Introduction to Haematology System, Constituents of Blood and Haemopoiesis

Question 1

Define what blood is

Answer 1

Blood is a specialized fluid (technically a tissue) composed of cells suspended in a liquid (plasma)

Question 2

What are the 3 different types of blood cells ?

Answer 2

1. RBC’s
2. WBC’s
3. Platelets

Question 3

In very general terms why do we need each of the 3 different types of blood cells ?

Answer 3

1. RBC’s to carry oxygen
2. WBC’s to fight infection
3. Platelets to prevent bleeding

Question 4

What is the production of blood cells (talking about all 3 types of blood cells) termed and what are blood cells formed from ?

Answer 4

• The production of blood cells is termed haemopoiesis or haematopoesis
• Blood cells are produced froma relatively small pool of pluripotent stem cells capable of making all the different types of blood cells

Question 5

What are the sites for haematopoeisis in an adult ?

Answer 5

Bone marrow of skull, ribs sternum, pelvis, proximal ends of femur (generally more the axial skeleton i.e. head and trunk)

Question 6

Other than the bone marrow what are the 2 other sites where blood cells can be produced (note they arent usually produced here in adults and can be associated with pathologies if they are producing blood cells)

Answer 6

Liver and spleen

Question 7

Appreciate that huge numbers of blood cell production is required to maintain the status quo:

Approximately:

• 100 million red cells/minute
• 60 million neutrophils/minute
• 150 million platelets/minute

Question 8

What has to happen to a stem cell to produce blood cells ?

Answer 8

They have to proliferate (increase in numbers) and differentiate (development of the features of the specialised end cell from the stem cell)

Basically they go down the haematopoietic tree and as they do they increase in the number of cells at each level becuase they are dividing and at each stage they develop more characteristics of the specialised end cell

Question 9

Go over this pic of the haematopoietic tree (dont need to learn it all just have a rough idea)

• LT-HSC = long term haematopoietic stem cell
• ST = short term

Question 10

Appreicate that stem cells do not proliferate often and they are morphologically unremarkable (cant be distinguished based on morphology)

Question 11

What state are most stem cells in ?

Answer 11

A state of quiescent i.e. period of inactivity or dormancy

Question 12

What is the earliest morphologically identifiable precursor of neutrophils and what go over the pic for the stages of neutrophil development?

Answer 12

Myeloblasts

Question 13

What are the earliest morphological precursors of erythrocytes ?

Also have a look at the development of erythroblasts just appreicate it and have a rough idea

Answer 13

Pronormoblasts

Question 14

In general what happens to the size of cells as the go down the developmental tree?

Answer 14

They become smaller

Question 15

What are the main changes occuring to pecursor cells in the bone marrow (that is the precursor cells upto just before reticulocytes) to erythrocytes, going down the developmental pathway ?

Answer 15

1. There nucleus’s become more condensed (eventually lost)
2. The progressively contain less RNA and more Hb

Question 16

What is the key thing that happens in the formation of a recticulocyte ?

Answer 16

The nucleus is lost forming a recticulocyte

Question 17

What is the difference between recticulocytes and erythrocytes ?

Answer 17

Both have lost their nucleus, but recticulocytes stain very slightly blue because they still have a small amount of RNA, they then loose this RNA and some cell volume to form erythrocytes

Question 18

What is the difference in location of recticulocytes and erythrocytes compared to the other precursor cells ?

Answer 18

• They are found in the blood whereas the other cells are normally found in the bone marrow
• Note that recticulocytes are also present in the bone marrow just before moving out into the blood

Question 19

What are the main types of WBC’s (include the subtypes if that type has them)

Answer 19

• Graulocytes ==> neutrophils, basophils and eosinophils
• Monocytes (macrophages)
• Lymphocytes ==> B cells, T cells and NK cells

Question 20

Why are eosinophils, neutrophils, basophils all collectively termed granulocytes ?

Answer 20

Becuase they contain granules that are easily visible on light microscopy

Question 21

What type of cell is shown and what are the characterisitc features of it ?

Answer 21

Neutrophil:

• Segmented nucleus (polymorph) (usually 2-5 lobes)
• Neutral (pH) staining granules

Question 22

What is the function of neutrophils ?

Answer 22

They are attracted to sites of infection or inflamation

• Phagocytose invaders (bacteria and fungi), and damaged cells
• Kill with granule contents and die in the process - hydrogen perioxide produced by myeloperoxidase contained in granules
• Attract other cells

Question 23

Are neutrophils counts only raised in response to infection?

Answer 23

No - also trauma and infarction (think back to their function of phagocytosing damaged cells)

Question 24

Do neutrophils remain in the blood circulation for long ?

Answer 24

No - they have a short life in the circulation and transit to the tissues