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Medicine Sem 2 > Case 7 > Flashcards

Case 7 Flashcards

1
Q

what’s the name of a committed stem cell that produces erythrocytes?

A

colony-forming unit-erythrocyte (CFU-E)

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2
Q

what’s the name of the colony forming unit that produce myeloid cells?

A

CFU-GEMM - they give rise to granulocytes, erythrocytes, monocytes and megakaryocytes (giving rise to platelets)

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3
Q

How are PHSCs identified?

A

using immunological testing - they present with CD34+ and CD38- on their surface

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4
Q

what is growth and reproduction of the different stem cells controlled?

A

by multiple proteins called growth inducers

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5
Q

what are the different growth inducers?

A
  • stem Cell Factor (SCF)
  • granulocyte macrophage colony stimulating factor (GM-CSF)
  • granulocyte colony stimulating factor (G-CSF)
  • macrophage colony stimulating factor (M-SCF)
  • IL-3
  • IL-5
  • erythropoietin
  • thrombopoietin
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6
Q

what are the specific differentiation inducers for different types of committed cells?

A
  • PU.1: causes differentiation of cells along the myeloid lineage
  • GATA-1: this causes differentiation of cells along the erythropoietic and megakaryocytic cell lineages
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7
Q

what does stem cell factor do?

A

it synergises with cytokines such as IL-3 and GM-CSF to increase proliferation of stem cells

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8
Q

what does GM-CSF do?

A
  • necessary for the growth and development of granulocyte and macrophage progenitor cells
  • stimulates myeloblasts and monoblasts
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9
Q

what does G-CSF do?

A

similar to M-but acts on precursor cells which give rise to neutrophils

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10
Q

what does M-CSF do?

A

plays a role in proliferation and differentiation of haematopoietic stem cells to produce monocytes and macrophages

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11
Q

what does IL-3 do?

A

works in conjunction with GM-CSF to proliferate most haematopoietic progenitor cells

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12
Q

what does IL-5 do?

A
  • produced by T lymphocytes

- plays a role in growth and differentiation of eosinophils

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13
Q

what does thrombopoietin do? and where’s it produced?

A
  • mainly produced in the liver

- stimulates megakaryocytes and platelet production (thrombopoiesis)

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14
Q

formation of the growth inducers and differentiation inducers is itself controlled by factors outside the bone marrow - give examples.

A

erythrocytes: exposure of blood to low oxygen for a long time causes growth induction, differentiation and production of greatly increased numbers of erythrocytes
infectious diseases cause growth, differentiation and formation of specific types of leucocytes that are needed to combat the infection

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15
Q

what’s the average volume of the red blood cell?

A

90-95cm3

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16
Q

what is the normal range of the mean corpuscular volume?

A

80-99 femtolitres (fL)

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17
Q

what allows the red blood cell to change shape and not rupture?

A

the normal cell has a great excess of cell membrane for the quantity of material inside, deformation does not stretch the membrane great and, consequently, does not rupture the cell

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18
Q

where are erythrocytes produced during embryonic life through to adult life?

A

Embryonic life
- early weeks of embryonic life = primitive, nucleated RBCs produced in the yolk sac
- middle trimester of gestation: liver (mainly), spleen and lymph nodes
- last month of gestation and after birth = bone marrow
The bone marrow of all bones produce erythrocytes until the age of 5 years
The marrow of long bones, except for the proximal portions of the humeri and tibiae, is gradually replaced by adipose tissue (yellow marrow) and produces no more red blood cells after the age of 20 years
Beyond this age, the erythrocyte production is confined to the axial skeleton and the proximal ends of the long bones - this includes marrow of the membranous bones, such as the vertebrae, sternum, ribs and ilia - even in these bones, the marrow becomes less productive as age increases

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19
Q

describe the genesis of erythrocytes

A
  1. the first cell that can be identified as belonging to the red blood cell series is the proerythroblast
    - this is formed from the CFU-E stem cells
  2. proerythroblast divides multiple times, forming the other stem cells and eventually forming a basophil erythroblast
    - these have very little haemoglobin
  3. basophil erythoblast divides multiple times, forming polychromatophil erythoblast and then orthochromatic erythroblast
    - haemoglobin increases between these generations until hitting 34%
    - the nucleus/endoplasmic reticulum condense to a smaller size between these generations until nothing is left
  4. at the reticulocyte stage, the cell still contains remnants of cytoplasmic organelles
    - during this stage the cell passes from the bone marrow into the bone capillaries by diapedesis
    - it takes around 5 days to reach this stage from the CFU-E stem cell
    - the normal reticulocyte count is around 1% - clinically this reticulocyte percentage is a useful indicator of erythropoiesis
  5. the remaining basophilic material in the reticulocyte normally disappears within 1 to 2 days, and the cell is then a mature erythrocyte
  • Blood stem cell -> myeloid stem cell
  • Proerythroblast: large cell with cytoplasm that stains dark blue
  • Give rise to erythroblasts (early & late)
  • Normoblasts: smaller cells cytoplasm start to stain lighter blue – late normoblasts have extruded nucleus
  • Reticulocyte: contains some ribosomal RNA circulates in peripheral blood (1-2 days)
  • Endpoint: mature RBC (erythrocyte) – RNA lost
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20
Q

where is erythropoietin produced?

A

kidneys - 90%

liver - 10%

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21
Q

how does hypoxia lead to increased erythropoietin production?

A
  • renal tissue hypoxia leads to increased tissue levels of hypoxia-inducible factor-1 (HIF-1)
  • this serves as a transcription factor for a large number of hypoxia-inducible genes, including the erythropoietin gene
  • HIF-1 binds to a hypoxia response element residing in the erythropoietin gene, inducing transcription of mRNA and, ultimately, increased erythropoietin synthesis
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22
Q

what stimulates erythropoietin production?

A

noradrenaline, adrenaline and several prostaglandins

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23
Q

how long does erythropoietin take to produce new RBCs?

A

around 5 days

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24
Q

what is the life span of an erythrocyte?

A

120 days

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25
Q

what do the cytoplasmic enzymes in red blood cells do?

A
  • metabolise glucose and form small amounts of ATP
  • maintain pliability of the cell membrane
  • maintain membrane transport of ions
  • keep the iron of the cells’ haemoglobin in the ferrous form rather than ferric form
  • prevent oxidation of the proteins in the red cells
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26
Q

what happens to red blood cells as they get older? and what happens to its components?

A
  • the metabolic systems of old red cells become progressively less active and the cells become more and more fragile
  • once fragile enough, the cells rupture during passage through the red pup of the spleen
  • the content of the red blood cell, i.e. haemoglobin, is released and is phagocytosed by the macrophages in many parts of the body - especially by Kupffer cells in the liver and macrophages of the spleen (white pulp) and the bone marrow
  • this causes release of Fe2+ into the blood which is carried by transferrin to the bone marrow for production of new erythrocytes or to the liver for storage as ferritin
  • the porphyrin portion of the haemoglobin molecule is converted by the macrophages to bilirubin, which is released into the blood and later removed from the body by secretion through the liver into the bile
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27
Q

what can the concentration of haemoglobin in the blood go up to?

A

erythrocytes have the ability to concentrate haemoglobin in the cell fluid up to 34g in each 100 ml of cells - the concentration does not rise above this value because this is the metabolic limit of the cell’s haemoglobin-forming mechanism

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28
Q

what is the average amount of haemoglobin in men’s and women’s blood?

A

men’s blood contains an average of 15g of haemoglobin per 100ml of cells
women’s blood contains an average of 14g per 100 ml

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29
Q

how much oxygen is each gram of pure haemoglobin capable of combining with?

A

1.34 ml

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30
Q

when and where does the formation of haemoglobin start and when does it continue to?

A

begins in the mitochondria of the proerythroblasts and continues even into the reticulocytes stage of the red blood cells

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31
Q

what is haemoglobin formed from?

A
  • 2 Succinyl-CoA molecules bind with 2 glycine molecules to form a pyrrole molecule
  • 4 pyrroles combine to form protoporphyrin IX
  • protoporphyrin IX then combines with iron to form the heme molecule
  • each heme molecule combines with a globin chain (alpha, beta, gamma, delta) - forming a haemoglobin chain
  • 2 alpha-chains and 2 beta-chains combine to form haemoglobin A (HbA)
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32
Q

what are the variations in haemoglobin?

A
  • there are several slight variations in the different subunit haemoglobin chains, depending on the amino acid composition of the polypeptide chain
  • ## the different types of globin chains are designated alpha chains, beta chains, gamma chains, and delta chains
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33
Q

how does oxygen bind to the haemoglobin?

A

oxygen binds loosely with one of the coordination bonds of the iron atom - this is an extremely loose bond, so the combination is easily reversible

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34
Q

what determines the binding affinity of the haemoglobin for oxygen?

A

the types of haemoglobin chains in the haemoglobin molecule

  • HbA comprises about 97% of the Hb in adults
  • HbA2 (alpha2delta2) and HbF (alpha2gamma2), are found in adults in small amounts (1.5%)
  • HbF is the predominant type in the foetus
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35
Q

what are the two conformations that the haemoglobin molecule exists as?

A

R and T

  • the T (taut) conformation of deoxyhaemoglobin is characterised by the globin units being held tightly together by electrostatic bonds
  • these bonds are broken when oxygen binds to haemoglobin, resulting in the R (relaxed) conformation in which the remaining oxygen binding sites are more exposed and have a much higher affinity for oxygen than in the T conformation
  • the binding of one oxygen molecule to deoxyhaemoglobin increases the oxygen affinity of the remaining binding sites - this property is known as ‘cooperativity’ and is the reason for the sigmoid shape of the oxygen dissociation curve
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36
Q

what does 2,3-diphosphoglycerate do?

A

in the ‘open’ deoxygenated state, it (a product of red cell metabolism) binds to the haemoglobin molecule and lowers its oxygen affinity

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37
Q

what does liver secrete, where does it go and what does it do?

A

liver secretes apotransferrin into the bile, which flows through the bile ducts into the duodenum, where it enters the duodenal circulation
- the intestinal cells secrete free iron into the duodenal circulation
- the apotranferrin binds with the free iron forming transferrin
- the iron is loosely bound in the transferrin and, consequently, can be released to any tissue cell at any point in the body
Transferrin is then transported to the liver or the bone marrow:
- liver: here it enters the hepatocytes and combines with apoferritin, forming ferritin (storage molecule)
-bone marrow: here it binds to receptors on the erythroblasts, delivering iron to the mitochondria for the production of haemoglobin

38
Q

describe granulopoiesis

A
  • myeloblasts of varying size, large nucleus and no cytoplasmic granules are the first committed cells
  • they form promyelocytes which comprise of primary cytoplasmic granules
  • these form myelocytes depending on the cell type (smaller cells with specific cytoplasmic granules and no noticeable nucleoli)
  • these form metamyelocytes: these are non-dividing cells (mature into cells), with an indented nucleus and many cytoplasmic granules
39
Q

neutrophils:
- percentage of leucocytes
- describe them
- function
- raised count indicates what

A
  • constitute 40-75% of circulating leucocytes
  • mature neutrophils five lobes, less mature neutrophils have fewer lobes (polymorphs)
  • they are the first leucocyte to arrive at the site of infection
  • raised neutrophil count indicates an acute inflammatory response and is seen in association with bacterial infections
40
Q

eosinophils:

  • percentage of leucocytes
  • production stimulated by what
  • lifecycle
  • raised count indicates what
A
  • constitute 1-6% of leucocytes
  • bone marrow production is stimulated by IL-5 and to a lesser extent IL-3
  • eosinophils circulate in the blood for 8-12 hours and emigrate from capillaries to enter tissues
  • raised eosinophil count indicates helminthic parasitic infection and type 1 hypersensitivity reactions
41
Q

basophils:

  • percentage of leucocytes
  • production stimulated by what
  • function
  • raised count indicates what
A
  • constitutes less than 1% of leucocytes
  • IL-3 promotes basophil formation
  • IgE binds to the surface receptors of basophils and causes the cell to degranulate releasing inflammatory mediators
  • raised basophil count indicates myeloproliferative disorders (excess cells produced in the bone marrow)
42
Q

describe monopoiesis

A
  • monoblast is the first committed cell
  • this divides and differentiates into a promonocyte - a promonocyte is a large cell with indented nucleus only found in bone marrow
  • this differentiates into the mature monocyte
43
Q

Monocytes:

  • percentage of leucocytes
  • lifecycle
  • raised count indicates what
A
  • constitutes 2-10% of circulating leucocytes
  • circulate for 2-4 days before emigrating into tissues and differentiating into macrophages
  • raised monocyte count indicates chronic bacterial infections
44
Q

describe lymphopoiesis

A
  • B lymphocyte differentiation in foetus occurs in the liver but in adults occurs in the bone marrow
  • B lymphocytes mature into plasma cells
  • plasma cells are formed in the lymph nodes and themselves produce antibodies
  • T lymphocytes tend to mature in the thymus
  • natural killer cells are large cells with cytoplasmic granules
  • lymphoblast
  • prolymphocyte
45
Q

lymphocytes:

  • percentage of leucocytes
  • lifespan
  • raised count indicates what
A
  • constitues 20-50% of circulating leucocytes
  • lifespan: varies from weeks to years
  • raised lymphocyte count indicates viral infections
46
Q

what are some causes of macrocytic anaemia?

A
  • vitamin B12 deficiency
  • folate deficiency
  • alcohol excess (liver disease)
47
Q

what are some causes of normocytic anaemia?

A
  • acute blood loss
  • anaemia of chronic disease
  • pregnancy
  • bone marrow failure/suppression
48
Q

what are some causes of microcytic anaemia?

A
  • iron-deficiency anaemia

- thalassaemia

49
Q

what is MCV? what is the normal range?

A

a measure of the average red blood cell volume - normal range is 80-99fL

50
Q

What causes reduced production of RBCs?

A

deficiencies:
- iron-deficiency
- folate deficiency
- vitamin B12 deficiency
Non-deficiencies:
- anaemia of chronic disease
- cancers

51
Q

what are causes of increased destruction/loss of RBCs?

A
  • blood loss
  • sickle cell disease
  • thalassaemia
  • erythrocyte membrane defects: spherocytes, elliptocytes
  • cancers e.g. marrow cancer
  • haemolytic disease of the newborn
  • incompatible blood transfusion
  • infection
52
Q

what is the iron storage pool? how much iron does it contain? and where’s it found?

A
  • its represented by hemosiderin and ferritin-bound iron
  • contains on average 15% to 20% of total body iron (80% found in haemoglobin)
  • stored iron is found mainly in the liver, spleen, bone marrow and skeletal muscle
53
Q

what is serum ferritin a good indicator of? and why?

A

because it’s largely derived from the storage pool of iron, its concentration is a good indicator of the adequacy of body iron stores

54
Q

describe the absorption of iron?

A
  • iron is absorbed in the duodenum, where it must pass through the apical and basolateral membranes of enterocytes

non-heme iron is carried across each of these two membranes by distinct transporters:

  • after reduction by ferric reductase (from Fe3+ to Fe2+), the reduced iron is transported by the divalent metal transporter (DMT1) across the apical membrane into the cytoplasm
  • two proteins are then required for the basolateral transfer of iron to transferrin in the plasma - ferroportin which acts as a transporter and hephaestin which oxidises the iron

Both DMT1 and ferroportin are widely distributed in the body and are involved in iron transport in other tissues as well
Only a fraction of the iron that enters the cell is delivered to plasma transferrin by the action of ferroportin
- the remainder is bound to ferritin and lost through the exfoliation of mucosal cells

55
Q

what are the causes of iron deficiency anaemia?

A
  • insufficient dietary intake
  • malabsorption (e.g. coeliac disease)
  • increased physiological demands
  • chronic blood loss
56
Q

what can vitamin B12 deficiency anaemia be caused by?

A
  • can be caused by malabsorption of the vitamin
  • e.g. pernicious anaemia
  • deficiencies due to diet are rare
57
Q

what is pernicious anaemia?

A

this term is used to describe vitamin B12 deficiency resulting from the inadequate gastric (parietal cells) production or defective function of intrinsic factor

58
Q

what does pernicious anaemia stem from? describe what happens.

A

tends to stem from an autoimmune reaction against parietal cells and intrinsic factor itself, which produces gastric mucosal atrophy

  1. peptic digestion releases dietary vitamin B12, which then binds to salivary B12-binding proteins called R binders
  2. R-B12 complexes are transported to the duodenum and processed by pancreatic proteases; this releases B12, which attaches to intrinsic factor secreted from the parietal cells of the gastric fundic mucosa
  3. the intrinsic factor-B12 complex passes to the distal ileum and attaches to the epithelial intrinsic factor receptors, which leads to absorption of vitamin B12
  4. the absorbed B12 is bound to transport proteins called transcobalamins, which then deliver it to the liver (stored here) and other cells of the body

In pernicious anaemia, the intrinsic factor-B12 complex doesn’t form - this leads to decreased absorption of vitamin B12

59
Q

why does the administration of folates improve anaemia of vitamin B12 deficiency?

A

vitamin B12 is required for recycling of tetrahydrofolate and hence its deficiency reduces the availability of the form of folate that is required for DNA synthesis

60
Q

what are the causes of folate deficiency anaemia?

A
  1. diet/decreased intake: folate is widely prevalent in nearly all foods but is readily destroyed by 10 to 15 minutes of cooking
  2. increased requirements
  3. impaired utilisation
61
Q

why is folate important?

A
  • dihydrofolate is converted to tetrahydrofolate by the enzyme dihydrofolate reductase
  • tetrahydrofolate acts as an acceptor and donor of one-carbon units in a variety of steps involved in the synthesis of purines and thymidylate, the building blocks of DNA
  • its deficiency accounts for the inadequate DNA synthesis that is characteristic of megaloblastic anaemia
62
Q

what’s a difference between vitamin B12 deficiency anaemia and folate deficiency anaemia?

A

no neurologic abnormalities occur with folate deficiency

63
Q

what is sickle cell disease?

A

genetic variation in B globin chain of Hb molecule (HbS)

  • point mutation in the 6th codon of B-globin that leads to the replacement of a glutamate residue with a valine residue
  • an individual can be homozygous (HbS, HbS) or heterozygous (HbA, HbS)
  • heterozygous individuals are carriers of the sickle cell trait
64
Q

in a homozygous sickle cell individual, what is almost all of the haemoglobin in the red cell?

A

HbS (alpha2betaS2)

65
Q

what happens to the haemoglobin molecule in SSD? what does this cause?

A
  • it becomes unstable in low oxygen conditions leading to the formation of insoluble rigid chains
  • this causes vaso-occlusion and destruction of the red cell
  • sickled red cells are also mechanically fragile, leading to some intravascular haemolysis
66
Q

what is the pathogenesis of sickle cell disease?

A
  • HbS molecules undergo polymerisation when deoxygenated
  • initially the red cell cytosol converts from a freely flowing liquid to a viscous gel as HbS aggregates form
  • with continued deoxygenation aggregated HbS molecules assemble into long needle-like fibres within red cells, producing a distorted sickle shape
  • the presence of HbS underlies the major pathologic manifestations:
    1. chronic haemolysis
    2. microvascular occlusions - sickle red cells express higher than normal levels of adhesion molecules and are sticky
    3. tissue damage: this is as a result of the microvascular occlusions causing certain tissue to become hypoxic as a result of ischaemia
67
Q

what are the clinical features of sickle cell disease?

A
  • anaemia
  • stroke
  • acute chest syndrome
  • infections: increased susceptibility to infection with encapsulated organisms as a result of altered splenic function, which is severely impaired in children by congestion and poor blood flow and completely absent in adults because of splenic infarction
  • visual loss: vaso-occlusion in the retina
  • impaired growth and development: chronic hypoxia
  • chronic organ damage: kidneys, lungs, joints, heart: chronic hypoxia
68
Q

what is thalassaemia?

A
  • a group of inherited disorders resulting in reduced production of one or more globin chains

This results in an imbalance of globin chains and many pathological effects:

  • damage to red cell precursors, leading to ineffective erythropoiesis
  • damage to mature red cells, leading to haemolytic anaemia
69
Q

what are the two main types of thalassaemia?

A
  1. alpha thalassaemia (alpha chains)
    - caused by deficient synthesis of alpha-chains
    - controlled by 4 genes (2 from each parent)
    - there are four alpha-globin genes and the severity of alpha-thalassaemia depends no how many alpha-globin genes are affected
    - the anaemia stems both from a lack of adequate haemoglobin and the effects of excess unpaired non-alpha chains, which vary in type at different ages

silent carrier state:

  • associated with the deletion of a single alpha-globin gene, which causes a barely detectable reduction in alpha-globin chain synthesis
  • asymptomatic, but they have slight microcytosis

alpha-thalassaemia trait:

  • deletion of two alpha-globin genes from a single chromosome - Asian
  • deletion of one alpha-globin gene from each of the two chromosomes - African
  • both genotypes produce similar quantitative deficiencies of alpha-globin and are clinically identical, but have different implications for the children of affected individuals
  • as a result, symptomatic alpha-thalassaemia is more commonly found in Asian populations
  • if three genes are mutated, the individual will suffer from lifelong anaemia
  • if four genes are mutated, it is termed alpha-thalassaemia major and leads to death during pregnancy
  1. beta thalassaemia (B chains)
    - caused by deficient synthesis of B-chains
    - B0 mutations - associated with absent B-globin synthesis
    - B+ mutations - characterised by reduced B-globin synthesis
    - controlled by 2 genes (1 from each parent)
70
Q

what do these alpha/beta chain imbalances lead to?

A

haemolysis and anaemia

71
Q

what does the erythropoietic drive in the setting of severe anaemia lead to?

A
  • massive erythroid hyperplasia in the marrow and extensive extramedullary haematopoiesis
  • the expanding mass of red cell precursors erodes the bony cortex, impairs bone growth and produces skeletal abnormalities
72
Q

what does extramedullary haematopoiesis involve?

A

the liver, spleen and lymph nodes

73
Q

how does systemic iron overload occur?

A
  • excessive absorption of dietary iron due to ineffective erythropoiesis
  • ineffective erythropoiesis suppresses the circulating levels of hepcidin, a critical negative regulator of iron absorption
  • low levels of hepcidin and the iron load of repeated blood transfusion inevitably lead to severe iron overload
74
Q

what are clinical features of thalassaemia due to anaemia and due to iron overload?

A

anaemia:
- failure to grow and develop
- gross enlargement of liver and spleen
- skull deformities
- death in children/teens (if untreated)
iron overload:
- failure to grow and mature
- organ damage due to iron deposition
- cardiac
- liver
- endocrine
- death in early adulthood due to cardiac/liver disease

75
Q

what are agglutinogens and agglutinins?

A 
agglutinogen = antigen 
agglutinin = antibody
76
Q

when do antibodies form?

A
  • immediately after birth, the quantity of antibodies in the plasma is almost zero
  • after birth, an infant begins to produce antibodies against other types of antigens - e.g. if the infant is blood type A, it will produce anti-B antibodies - this is usually triggered because small amounts of type A and B antigens enter the body in food and in other ways
  • a maximum amount is usually reached by 10 years of age and this gradually declines throughout the remaining years of life
77
Q

which antigens does the Rhesus blood group system look at?

A

C, c, D, E and e

78
Q

what is haemolytic disease of the newborn?

A
  • this condition develops in a foetus, when the IgG antibodies produced by the mother pass through the placenta (should the foetus have a different blood group to the mother)
  • the red blood cells in the foetal circulation are destroyed and the foetus can develop reticulocytosis and anaemia
79
Q

what is the treatment to prevent haemolytic disease of the newborn? how does it work?

A
  • rhesus-negative mothers who have had a pregnancy who are pregnant with a rhesus-positive infant are offered Rh immune globulin (RhIG) at 28 weeks during pregnancy, at 34 weeks and within 48 hours after delivery to prevent sensitisation to the D antigen
  • it works by binding the anti-D antibodies in the injection to foetal red cells with the D antigen before the mother is able to produce an immune response and form anti-D IgG
  • D negative mother and D positive father -> heterozygous dominant
  • Rh negative mother carrying a Rh-positive baby
  • During pregnancy some of the foetal red blood cells can transfer from the baby to the mother across the placenta – there are certain risk periods where this is more likely
  • If the mother is exposed to the D red cells, then in the spleen the body reacts by manufacturing anti-D antibodies because it’s recognised as a foreign protein
  • Then those antibodies go back into the foetal circulation and destroy the foetal red blood cells
  • Can result in anaemia in the baby in utero which can be fatal if severe
  • Baby can get brain damage due to high levels of bilirubin
80
Q

what is a supererogatory act?

A

the act of performing beyond the call of duty; the act of doing more than is necessary

81
Q

what is the percentage of different components of blood?

A
  • plasma = 55%
  • buffy coat = leukocytes and platelets (<1% of whole blood)
  • erythrocytes = 45%
82
Q

what is the lifespan of platelets?

A

9-10 days

83
Q

what are ‘blasts’ and where should they not be seen?

A

immature cells - should not be seen in circulation

84
Q

describe thrombopoiesis

A
  • Produces platelets
  • Process of endomitosis to produce megakaryoblasts (endomitosis is mitosis taking place without dissolution of the nuclear membrane and not followed by cytoplasmic division, resulting in doubling of the number of chromosomes within the nucleus)
  • Replication of chromosomes occurs but cells don’t divide (endomitotic replication)
  • Cells become larger and polyploid
  • Once fully mature, endomitosis ceases resulting in granulated cytoplasm
  • Process takes 2-3 days
  • Each megakaryocyte ‘fragments’ producing about 4000 platelets
  • Short life span so need a continuous production of platelets
  • megakaryoblast
  • promegakaryocyte
85
Q

how long do monocytes stay in circulation for? what is the shape of their nucleus?

A
  • 20-40 hours

- kidney shaped

86
Q

what is the effect of temperature of the affinity of haemoglobin to oxygen? why is this useful?

A

increased temperature -> decreased affinity -> shift to the right
- cooler in lungs than tissues = promotes uptake of oxygen

87
Q

what is the effect of 2,3-diphosphoglycerate? what is it?

A
  • metabolic compound present within red blood cells
  • increased 2,3-DPG -> decreased affinity -> shift to the right
  • so lower carrying capacity of oxygen in the blood
  • 2,3-DPG holds the haemoglobin in the tense state
88
Q

what is the affinity of myoglobin to oxygen like?

A
  • O2 saturation curve shifted to left
  • means for any given partial pressure, it has a greater affinity for oxygen
  • encourages the movement of oxygen from the blood into the muscle
89
Q

what are the changes in globin chains with development?

A
  • foetal haemoglobin has a slightly different configuration to adult haemoglobin
  • beta chains reach their greatest level after birth, so it’s the shift in the amount of foetal vs. beta haemoglobin that changes the oxygen affinity
90
Q

what is the process of compatibility testing?

A 
CROSSMATCH 
Donor RBCs (washed – removed any plasma) + patient serum
	No agglutination = compatible 
	Agglutination = incompatible
91
Q

what is the Kleihauer test?

A
  • A blood test used to measure the amount of foetal haemoglobin transferred from a foetus to a mother’s bloodstream
  • It’s usually performed on Rh-negative mothers to determine the required dose of Rho(D) immune globulin (Rhlg) to inhibit formation of Rh antibodies in the mother and prevent Rh disease in future Rh-positive children

Medicine Sem 2 (10 decks)

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