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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

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
How can you determine a megaloblastic anaemia?
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.
26
What is the name for the enlargement of red blood cells?
Macrocytosis
27
What is the name for RBCs being different sizes?
Anisocytosis
28
What is the name for RBCs being different shapes?
Poikilocytosis
29
Where is iron deposited in megaloblastic anaemias?
Skin, liver etc
30
What effects are there in other cells and tissues from megaloblastic anaemia?
Neutrophils and megakaryocytic large with hyper segmented nuclei, enlarged nuclei in gut epithelial cells
31
What is vitamin B12 required for?
The conversion (demethylation) of the transport form of folic acid, methyl-tetrafolate (me-FH4), to tetrahydrofolate (FH4).
32
What is the function of FH4?
It enables transport of one-carbon units and is required for thymidine synthesis
33
Where does vitamin B12 come from?
For humans it is dietary, and it comes from animal sources.
34
What is the minimum daily requirement of vitamin B12?
1μg
35
What is the average daily intake of vitamin B12?
100s μg
36
Where is vitamin B12 absorbed? What does it require in order to be absorbed?
In the terminal ileum, requires intrinsic factor from gastric mucosa.
37
Where is vitamin B12 stored and for how long?
In the liver for up to 5 years.
38
What is vitamin B12 deficiency caused by?
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
What is pernicious anaemia?
An intrinsic factor deficiency (not produced in stomach by parietal cells) due to autoimmune destruction of gastric mucosa.
40
Where does folate come from?
Humans are entirely dependant on dietary folate, e.g. from vegetables, fruit
41
What is the minimum daily requirement of folate?
50μg
42
What is the amount of folate in the average Western diet?
650μg, but 90% destroyed by cooking
43
Where is folate absorbed?
Jejunum
44
How long is folate stored for?
100 days
45
What is folate deficiency caused by?
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
What is the IF receptor (also for vitamin B12) called?
Cubilin
47
What does vitamin B12 bind in the stomach?
Haptocorrin
48
What does folate come as in the diet?
Folate polyglutamates
49
What is dyserythropoiesis?
Iron deficiency anaemia (erthyroblasts)
50
Which is the most common anaemia in the UK?
Iron deficiency anaemia
51
What is the commonest nutritional disease in the world?
Iron deficiency
52
What is the appearance of RBCs in dyserythropoiesis?
Microcytic, hypochromic, poikilocytosis
53
What is the daily requirement of iron in males and females?
7mg/day males | 15mg/day females
54
What is the average daily iron intake?
15-20mg
55
What is the major source of iron? How much of it is absorbed?
Haem/organic from animal produce (25% absorbed)
56
What is another source of iron? How much of it is absorbed?
Inorganic/non-haem iron from vegetable produce (5% absorbed)
57
What is the iron storage pool bound in normally? What is the iron bound in if there is iron overload?
Ferritin normally | Haemosiderin if iron overload
58
How is iron balance maintained?
Through regulation of iron absorption in the duodenum.
59
How is negative feedback about high levels of iron achieved?
Via hepcidin, which is released by the liver if iron levels rise too high and prevents iron absorption.
60
What happens to iron instead of being absorbed if levels are too high?
It is converted to ferritin in mucosal cells which are shed.
61
What are causes of iron deficiency?
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
What happens in severe iron deficiency?
Loss of function of iron-containing enzymes (e.g. cytochromes, catalase), leading to malabsorption and changes in nails, hair, tongue.
63
What are haemolytic anaemias? What are the two types?
Anaemias due to red cell destruction. 1) Extravascular, removal by macrophages, largely in spleen (which enlarges) 2) Intravascular, lysis within the circulation
64
What is the response to haemolytic anaemias?
Increased erythropoiesis, with expansion of red marrow and extra-medullary haemopoiesis.
65
What is different about the blood in haemolytic anaemias?
Increased numbers of reticulocytes, blood may contain erythroblasts.
66
What are the two broad causes of haemolytic anaemias? Which is normally hereditary and which is normally acquired?
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
What abnormalities intrinsic to the red cell are there?
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
What abnormalities extrinsic to the red cell are there?
Immune e.g. haemolytic disease of the newborn Physical e.g. valve replacements Chemical e.g. lead poisoning Infection e.g. malaria
69
What is a haemoglobinopathy and how do most occur?
Where there is production of structurally abnormal haemoglobin chains, occur due to mutation (90%) or deletion.
70
What is the most common haemoglobinopathy?
Sickle cell disease
71
What causes sickle cell disease? What is the abbreviation for sickle cell haemoglobin? What is the amino acid change in sickle cell disease?
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
What causes HbS to aggregate and polymerise in homozygotes with sickle cell disease?
Dehydration, infection, reduced o2 levels and low pH
73
What are the consequences of sickle cell disease?
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
How much of the body's haemoglobin is HbS in heterozygotes? What needs to happen for sickling to occur?
40%. Severe reduction in oxygen or drop in pH
75
What is the prevalence of heterozygosity of sickle cell disease in some African populations?
30%
76
What are the advantages for A/S children?
They are less likely to die of malaria and have reduced parasite density compared to A/A children.
77
What is the protection is A/S children probably due to?
Increased clearance of parasitised cells following sickling.
78
What are thalassaemias?
Diminished production of glob in chains of HbA.
79
What are the two consequences of thalassaemias?
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
Where are β chains encoded?
By a single gene on chromosome 11.
81
What do mutations of the β chain gene cause?
Either a loss of β chains (β0) or inadequate synthesis (β+)
82
What can mutations of the β chain gene affect?
Gene transcription RNA splicing Translation
83
What are other implications of β thalassamaemia?
Compensatory increase in HbF and sometime HbA2.
84
Which genotypes lead to β thalassaemia major and what does this cause?
β0/β0, β+/β+, β0/β+ | Severe anaemia
85
Which genotypes lead to β thalassaemia minor and what does this cause?
β0/β or β+/β | Mild anaemia
86
What does ineffective erythropoiesis lead to?
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
Where are α chains encoded? How much of the α globin protein does each gene contribute?
By two duplicated genes on each chromosome 16. Each gene contributes 25%.
88
What usually causes α thalassaemia?
Deletion of these genes. The levels of α chain synthesis are dependant on the number of deleted genes
89
Which are more soluble out of free β and γ chains and free α chains? Why is this significant?
Free β and γ chains. It means that ineffective haemopoiesis and haemolysis is less severe in α thalassaemia than β thalassaemia.
90
What genotype will 1 deletion lead to? What are the features of this disease?
-α/αα | It is a silent deletion
91
Which genotypes will 2 deletions lead to? What are the features of this disease?
--/αα or -α/α- | α thalassaemia trait (mild anaemia)
92
What genotype3 deletions lead to? What are the features of this disease?
-α/-- | HbH (β4) disease (severe anaemia)
93
What genotype will 4 deletions lead to? What are the features of this disease?
``` --/-- Hb Barts (γ4)disease (lethal in utero) ```

Biology of Disease (43 decks)

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