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Biology of Disease > Lecture 34 - Disorders of Red Blood Cells - Anaemia > Flashcards

Lecture 34 - Disorders of Red Blood Cells - Anaemia Flashcards

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1
Q

What is the definition of anaemia?

A

A reduction in the total circulating red cell mass, with reduced oxygen carrying capacity of the blood.

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2
Q

How is anaemia measured?

A

As a reduction in haemoglobin concentration of the blood.

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3
Q

What are the two ways in which anaemia can arise?

A

Because of an imbalance between the rate of production of red blood cells and the rate of loss or destruction.

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4
Q

What does HSC stand for?

A

Haematopoietic stem cells

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5
Q

What does GMP stand for?

A

Granulocyte macrophage progenitor

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6
Q

What does MEP stand for?

A

Megakaryocyte/erythroid progenitor

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7
Q

What are the two names for erythroid progenitors?

A

Erythroblasts (normoblasts) and reticulocytes.

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8
Q

Which cell types arise from the common lymphoid progenitor?

A

B cells, plasma cells, T helper cells, cytotoxic T cells and NK cells

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9
Q

Which cell types arise from the common myeloid progenitor?

A

Erythrocytes, platelets, neutrophils, monocytes, macrophages, eosinophils, basophils.

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10
Q

What is the RBC count in males compared to females?

A
  1. 5x10^12/l in males

5. 8x10^12/l in females

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11
Q

What is the haemoglobin count in males compared to females?

A
  1. 5g/dl in males

15. 0g/dl in females

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12
Q

What is the average diameter of an erythrocyte and what is the range of diameters?

A 
Average = 7.0 μm
Range = 6-9.5 μm
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13
Q

What is the RBC life span?

A

120 days

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14
Q

Where are RBCs destroyed? What causes them to be destroyed here?

A

Spleen, if they are unable to show enough flexibility to get through the spleen endothelium.

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15
Q

What is HbF and which chains does it have? What proportion of it is there in adults?

A

Normal fetal and neonatal haemoglobin, α2 γ2.

1% in normal adults.

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16
Q

What is HbA and which chains does it have? What proportion of it is there in adults?

A

The major form of normal adult haemoglobin, α2 β2.

96% in normal adults.

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17
Q

What is HbA2 and which chains does it have? What proportion of it is there in adults?

A

The minor form of normal adult haemoglobin, α2 δ2.

3% in normal adults.

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18
Q

How many normal haemoglobin variants are there that cause little or no disease?

A

Over 300.

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19
Q

What are the signs and symptoms of anaemia? (4)

A

1) Thin skin and nails
2) Pale mucous membranes
3) Hypoxic damage in viscera - myocardium, kidney, liver, brain.
4) Compensatory changes

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20
Q

What are the effects of hypoxic damage in viscera?

A

Weakness, malaise, easy fatiguability
Angina pectoris
Headache, dimness of vision, faintness

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21
Q

What are the compensatory changes seen in anaemia?

A

Raised cardiac output and rate
Increased breathing rate (often breathlessness on mild exertion)
Hyperplasia of haemopoietic tissue in bone marrow

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22
Q

What 3 main categories will all anaemias fall under?

A 
Impaired generations of RBCs or their constituents
Increased Destruction of RBCs
Blood Loss (Haemorrhage)
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23
Q

What is a dyserythropoiesis and what is it normally caused by?

A

Impaired DNA synthesis (megaloblastic anaemia).

Usually caused by a vitamin B12 or folic acid deficiency

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24
Q

What are vitamin B12 and folic acid coenzymes in?

A

Synthesis of thymidine (a nucleoside required in DNA)

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25
Q

How can you determine a megaloblastic anaemia?

A

Cells show impaired DNA synthesis. Nuclear maturation is defective and the cell does not divide. The cell continues to make RNA and protein and so enlarges.

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26
Q

What is the name for the enlargement of red blood cells?

A

Macrocytosis

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27
Q

What is the name for RBCs being different sizes?

A

Anisocytosis

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28
Q

What is the name for RBCs being different shapes?

A

Poikilocytosis

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29
Q

Where is iron deposited in megaloblastic anaemias?

A

Skin, liver etc

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30
Q

What effects are there in other cells and tissues from megaloblastic anaemia?

A

Neutrophils and megakaryocytic large with hyper segmented nuclei, enlarged nuclei in gut epithelial cells

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31
Q

What is vitamin B12 required for?

A

The conversion (demethylation) of the transport form of folic acid, methyl-tetrafolate (me-FH4), to tetrahydrofolate (FH4).

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32
Q

What is the function of FH4?

A

It enables transport of one-carbon units and is required for thymidine synthesis

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33
Q

Where does vitamin B12 come from?

A

For humans it is dietary, and it comes from animal sources.

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34
Q

What is the minimum daily requirement of vitamin B12?

A

1μg

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35
Q

What is the average daily intake of vitamin B12?

A

100s μg

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36
Q

Where is vitamin B12 absorbed? What does it require in order to be absorbed?

A

In the terminal ileum, requires intrinsic factor from gastric mucosa.

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37
Q

Where is vitamin B12 stored and for how long?

A

In the liver for up to 5 years.

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38
Q

What is vitamin B12 deficiency caused by?

A

Inadequate uptake (e.g. vegans)
Increased requirements (e.g. pregnancy, anaemia, malignancy)
Malabsorption due to gastric causes
Malabsorption due to pancreatic deficiency
Malabsorption due to ileal disease

39
Q

What is pernicious anaemia?

A

An intrinsic factor deficiency (not produced in stomach by parietal cells) due to autoimmune destruction of gastric mucosa.

40
Q

Where does folate come from?

A

Humans are entirely dependant on dietary folate, e.g. from vegetables, fruit

41
Q

What is the minimum daily requirement of folate?

A

50μg

42
Q

What is the amount of folate in the average Western diet?

A

650μg, but 90% destroyed by cooking

43
Q

Where is folate absorbed?

A

Jejunum

44
Q

How long is folate stored for?

A

100 days

45
Q

What is folate deficiency caused by?

A

Inadequate intake e.g. the elderly, chronic alcoholics
Increased requirements e.g. pregnancy, anaemia, malignancy
Inadequate absorption in small bowel disease e.g. coeliac
Impaired utilisation e.g. folic acid antagonist methotrexate

46
Q

What is the IF receptor (also for vitamin B12) called?

A

Cubilin

47
Q

What does vitamin B12 bind in the stomach?

A

Haptocorrin

48
Q

What does folate come as in the diet?

A

Folate polyglutamates

49
Q

What is dyserythropoiesis?

A

Iron deficiency anaemia (erthyroblasts)

50
Q

Which is the most common anaemia in the UK?

A

Iron deficiency anaemia

51
Q

What is the commonest nutritional disease in the world?

A

Iron deficiency

52
Q

What is the appearance of RBCs in dyserythropoiesis?

A

Microcytic, hypochromic, poikilocytosis

53
Q

What is the daily requirement of iron in males and females?

A

7mg/day males

15mg/day females

54
Q

What is the average daily iron intake?

A

15-20mg

55
Q

What is the major source of iron? How much of it is absorbed?

A

Haem/organic from animal produce (25% absorbed)

56
Q

What is another source of iron? How much of it is absorbed?

A

Inorganic/non-haem iron from vegetable produce (5% absorbed)

57
Q

What is the iron storage pool bound in normally? What is the iron bound in if there is iron overload?

A

Ferritin normally

Haemosiderin if iron overload

58
Q

How is iron balance maintained?

A

Through regulation of iron absorption in the duodenum.

59
Q

How is negative feedback about high levels of iron achieved?

A

Via hepcidin, which is released by the liver if iron levels rise too high and prevents iron absorption.

60
Q

What happens to iron instead of being absorbed if levels are too high?

A

It is converted to ferritin in mucosal cells which are shed.

61
Q

What are causes of iron deficiency?

A

Impaired absorption e.g. small bowel disease
Increased demand e.g. pregnancy, childhood
Chronic blood loss to exterior
- gastro-intestinal e.g. peptic ulcer, malignancy
- genito-urinary e.g. malignancy
Low dietary intake e.g. poverty, old age

62
Q

What happens in severe iron deficiency?

A

Loss of function of iron-containing enzymes (e.g. cytochromes, catalase), leading to malabsorption and changes in nails, hair, tongue.

63
Q

What are haemolytic anaemias? What are the two types?

A

Anaemias due to red cell destruction.

1) Extravascular, removal by macrophages, largely in spleen (which enlarges)
2) Intravascular, lysis within the circulation

64
Q

What is the response to haemolytic anaemias?

A

Increased erythropoiesis, with expansion of red marrow and extra-medullary haemopoiesis.

65
Q

What is different about the blood in haemolytic anaemias?

A

Increased numbers of reticulocytes, blood may contain erythroblasts.

66
Q

What are the two broad causes of haemolytic anaemias? Which is normally hereditary and which is normally acquired?

A

Abnormalities intrinsic to red cell - hereditary. Erythrocytes are deformed and cannot travel through the sinusoids in the spleen. Once trapped they are phagocytosed by macrophages.

Abnormalities extrinsic to red cell - acquired.

67
Q

What abnormalities intrinsic to the red cell are there?

A

Structural defects e.g. hereditary spherocytosis - defects in red cell skeleton produces deformed spheroidal cells
Enzyme defects e.g. pyruvate kinase deficiency - reduced ATP from glycolysis
Abnormalities of haemoglobin (haemoglobinopathies)

68
Q

What abnormalities extrinsic to the red cell are there?

A

Immune e.g. haemolytic disease of the newborn
Physical e.g. valve replacements
Chemical e.g. lead poisoning
Infection e.g. malaria

69
Q

What is a haemoglobinopathy and how do most occur?

A

Where there is production of structurally abnormal haemoglobin chains, occur due to mutation (90%) or deletion.

70
Q

What is the most common haemoglobinopathy?

A

Sickle cell disease

71
Q

What causes sickle cell disease? What is the abbreviation for sickle cell haemoglobin? What is the amino acid change in sickle cell disease?

A

A point mutation that changes a polar amino acid on the external surface of the β glob in protein. HbS (α2β2 6 glu → val).

72
Q

What causes HbS to aggregate and polymerise in homozygotes with sickle cell disease?

A

Dehydration, infection, reduced o2 levels and low pH

73
Q

What are the consequences of sickle cell disease?

A

Haemolysis, mostly in the spleen
Occlusion of the small blood vessels with reduced O2 delivery to organs (and more sickling) - especially in spleen, bone marrow, sites of inflammation where flow is slow
Tissue hypoxia/infarction can cause pain (bones, lungs, brain)
May also be chronic tissue hypoxia (affecting growth, kidneys, heart, lungs, etc.)

74
Q

How much of the body’s haemoglobin is HbS in heterozygotes? What needs to happen for sickling to occur?

A

40%. Severe reduction in oxygen or drop in pH

75
Q

What is the prevalence of heterozygosity of sickle cell disease in some African populations?

A

30%

76
Q

What are the advantages for A/S children?

A

They are less likely to die of malaria and have reduced parasite density compared to A/A children.

77
Q

What is the protection is A/S children probably due to?

A

Increased clearance of parasitised cells following sickling.

78
Q

What are thalassaemias?

A

Diminished production of glob in chains of HbA.

79
Q

What are the two consequences of thalassaemias?

A

Reduced production of RBCs (low glob in levels, red cells hypo chromic, microcytic. May be anisocytosis)
Relative excess of other chains (e.g. α4, β4) which precipitate as inclusions.

80
Q

Where are β chains encoded?

A

By a single gene on chromosome 11.

81
Q

What do mutations of the β chain gene cause?

A

Either a loss of β chains (β0) or inadequate synthesis (β+)

82
Q

What can mutations of the β chain gene affect?

A

Gene transcription
RNA splicing
Translation

83
Q

What are other implications of β thalassamaemia?

A

Compensatory increase in HbF and sometime HbA2.

84
Q

Which genotypes lead to β thalassaemia major and what does this cause?

A

β0/β0, β+/β+, β0/β+

Severe anaemia

85
Q

Which genotypes lead to β thalassaemia minor and what does this cause?

A

β0/β or β+/β

Mild anaemia

86
Q

What does ineffective erythropoiesis lead to?

A

Bone marrow expansion with erosion of cortical bone (e.g. skull)
Extra-medullary haemopoiesis (e.g. liver, spleen)
Excessive absorption of dietary iron, producing iron overload (e.g. heart).
Specules of bone projecting

87
Q

Where are α chains encoded? How much of the α globin protein does each gene contribute?

A

By two duplicated genes on each chromosome 16. Each gene contributes 25%.

88
Q

What usually causes α thalassaemia?

A

Deletion of these genes. The levels of α chain synthesis are dependant on the number of deleted genes

89
Q

Which are more soluble out of free β and γ chains and free α chains? Why is this significant?

A

Free β and γ chains. It means that ineffective haemopoiesis and haemolysis is less severe in α thalassaemia than β thalassaemia.

90
Q

What genotype will 1 deletion lead to? What are the features of this disease?

A

-α/αα

It is a silent deletion

91
Q

Which genotypes will 2 deletions lead to? What are the features of this disease?

A

–/αα or -α/α-

α thalassaemia trait (mild anaemia)

92
Q

What genotype3 deletions lead to? What are the features of this disease?

A

-α/–

HbH (β4) disease (severe anaemia)

93
Q

What genotype will 4 deletions lead to? What are the features of this disease?

A 
--/--
Hb Barts (γ4)disease (lethal in utero)

Biology of Disease (43 decks)

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