263b sickle cell Flashcards Preview

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Flashcards in 263b sickle cell Deck (11):
1

hemoglobin - what globin chains are present in adults? what is in each chain?

HbA = a2,b2 (97%)
HbA2=a2d2 (3%)
HbF=a2g2 (increased with hydroxyurea)

heme = Fe + protoporphyrin: can bind O2, CO when reduced (Fe 2+)

2

where are the two globin gene?

a - chromosome 16

b - chromosome 11

arranged in order of globin production during life

3

hemoglobin switching

10 weeks: E (embryo) --> gama

birth-6 months: gamma --> B

4

SCD mutation?

HbS point mutation in B chain

G --> V single amino acid replacement at position 6.

5

SCD pathogenesis?

Pathogenesis: low O2, dehydration, or acidosis ->

sickling (deoxygenated HbS polymerizes) -->

anemia and vaso-occlusive disease.

6

SCD - newborn presentation? heterozygote advantage? AA carriers?

Newborns are initially asymptomatic (high HbF and low HbS)

Heterozygotes (sickle cell trait) have resistance to malaria (homozygous will kill you though --> example of balanced polymorphism)

8% of African Americans carry the HbS trait

7

Sickle cell - skull x-ray appearance?

“Crew cut” on skull x-ray due to marrow expansion from increased erythropoiesis (also in thalassemias).

8

SCD - treatment?

hydroxyurea (increases HbF)

bone marrow transplantation.

9

SCD - hydration of RBC?

dehydrated because increased K efflux and KCl- cotransport efflux --> efflux of H2O --> irreversible sickling

9

SCD - painful crisis presentation?

dactylitis (painful hand swelling)
acute chest syndrome (most common cause of death in adults)
avascular necrosis
stroke (5-10 years old)
severe back pain

acute chest syndrome = fever + abnormal CXR + respiratory syndrome

9

SCD - complications?

aplastic crisis w/ parvovirus B19

autosplenectomy (increased encapsulated bacteria infection risk)

splenic sequestration crisis

salmonella osteomyelitis

painful crisis (vaso-occlusive) - RBC stick, WBC and platelets interact and are activated, NO gets depleted

renal papillary necrosis