Haematology 1 Flashcards
THE ORIGINS OF BLOOD CELLS. -Basic lifecycle of blood cells. -Terminology. -Main abnormalities seen in haematology and general approach to investigation. -Species differences.
HAEMATOPOEITIC TISSUE
In the embryo- Yolk sac.
Foetus- Liver and spleen. EXTRAMEDULLARY.
Adult- Bone marrow, although the haematopoetic abilities of the liver and spleen remain.
BONE MARROW
There is much red marrow in young animals. This is actively producing blood cells; there is a high demand for blood cells.
Older animals have less demand for blood cells, so there is less red marrow.
The red marrow that remains is mostly seen in the flat bones and at the ends of long bones.
Yellow marrow contains fat and supporting cells.
It can transform back to red marrow if necessary.
ERYTHROPOEISIS
Red blood cell formation.
- > Multipotential stem cell
- > Unipotential stem cell
- > Rubriblast/proerythroblast- FIRST RECOGNISABLE CELLS
- > Prorubricyte/basophilic erythroblast/early normoblast
- > Rubricyte/polychromatophilic erythroblast
- > Metarubricyte/orthochromatic erythroblast/late normoblast
- > Reticulocyte- Occasionally seen in blood.
- > Erythrocyte- Seen in blood.
Cells and nuclei get smaller as erythropoeisis progresses.
WHAT STAIN SHOULD BE USED FOR RETICULOCYTES?
NEW METHYLENE BLUE.
Supravital stain- stain and cells are mised together.
Often used in anaemia to see if marrow is responding.
Reticulocyte organs are precipitated and appear as DARK GRANULES.
LIFE OF AN ERYTHROCYTE
Spends around 5 days in bone marrow, from stem cell to reticulocyte.
2 days- ABSOLUTE MATURATION from reticulocyte to erythrocyte.
Lifespan average 100 days.
Aged red blood cells travel to the SPLEEN, where they are processed by macrophages and iron is recycled (for use in new blood cells)
Bilirubin passes to the liver via albumin transport protein.
It is conjugated to make in water soluble.
This allows Phase II excretion (in bile).
SPLENIC SEQUESTRATION
Red blood cells are stored in the spleen.
Seen in DOGS and HORSES.
Splenic contraction on stress means that and increase (excessive) erythrocytes can be seen- erythrocytosis.
This is a transient effect, lasting for ~30 minutes.
ERYTHROPOETIN
An hormone produced by the kidneys.
Kidney disease can affect EPO production (eg. chronic kidney disease causes decreased EPO production).
EPO stimulates red cell production by stimulating proliferation of erythrocyte progenitors.
The fundamental stimulus of EPO release is HYPOXIA.
GRANULOPOEISIS
Whote blood cell formation.
- > Multipotential stem cell
- > Unipotential stem cell
- > Myeloblast- FIRST RECOGNISABLE CELL
- > Promyelocyte
- > Myelocyte (specific granulation is seen)
- > Metamyelocyte
- > Band neutrophils
- > Mature/segmented neutrophils- seen in storage pool.
Neutrophils are released in to the blood when signalled.
LIFE OF A GRANULOCYTE
Spends around 6 days maturing in bone marrow before release in to blood as circulating neutrophil.
Blood neutrophils are divided in to 2 pools:
1. CIRCULATING NEUTROPHILS
2. MARGINATING NEUTROPHILS
Circulating neutrophils are present in the central axial blood flow, so are the cells seen on blood samples.
Marginating neutrophils are seen on the endothelial lining of blood vessels, waiting for a signal to undergo diapedesis- they are NOT seen on blood samples.
Once neutrophils migrate to tissues, they do not return back to blood.
They are either lost from body surfaces, or destroyed by macrophages.
OTHER LEUKOCYTES
EOSINOPHILS- take 2-6 days to develop in bone marrow.
Then spend 1-24 hours in circulation.
Exit to tissue (skin, GI tract, respiratory).
Last for 2 days to 2 weeks.
MONOCYTES- Short transit time in blood.
Are recruited in to tissues, where they differentiate in to macrophages.
Lifespan variable.
SPECIES DIFFERENCES
KNOW THESE! Species differences can confuse software.
-Red cell size: DOGS > HORSES > CATS > RUMINANTS
-Horses do NOT release immature red blood cells (reticulocytes) from the bone marrow. Circulating reticulocytes should NOT be seen.
-ROULEAUX FORMATION- NORMAL in horses, seen in inflammation in cats.
Occurs due to increased viscosity overwhelming the small negative charge on erythrocytes.
-Breed differences- sight hounds often have a high PCV due to lots of erythrocytes.
- warm vs coldblooded horses have differences in reference intervals. Seasonal variations are also seen.
RABBITS
Reticulocytes are a normal feature in circulating blood.
This is due to the high turnover of erythrocytes and the short lifespan (of animal?)
BIRDS/FISH/REPTILES
have NUCLEATED red blood cells.
Platelets have ragged edged cytoplasm.
Heterophils are equivalent to neutrophils.
BLOOD ANALYSIS
Centrifuged haematocrit plus smear- most basic, but gives good information.
Look at all cell parameters from machine analysis (RDW not often looked at unless there are many differences in red cell width).
Be aware of ‘normal’ REFERENCE INTERVALS (vary between lab/animal population/species)
95% representative, but 5% unrepresented- age/breed differences.
SMEAR REPORT is very important to verify analysis figures/identify artefacts/morphological changes.
