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CSI > CSI 2 > Flashcards

CSI 2 Flashcards

1
Q

What are harm groups made of

A

Porphyrin ring bound to a ferrous iron ion (Fe2+)

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2
Q

What does oxygen bind to in the harm groups?

A

The Fe2+ ion

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3
Q

How many functional globin chains are there

A

8

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4
Q

What are the functional globin chains?

A

Alpha 1, Alpha 2, Beta, A Gamma, G Gamma, Delta, Epsilon, Zeta

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5
Q

What is the alpha globin cluster made of?

A

5’ zeta, alpha 2, alpha 1 3’

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6
Q

What is the beta globin cluster made of?

A

5’ epsilon, G gamma, A gamma, delta, beta 3’

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7
Q

Which globin chains make up HbA?

A

2 alpha and 2 beta

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8
Q

Which globin chains make up HbA2?

A

2 alpha and 2 delta

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9
Q

Which globin chains make up fetal haemoglobin?

A

2 alpha and 2 gamma

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10
Q

What does P50 mean

A

The value at which 50% of the harm groups have oxygen bound

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11
Q

What is the P50 of myoglobin?

A

2 torr

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12
Q

What is the P50 of haemoglobin?

A

26 torr

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13
Q

What is fractional saturation?

A

The fraction of haem groups that have oxygen bound

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14
Q

What curve is for haemoglobin?

A

Sigmoidal oxygen dissociation curve

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15
Q

Where is myoglobin found?

A

Muscles

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16
Q

What is ppO2 in the lungs like?

A

100 torr -> haemoglobin becomes highly saturated with oxygen

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17
Q

What is the ppO2 in the tissues like?

A

20 torr -> Haemoglobin releases around 66% of its oxygen

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18
Q

What is positive cooperativity?

A

Once an oxygen molecule binds to one haem group, it becomes easier for oxygen to bind to the next haem group within the molecule

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19
Q

What is 2,3-BPG?

A

It’s an allosteric effector that binds to a site in deoxyhaemoglobin and stabilises the structure

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20
Q

What is the effect of 2,3-BPG?

A

It decreases the affinity of haemoglobin for oxygen. This shifts the curve to the right. This is what allows the haemoglobin to act as an effective oxygen carrier.

Haemoglobin in the absence of 2,3-BGP does not have the sigmoidal shaped oxygen dissociation curve

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21
Q

How is 2,3-BGP generated?

A

Through the Rapoport-Leubering Shuttle

In the shuttle, some of the 1,3-BGP produced in glycolysis is converted into 2,3-BPG by movement of a phosphate group.

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22
Q

Which enzyme catalyses formation of 2,3-BPG?

A

Bisphosphoglycerate mutase (BPGM)

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23
Q

What happens in rapidly respiring cells?

A

Pyruvate is decarboxylated to acetyl coA forming CO2

Pyruvate is converted to lactate so pH decreases

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24
Q

How does pH and CO2 affect haemoglobin?

A

H+ ions and CO2 are allosteric effectors which bind to sites in haemoglobin and decrease the affinity for oxygen so oxygen is released when RBCs enter the tissues

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25
Q

How does age affect globin gene expression?

A

A foetus would produce more alpha and gamma goblins.

After birth, there is more production of beta goblins and less production of gamma globins.

A very small amount of HbF persists throughout adult life.

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26
Q

Other than sickling, what can be seen in the blood of people with SCA

A

More HbF than people without SCA to compensate

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27
Q

How does the gamma chain differ from a beta chain?

A

One single amino acid substitution

28
Q

What does the difference in structure of the gamma and beta chain lead to?

A

Gamma chains have decreased affinity for 2,3-BPG and thus and increased affinity for oxygen

29
Q

Why does HbF need a higher affinity for O2?

A

It obtains oxygen from maternal HbA, not the air

30
Q

What is expected in a sickle cell vs normal haemoglobin electrophoresis?

A

HbA would run further towards the positive electrode as it is more negatively charged

31
Q

Why is there a difference in charge between HbS and HbA

A

Point mutation in Beta chain.

Glutamate in normal (hydrophilic, negatively charged) is replaced by valine (hydrophobic, uncharged)

32
Q

What causes sickle cell?

A

HbA contains 2 alpha and beta chains like HbA.

But there is a mutation at codon 6 of the beta globin gene. A glutamate is replaced by a valine molecule at position 6.

Glutamate : negative, polar, hydrophilic, soluble

Valine: neutral, nonpolar, hydrophobic, insoluble

33
Q

In terms of affinity, how does HbS differ from HbA

A

Lower affinity than HbA

34
Q

How does baseline haemoglobin concentration with SCA differ from normal?

A

About half the concentration compared to normal

35
Q

How do patients with HbS not experience symptoms such as tiredness, breathlessness and heart palpitations

A

If people with HbA had the same baseline haemoglobin as HbS, they would experience those symptoms. But HbS has lower affinity in comparison so oxygen is readily supplied so the symptoms are not caused.

36
Q

What are the main symptoms of sickle cell

A

1) painful crises that can last up to a week
2) anaemia which can cause tiredness and shortness of breath
3) An increased risk of serious infections

37
Q

What is sickle cell genetically?

A

A recessive condition

38
Q

How would someone know if they have sickle cell disease?

A

Screening is offered to all pregnant women in England to check the risk of the baby being born with the condition.

All babies are offered screening as part of the newborn blood spot test (heel prick test)

Blood tests can also be carried out at any age to check for the disease or if you are a carrier.

39
Q

What are the treatments for sickle cell disease?

A

1) Drinking plenty of fluids and staying warm to prevent painful episodes
2) Painkillers, such as paracetamol or ibuprofen
3) Daily antibiotics and having regular vaccinations to reduce your chances of getting an infection
4) medicine e.g hydroxycarbamide
5) Regular blood transfusions if symptoms continue or get worse; or there are any signs of damage
6) Emergency blood transfusion if severe anaemia develops

40
Q

What are the cures for sickle cell?

A

Stem cell or bone marrow transplant

Not done often due to risks involved

41
Q

How is SCA inherited

A

It follows an autosomal recessive inheritance pattern

42
Q

What happens during deoxygenating in haemoglobin?

A

Haemoglobin S undergoes a conformational change here. The hydrophobic valine residues protrude from the surface and causes hydrophobic interactions between the HbS molecules resulting in the formation of fibres.

43
Q

What do the fibres formed by valine during deoxygenation do?

A

They distort the shape of the RBC which results in the sickly form of the cell

44
Q

What methods can be used to detect sickle cell

A

1) Electrophoresis
2) Solubility (in presence of sodium dithionite - a reducing agent - the solubility of sickle cells decreases as oxy HB is converted to deoxy Hb: but this does not differentiate AS from SS)
3) Blood film

45
Q

How long do sickle cells last and why

A

20 days (compared to 120) because repeated sickling weakens the membrane and causes haemolysis which results in anaemia

46
Q

What may you see in patients whose sickle cells are undergoing haemolysis

A

Jaundice and gallstones as bilirubin is released to break down the blood cells and it’s a yellow substance

47
Q

What is Vaso-occlusion?

A

It is the blockage of the micro-circulation due to rigid sickle cells getting stuck resulting in the blockage of blood flow to parts of the body.

Adhesion also occurs due to binding of sickle cells to p-selectin on blood vessels.

Sickle cells also tend to aggregate together

This leads to ischaemia and necrosis

48
Q

What is bone crises

A

Blockage of blood flow to the bone marrow

49
Q

Why can sickle cell lead to stroke

A

Blockage of blood flow to the brain tissue leading to ischaemic stroke. Collateral vessels form to circumvent the blockage but they are very fragile and so are more likely to rupture if there is blockage which would lead to haemorrhaging stroke.

50
Q

Why can sickle cell lead to vision loss

A

Blood blockage in the micro vessels in the retina. This damages the vessels and lead to the formation of collateral vessels which are weaker and could rupture leading to haemorrhage.

51
Q

Triggers of Vaso-occlusive crises

A

Exercise leading to Hb deoxygenation
Cold temperatures leading to vasoconstriction
Dehydration leading to increased blood viscosity

52
Q

What genetic makeup causes sickle cell anaemia

A

HbSS

53
Q

What genetic makeup causes sickle cell trait?

A

HbAS

54
Q

What are reticulocutes

A

Immature RBCs

55
Q

What happens to reticulocyte levels in sickle cell disease?

A

Increased as a compensatory mechanism

56
Q

What is splenomegaly?

A

Accumulation of degraded erythrocytes increases the size of the spleen

57
Q

What is dactylitis?

A

Pain in hand joints due to blood vessels being occluded and less oxygen delicery

58
Q

What is splenic sequestration?

A

Large volume of blood pooled in spleen - sudden drop in Hb

59
Q

What may multiple blood transfusions lead to?

A

Hemosciderosis which can damage liver, heart, pancreas and other organs leading to diabetes mellitus

60
Q

What is wrong with using hydroxycarbamide

A

Increased risk of infection

61
Q

How to treat crises

A

Painkillers (aspirin and ibuprofen)
Severe pain treated using opioid (morphine) daily meds

62
Q

How can crises symptoms be alleviated?

A

Keeping warm
Constant hydration
Avoiding locations exposed to high altitudes and low oxygen levels

63
Q

How does hydroxycarbamide work?

A

It stimulates synthesis of HbF
Hydroxyurea further suppresses marrow production of reticulocytes and neutrophils which reduces Vaso-occlusion since neutrophils promote vascular adhesion)

64
Q

What increases sickling?

A

Acidosis
Low flow blood vessels

65
Q

What three amino acids make the hydrophobic pocket

A

Alanine, phenylalanine, leucine

CSI (3 decks)

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