Physiology of blood cells and haematological terminology

Question 1

Summarise the origin of the blood cells

Answer 1

Blood cells of all types originate in the bone marrow
They are ultimately derived from multipotent haemopoietic stem cells
The multipotent stem cells gives rise to lymphoid stem cells and myeloid stem cells, from which red cells, granulocytes, monocytes and platelets are derived

all cell types derived from multipotent haematopoietic stem cells in bone marrow - which then form myeloid or lymphoid stem cells

Question 2

Outline the stem cell hierarchy

Answer 2

Multipotent lymphoid-myeloid stem cell is the ultimate cell- gives rise to myeloid and lymphoid lineages
Blood cell derivatives (RBCs, platelets) are derived from these two lineages

Question 3

What cells are derived from the multipotent myeloid precursor

Answer 3

Megakaryocytes
Granulocyte-Monocyte
Erythroid

Question 4

What cells are derived from the multipotent lymphoid precursor?

Answer 4

T cells
B cells
NK cells

Question 5

Describe the key characteristics of stem cells

Answer 5

Ability to self-renew and produce mature progeny
How is that achieved?
Ability to divide into two cells with different characteristics, one another stem cell and the other a cell capable of differentiating to mature progeny

Self-renewal is important- allows the bone marrow to continue functioning and producing blood cells throughout the entire life span.

Question 6

Summarise the pathway in the development of erythrocytes

Answer 6

The myeloid stem cell/precursor can give rise to a proerythroblast (earliest recognisable cell in erythrocyte lineage)
This in turn gives rise to erythroblasts and then erythrocytes or red cells

Question 7

What are some common features of blasts

Answer 7

They have a large nucleus and a small amount of cytoplasm
Will generate the mature cell
i.e erythroblasts will generate erythrocytes.

Question 8

Outline normal erythroid maturation

Answer 8

Multipotent myeloid stem cell- proerythroblast- Early, intermediate and late erythroblasts (all nucleated) — erythrocytes (enucleated)

On final step of differentiation- cytoplasm squeezed out of endothelium and into sinusoids- which are digested by macrophages

myeloid stem cell > proerythroblast > erythroblast (nucleated) > erythrocyte (have lost the nucleus) - each step in differentiation involves division to produce two cells; nucleus is excluded in final division and ingested by macrophage

Question 9

What is the term for the production of red blood cells and where does it take place

Answer 9

The process of producing red cells is called erythropoiesis
Normal erythropoiesis requires the presence of erythropoietin
Erythropoietin is synthesized mainly by the kidney, in response to hypoxia

Question 10

Describe the feedback cycle between the kidney and the bone marrow

Answer 10

Hypoxia and anaemia trigger the kidney to increase erythropoietin synthesis
This leads to increased bone marrow activity
Which in turn leads to a greater production of red blood cells- important in maximising oxygen delivery to the tissues.

Question 11

How does the colour of red cells change as they mature

Answer 11

When they are immature they are more blue/purple

As they mature they become pinker

Question 12

Describe the synthesis of erythropoietin (EPO)

Answer 12

§ Normal erythropoiesis requires erythropoietin which is mainly synthesised in the kidneys in response to HYPOXIA.
o 90% of erythropoietin from juxtatubular interstitial cells of the kidneys.
o 10% of erythropoietin from hepatocytes and interstitial cells of the liver

These cells then enter the capillaries to reach the bone marrow via the circulatory system

Question 13

Outline the key properties of red blood cells

Answer 13

The erythrocyte survives about 120 days in the blood stream
Its main function is oxygen transport
It also transports some carbon dioxide (but most is transported via the plasma)
Ultimately it is destroyed by phagocytic cells of the spleen (and also to a lesser extent by the liver and other cells in the reticulo-endothelial system)

Question 14

Which property of RBCs allows the potential for blood transfusions

Answer 14

Their long life span- can last a long time when stored in vitro at a low temperature and added with an anti-coagulant

Question 15

Describe the differentiation of multipotent haematopoietic stem cells into myeloblasts and monoblasts

Answer 15

The multipotent haemopoietic stem cell can also give rise to a myeloblast and a monoblast, which in turn give rise to granulocytes and monocytes
Cytokines such as G-CSF, M-CSF, GM-CSF and various interleukins are needed

Question 16

Which cytokines are important in the differentiation of myeloblasts to granulocytes and monocytes?

Answer 16

G-CSF, granulocyte colony-stimulating factor; GM-CSF, granulocyte-macrophage colony-stimulating factor; M-CSF, macrophage colony-stimulating factor

Analysed the maturation of these cells in tissue culture and these cytokines happened to stimulated the maturation of these specific cells.

Question 17

Outline normal granulocyte maturation

Answer 17

Myeloblast ( most primitive recognisable cell)
Promyeloblast (shows evidence of dividing down granulocyte pathway: primary granules, Golgi zone (clear area) and eccentric nucleus- more mature cell in pathway)
Myelocyte (smaller, secondary granules, can tell at this stage which granulocyte is produced (neutrophil, basophil or eosinophil)
Metamyelocyte (differs as it has an indented nucleus)
Band form (just change of shape in nucleus- arranges into band form)
Neutrophil (nucleus segments into lobules- same thing happens in eosinophil and basophil pathway)

2 cells produced until metamyelocyte- from here- any changes are simply just changes in the morphology of the nucleus.

Question 18

What is a key change to the chromatin upon maturation

Answer 18

The chromatin becomes more condensed with maturation

Initially very diffuse and full of active DNA

Question 19

Which cell is formed between the late erythrocyte and the mature erythrocyte

Answer 19

A polychromatic erythrocyte (earliest red cell to get out into circulation) - larger than mature cell and has a faint blue tinge (still has ribosomes in cytoplasm- for synthesis of Hb)- keeps going in circulating cell fro a few days after release from bone marrow
20% larger than mature erythrocytes.

Question 20

How else can we detect the presence of reticulocytes (immature erythrocytes)

Answer 20

Specific stain which reticulocytes takes up

Causes them to form a recticulum (network)- allowing them to be counted

Question 21

Describe the function of neutrophils

Answer 21

The neutrophil granulocyte survives 7–10 hours in the circulation before migrating to tissues (short life span here too)
Its main function is defence against infection; it phagocytoses and then kills micro-organisms
Can function in the blood to defend against bacteraemias

Question 22

Essentially, what is pus

Answer 22

A collection of dead neutrophils

Question 23

Describe the two pools of neutrophils

Answer 23

Circulating- in the middle of the blood vessels

Marginal - adherent to the endothelium of the capillaries

Question 24

Describe how the neutrophils enter the tissues

Answer 24

Adhesion and margination
Rolling
Diapedesis (actual process of travelling through endothelium)
Migration (chemotaxis) - in tissues towards inflammation- attraction to chemokines.
Phagocytosis

Question 25

What does the term granulocyte refer to

Answer 25

The 3 lineages (eosinophils, basophils and neutrophils)

Question 26

Describe the key properties of the eosinophils

Answer 26

A myeloblast can also give rise to eosinophil granulocytes The eosinophil spends less time in the circulation than does the neutrophil Its main function is defence against parasitic infection (releases granules which kill parasites) Red/Orange granules

Question 27

Describe the key property of the basophils

Answer 27

A myeloblast can also give rise to basophil granulocytes Basophils have a role in allergic responses Take up basic stain- why they appear purple Role in response to various infective stimuli

Question 28

Summarise the maturation pathway for monocytes

Answer 28

The myeloid stem cell can also give rise to monocyte precursors and thence monocytes Monocytes spend several days in the circulation Monoblasts- promonocytes- monocytes

Question 29

Describe the key properties of monocytes

Answer 29

Monocytes migrate to tissues where they develop into macrophages and other specialized cells that have a phagocytic and scavenging function (called histiocytes or macrophages inside tissue) Macrophages also store and release iron They have a kidney bean shaped nucleus (indented nucleus) They are large

Question 30

Describe how macrophages can store and release iron

Answer 30

Take up erythroblasts who have ejected their cytoplasm and nucleus into sinusoids Convert Fe to ferritin and store it as Hemosiderin Allowing iron to be released when it is needed (i.e during erythropoiesis)

Question 31

Summarise the maturation pathway of the platelets

Answer 31

The haemopoietic stem cell can also give rise to megakaryocytes and thence platelets Megakaryocytes large cell- produce platelets by fragmentations of the cytoplasm of the megakaryocytes Leaving a bare nucleus in the bone marrow to be destroyed.

Question 32

Describe the key properties of platelets

Answer 32

Platelets survive about 10 days in the circulation Platelets have a role in primary haemostasis (which block small breaks in blood vessels) Platelets contribute phospholipid, which promotes blood coagulation (secondary haemostasis)

Question 33

Describe the key properties of lymphocytes

Answer 33

The lymphoid stem cell gives rise to T cells, B cells and natural killer (NK) cells Lymphocytes recirculate to lymph nodes and other tissues and then back to the blood stream Intravascular life span is very variable - due to recirculation Re-join circulation from lymphatic duct High nuclear: cytoplasmic ratio

Question 34

Describe the importance of lymphocyte recirculation

Answer 34

Once they recognise the antigen in the tissue- can recirculate to clear the antigen throughout the body- aiding the body's defence.

Question 35

Why is terminology important in medicine

Answer 35

In haematology, specialised language is used to describe blood films and counts You need to know what the words mean and what the clinical significance might be

Question 36

Why may a lymphocyte have a granulated nucleus

Answer 36

NKC OR cytotoxic T lymphocyte cytotoxic granules to kill pathogen.

Question 37

Define Ansiocytosis

Answer 37

red cells show more variation in size than is normal

Question 38

Define Poikilocytosis

Answer 38

red cells show more variation in shape than is normal Could be due to an inherited haemolytic anaemia

Question 39

What is meant by microcytosis and macrocytosis

Answer 39

Microcytosis – red cells are smaller than normal Macrocytosis – red cells are larger than normal Microcyte – a red cell that is smaller than normal Macrocyte – a red cell that is larger than normal

Question 40

how can we determine whether a blood cell is microcytic or macrocytic

Answer 40

RBCs should roughly be equal in diameter to the nucleus of a lymphocyte We also have automated blood cell counters which measure the size of the RBCs

Question 41

Describe the different specific types of macrocytes

Answer 41

``` Macrocytes can be of specific types Round macrocytes Oval macrocytes (significant as common in VB12 or folic acid deficiency) Polychromatic macrocytes (lots of immature cells in circulation- could be responding to haemorrhage or deficient in vitamin administered i.e a previous deficiency but now administered vitamin) ``` Dependent on shape and staining characteristics upon blood film

Question 42

What do the terms microcytic, normocytic and macrocytic refer to

Answer 42

Microcytic – describes red cells that are smaller than normal or an anaemia with small red cells Normocytic – describes red cells that are of normal size or an anaemia with normal sized red cells Macrocytic – describes red cells that are larger than normal or an anaemia with large red cells

Question 43

Describe the normal central pallor of RBCs (hypochromia)

Answer 43

Normal red cells have about a third of the diameter that is pale This is a result of the disk shape of the red cell; the centre has less haemoglobin and is therefore paler

Question 44

Describe what is meant by hypochromia

Answer 44

Hypochromia means that the cells have a larger area of central pallor than normal This results from a lower haemoglobin content and concentration and a flatter cell Red cells that show hypochromia are described as hypochromic Hypochromia and microcytosis often go together (often due to Fe deficiency and thus the failure to synthesise Hb) 80-90% of RBC is pale (increased central pallor)

Question 45

Essentially, what happens in thalassaemia major

Answer 45

Defect in globin genes- can't synthesise Hb Will see blobs of Fe in cell- as the Fe is not incorporated with globin Cells will be hypochromic

Question 46

What is meant by hyperchromia

Answer 46

Hyperchromia means that cells lack central pallor This can occur because they are thicker than normal (macrocytes) or because their shape is abnormal Cells showing hyperchromia can be described as hyperchromatic or hyperchromic

Question 47

Describe adnormal cell shape as a cause of hyperchromia

Answer 47

Hyperchromia has many causes since many abnormally shaped cells lack the central thinner area However there are only two important types, spherocytes and irregularly contracted cells

Question 48

Describe spherocytes

Answer 48

Spherocytes are cells that are approximately spherical in shape They therefore have a round, regular outline and lack central pallor They result from the loss of cell membrane without the loss of an equivalent amount of cytoplasm so the cell is forced to round up and close whatever is left inside the membrane

Question 49

Describe hereditary spherocytosis

Answer 49

Spherocytes in hereditary spherocytosis – but not all the cells are spherical Inherited abnormality in RBC membrane- not tethered to the cytoskeleton- so the membrane is lost (BUT the cells start of as disc shaped then become more spherical as the membrane is lost)

Question 50

Describe irregularly contracted cells

Answer 50

Irregularly contracted cells are irregular in outline but are smaller than normal cells and have lost their central pallor They usually result from oxidant damage to the cell membrane and to the haemoglobin

Question 51

Describe some oxidants for Hb

Answer 51

Foreign chemical Food stuff (fava beans or broad beans) Strongly oxidant to Hb and RBCs- if RBCs lack the enzyme to metabolise them- can oxidise Hb and cause it to clump- forming irregularly contracted cells Causing a haemolyitic anaemia which would show these cells on a blood film

Question 52

What is meant by polychromasia

Answer 52

Polychromasia describes an increased blue tinge to the cytoplasm of a red cell It indicates that the red cell is young Cell is often much larger Normally leave bone marrow with a slight blue tinge But these cells have been released early in development and so still contain lots of ribosomes, causing the blue to be superimposed

Question 53

Describe the reticulocyte stain

Answer 53

Another way to detect young cells is to do a reticulocyte stain This exposes living red cells to new methylene blue, which precipitates as a network or ‘reticulum’ Cells which take up the stain can be counted and expressed as a % of the total cells (needs to look at 100s to get a precise and reliable estimate) Should only have 1-2% of these cells in the population circulating.

Question 54

How else can you identify reticulocytes

Answer 54

Detecting polychromasia or increased numbers of reticulocytes gives you similar information (although much harder to see tinges of blue- stain best) However, identification of reticulocytes is more reliable so they can be counted

Question 55

What is polychromasia an indication for

Answer 55

early release from bone marrow so many ribosomes - indication for subsequent reticulocyte count / stain

Question 56

List the different types of Poikilocytes

Answer 56

Spherocytes Irregularly contracted cells Sickle cells (crescent shaped with pointy ends) Target cells (blob of Hb in middle of cell- giving appearance of target) Elliptocytes (elliptical in shape- a bit fatter- ovalocyte) Fragments (small bit of RBCs often angular- often called schizocytes)

Question 57

Describe target cells

Answer 57

Target cells are cells with an accumulation of haemoglobin in the centre of the area of central pallor They occur in obstructive jaundice, liver disease, haemoglobinopathies and hyposplenism Also in haemoglobinopathies

Question 58

Describe elliptocytes

Answer 58

Elliptocytes are elliptical in shape | They occur in hereditary elliptocytosis and in iron deficiency

Question 59

On a blood film, how can you distinguish between eliptocytes in hereditary elliptocytosis and elliptocytes in iron deficiency

Answer 59

Iron deficiency blood film will also show hypochromic cells (including hypochromic elliptocytes- often called pencil cells) Also microcytic cells

Question 60

Describe sickle cells

Answer 60

Sickle cells are sickle or crescent shaped They result from the polymerisation of haemoglobin S when it is present in a high concentration Common in conditions of reduced oxygen tension

Question 61

Describe boat cells

Answer 61

Cells where HbS is polymerised but not to an extent to produce a sickle-shaped cell (but will soon become sickle-shaped) This gives the appearance of a boat-shaped cell If found on film- look around for sickle cells

Question 62

Describe fragments

Answer 62

Fragments or schistocytes are small pieces of red cells | They indicate that a red cell has fragmented

Question 63

Which two terms describe abnormalities in the relationship between different RBCs

Answer 63

Rouleaux | Agglutinates

Question 64

Describe Rouleaux

Answer 64

Rouleaux are stacks of red cells The resemble a pile of coins They result from alterations in plasma proteins

Question 65

Explain the different causes of Rouleaux

Answer 65

Normally RBC repel each other and will appear separated on the blood film However increased in high molecular weight plasma proteins such as Ig during infective and inflammatory states can negate these neutralising forces- causing Rouleaux.

Question 66

Describe agglutinates

Answer 66

Red cell agglutinates differ from rouleaux in that they are irregular clumps, rather than tidy stacks They usually result from antibody on the surface of the cells - which cause the RBCs to clump together

Question 67

What can RBCs sometime have

Answer 67

Inclusions (Howell-Jolly body)

Question 68

Describe Howell-Jolly bodies

Answer 68

A Howell‒Jolly body is a nuclear remnant in a red cell The commonest cause is lack of splenic function Produced in bone marrow but removed by spleen and so should not be seen in circulating blood Indicates that spleen isn't functioning (may have atrophied) OR spleen has been removed.

Question 69

What do the terms leucocytosis and leucopenia refer to

Answer 69

Leucocytosis — too many white cells | Leucopenia — too few white cells

Question 70

What do the terms neutrophilia and neutropenia refer to

Answer 70

Neutrophilia — too many neutrophils | Neutropenia — too few neutrophils

Question 71

What do the terms lymphocytosis and lymphopenia refer to

Answer 71

Lymphopenia: not enough lymphocytes | Lymphocytosis — too many lymphocytes

Question 72

What does the term eosinophilia refer to

Answer 72

too many eosinophils

Question 73

What do the terms thrombocytosis and thrombocytopenia refer to

Answer 73

Thrombocytosis: too many platelets Thrombocytopenia: too few

Question 74

What do the terms erythrocytosis and reticulocytosis refer to

Answer 74

Erythrocytosis: too many erythrocytes Reticulocytosis: too many reticulocytes

Question 75

What is the difference between a symptom and a sign

Answer 75

Symptom- what the patient tells you about (often how they feel) Sign- what you see on examination (i.e pallor)

Question 76

Describe atypical lymphocytes

Answer 76

An atypical lymphocyte is an abnormal lymphocyte Often the term is used to describe the abnormal cells present in infectious mononucleosis (‘glandular fever’) ‘Atypical mononuclear cell’ is an alternative term Often develop in response to infections- but mostly viral infections. An atypical lymphocyte will have a large nucleus and a large amount of faint cytoplasm

Question 77

What is meant by left shift

Answer 77

Left shift means that there is an increase in non-segmented neutrophils or that there are neutrophil precursors in the blood An increase in non-segmented neutrophils More band forms or promyelocytes e.g Sign of infection or inflammation (will see heavy granules and vacuoles in band forms which indicate infection) band cells with no segmentation indicate rapid production during infection May also see neutrophilia and therefore also leucocytosis.

Question 78

Describe right shift

Answer 78

Hyper-segmented nuclei in neutrophil

Question 79

Describe toxic granulation

Answer 79

Toxic granulation is heavy granulation of neutrophils It results from infection, inflammation and tissue necrosis (but is also a normal feature of pregnancy) May see heavy granules and vacuoles if infection

Question 80

Describe hypersegmented neutrophils (right shift)

Answer 80

Neutrophil hypersegmentation means that there is an increase in the average number of neutrophil lobes or segments (should normally see 3/4- but in right shift may see >6) It usually results from a lack of vitamin B12 or folic acid

Question 81

How can you look for anaemia on a blood film

Answer 81

How thin the blood spreads depends on its viscosity If anaemic- low viscosity Thin film More spaces between cells

Question 82

How can sickle cell anaemia lead to the presence of Howell-Jolly bodies

Answer 82

Infarction of spleen- therefore nuclear remanants not removed.

Question 83

Describe tear drop cells

Answer 83

Dacrocytes