Introduction to Blood

Question 1

List the qualities of blood that allows it to provide a means for sampling body tissues and fluids.

Answer 1

It is largely homogenous
It is in equilibrium with tissues
Shows reactive responses in disease states

Question 2

List the components of blood.

Answer 2

Blood cells
Plasma proteins
Products of metabolism - metabolites, hormones etc.
Leakage from tissue cells - enzymes, other cytoplasmic constituents
May contain pathogens

Question 3

What is haematology concerned with?

Answer 3

Cells of the blood

Haemostasis - control of bleeding & clotting

Question 4

Name what the haematology laboratory assessment of blood cells involves.

Answer 4

Cell counts - quantitative
- red cells: concentration, size, contents
- leucocytes: concentration
Blood film examination to:
- check morphology - qualitative evaluation
- confirm cell count data - quantitative check
Specialized tests

Question 5

Name the normal lecuocytes and reticulocytes.

Answer 5

Band forms and melanocytes
Neutrophil 
Eosinophil 
Basophil 
Monocyte
Lymphocyte 
Reticulocytes

Question 6

What is the purpose of an Automated Haematology Analyser?

Answer 6

Provides an automated count of cells

Single cells assessed by laser beam (cell size, cytoplasmic/nuclear activity, detection of peroxidase enzyme)

Question 7

Name the parameters of RBCs that are usually examined.

Answer 7

Red cell concentration (RBC)
Haemoglobin (Hb)
Haematocrit (Hct) 
Mean cell volume (MCV)
Mean cell Hb (MCH) 
(Mean cell Hb conc.)

Question 8

Define reference range/interval for a population.

Answer 8

The range of values present in 95% of healthy individuals of a specified population, for a test.

Question 9

Name the factors affecting reference ranges for blood cells.

Answer 9

Developmental age
Gender
Psychological changes - pregnancy, high altitude, climate
Ethnic (genetic) differences

Question 10

Define anaemia.

Answer 10

Reduced haemoglobin for age, gender, geography/ethnicity.

Indicates reduced ability to transport oxygen in blood

Question 11

Name the different cell size types relating to anemia.

Answer 11

Microcytic
Macrocytic
Normocytic

Question 12

Name the different cell concentrations of Hb relating to anaemia.

Answer 12

Hypochromic

Normochromic

Question 13

Define microcytic hypochromic anaemia.

Answer 13

Small under filled red cells

Question 14

Define normochromic normocytic anaemia.

Answer 14

Normal red cells

Question 15

Define macrocytic anaemia (normochromic).

Answer 15

Large red cells

Question 16

Name features of microcytic hypochromic anaemia.

Answer 16

Iron Deficiency
Pencil cells and target cells
Erythroblasts show reduced Hb production & no stainable iron in marrow = no stores.
Early response to treatment of iron deficiency - some well-filled RBCs are present

Question 17

Why is MCHC not usually reported?

Answer 17

High level of error in calculated data.

Question 18

Discuss the features of normocytic normochromic anaemia.

Answer 18

Largest group of anaemias - common
Causes:
- Haemodilution occurring after acute blood loss
- Chronic or persistent inflammation or infection (mechanism - reduced normal red cell production)
- Renal failure
- Usually a secondary feature of an underlying disorder

Question 19

Name the features of macrocytic anaemia.

Answer 19

Common in liver disease
Megaloblastic anaemia is an important cause:
- caused by deficiency of vitamins needed for nucleic acid metabolism (folic acid/vit B12)
Delayed and abnormal maturation in marrow:
- many dividing cells die due to DNA errors caused by lack of nucleotides
- affects all tissues but blood abnormalities are usual means for diagnosis

Question 20

What is haemopoiesis?

Answer 20

Production of blood cells

Question 21

Where does haemopoiesis occur in fetuses?

Answer 21

Liver and spleen in vascular sinuses

Bone marrow - as bones develop

Question 22

Where does haemopoiesis occur in children?

Answer 22

Bone marrow - progressive loss from limb bones

Question 23

Where does haemopoiesis occur in adults?

Answer 23

Bone marrow - axial skeleton mainly (skull, vertebrae, ribs, sternum, coccyx)

Question 24

Name and describe the different types of stem cells.

Answer 24

Totipotent stem cells - embryonic development, can form any tissue
Pluripotent stem cells - increasing specialization to produce a limited range cell types
Adult stem cells (progenitor cells) - present in marrow, low numbers in blood, may be able to enter other tissues & participate in healing
Committed stem cells - myeloid, lymphoid cell lineages

Question 25

What are the key issues surrounding erythroblasts?

Answer 25

Proliferation
Iron uptake
Haemoglobin production
Removal of mitochondria, ER, ribosomes, golgi, loss of nucleus

Question 26

Name the control mechanisms surrounding regulation of haemopoiesis.

Answer 26

Cytokine signals - induce growth and differentiation, produced by peripheral tissues & cells of marrow
Marrow stromal cells - cell surface signals

Question 27

What is the result of haemopoiesis? Describe how it is an integrated process.

Answer 27

Results in self renewal of pluripotent stem cells 
Differentiation of some pluripotent stem cells into specific cell lineages = irreversible 
Feedback signals (cytokines/growth factors) from peripheral tissues provide important regulatory control.

Question 28

What type of cells do the regulatory signals in haemopoiesis act on?

Answer 28

Stromal cells - IL-1, TNF
Pluripotent stem cells - stem cell factor (SCF), Flt ligand
Multipotential progenitor cells - IL-3, GM-CSF, G-CSF, IL-6, TPO
Act on committed progenitor cells - G-CSF, M-CSF, IL-5, Erythropoietin, Thrombopoietin

Question 29

List and describe the committed cells of erythropoiesis.

Answer 29

Proerythroblast
Basophilic erythroblast (rapid division, iron uptake)
Polychromatic erythroblast (divides, Hb synthesized, then starts clearing RNA, mitochondria etc. and buds off nucleus to become a ….)
Reticulocyte (immature red cell, completes clearance of RNA, mitochondria, golgi. Migrates into blood 1-2 days)
Erythrocyte - 120 days

Question 30

How many red cells are produced each day by an average adult?

Answer 30

2-3 x 10^11

Question 31

Name the difference between an erythroblast and erythrocyte.

Answer 31

Erythroblast = nucleated cell
Erythrocyte = nucleus is discarded

Question 32

Name the flow characteristics of blood.

Answer 32

Viscosity - cells suspended in plasma
Red cells larger than some capillaries - elastic deformation to pass through capillaries
Flow characteristics in microvasculature (small arteries and arterioles, small veins and venules) - axial streaming of red cells, platelet rich plasma zone at periphery