patient w/ acquired

sideroblastic a;anisopoikilocytosis;

Target cells


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Sideroblastic A Lab Dx:

Serum Fe: Inc

Stigmata of a myelodysplastic syndrome

BM: Ringed sideroblasts on BM Fe stain;inc hemosiderin


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Porphyria cutanea tarda

Etiology:

Uroporphyrinogen decarboxylase def

Anti HC Ab

S/S:

Cutaneous photosensitivity


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Porphyria cutanea tarda

Features:

Portal inflam w/

cirrhosis

HCC

Inc hepatic Fe

Inc urinary

uroporphyrin

Lab tests:

Inc urine uroporphyrin

Inc aminotransferase


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Acute intermittent porphyria

AD w/ incomplete penetrance (other familymembers w/ the condition maybeasymptomatic)

Drugs & alcohol induced (P450 enzymeinducers)

Acute attack: urine turns dark on standing

(high ALA & PBG levels). Levels remainmoderately raised between attacks


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Variegate porphyria

AD disorder

Features: Cutaneous fragility &

photosensitivityAcute neurological attacks common


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Globin Synthesis


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Location of the Globin Genes

Duplication of genes

for:

Globin

Globin (G & A) *

G & A differ from

one another only at

position 136 (glycine

& alanine

respectively)


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Globin chain synthesis


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Globin chain synthesis cluster - chromosome 16

b cluster - chromosome 11

z2e2 Gower 1

z22 Portland Embryonic

2e2 Gower II

22 F Fetal 95%

12

e G bA


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Ferritin


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Iron deficiency

Reduced

HB electrophoresis Anemia of Chronic Disease

Normal

Bone marrow

Ringed sideroblasts

Increased

Furtherinvestigations to

find the cause are

necessary

If HB

electrophoresis isnormal then do

alpha gene mapping

HypochromiaMicrocytic

Note: Anisocyosis:

RDW

poikilocytes


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WAKAS!!!

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04A Hemoglobin