Hematopoietic System

Clinical Pathology

Hematopoietic System

• Blood supplies cells with water, nutrients, electrolytes, and hormone. • Removes waste products

• Mainly CO2

• Cellular elements supply oxygen (RBC), protect against foreign organisms (WBC) and initiate coagulation (platelets).• Clotting factors

Hemoglobin

• Normal values are usually 1/3 of the hematocrit.• Each hemoglobin molecule has 4 heme units

attached to globulins.• Abnormal heme groups, cannot carry oxygen.• Carboxyhemaglobin- Hgb has a higher affinity for

CO than O2.

• Bright red blood• Methemoglobin- The Fe molecule is oxidized to

Fe+3.• Blood becomes brown.• Tylenol toxicity in cats.

Hemoglobin Molecule

Oxygen-Hemoglobin Dissociation Curve

• Increasing the temperature denatures the bond between hemoglobin and oxygen.

• A decrease in pH causes a shift to the right causing more O2 to be released.

• Organic phosphates decrease the affinity of hemoglobin to O2.

• The purpose of the curve is to show the equilibrium of oxyhemoglobin at various partial pressures.

• At high partial pressures of oxygen, usually in lungs, hemoglobin binds to oxygen.

Red Blood Cells

• Function:• Carry oxygen to the tissues• Oxygen must be carried at enough

pressure to permit rapid diffusion of oxygen.

• The RBC is a vehicle for hemoglobin which is the carrier molecule for oxygen.

• The sigmoid shape of curve is a result of the cooperative binding from the 4 hemoglobin molecules.

Transport of oxygen in the blood

• 97% of oxygen transported from lungs to the tissues is carried in chemical combination with hemoglobin in RBC’s.

• When the Po2, is high, O2 binds to hemoglobin. When Po2 is low, O2 is released.

Erythropoiesis

• Maturation of a RBC.• Only occurs in the bone marrow of normal

adult animals.• Occurs in the spleen and liver of the

fetus.• Maturation time usually takes 5 days.• Regulated by erythropoietin (EPO) which

is increased in the presence of hypoxia.• In most species, the kidney is the sensor

organ and major site of EPO.

Red Blood Cells (Erythrocytes)

• No nucleus due to have to fold and squeeze through tight spaces.

• Normocytes- cells look normal

Erythrocyte Life Span

• Dog- 110 days• Cat- 70 days• Cow- 160 days• Horse- 145 days• Man- 120 days• Mouse- 30 days

Erythrocyte Life Span

• Stem Cell → Rubriblast → Prorubricyte → Metarubricyte → Rubricyte → Reticulocyte → RBC

• Rubricyte- nucleated RBC releases in severe anemia.• No more mitotic division takes place

after this stage.• One rubriblast may give rise to as many as

8-32 RBC’s.

Reticulocytes in the Peripheral Blood

• Non-nucleated cell containing RNA which can be easily seen when stained with methylene blue.

• Hallmark of erythrocyte regenerative response.

Polychromasia

• Show a faint, bluish tint. These cells would appear to be reticulocytes if stained with methylene blue.

Nucleated Erythrocytes

• Metarubricytes are sometimes found in the peripheral blood.

• Usually observed with regenerative anemias.

• May be found in non-regenerative states such as lead poisoning and hypoxia.

Macrocytosis

• Erythrocytes are larger than normal. • Usually in the presence of regenerative

anemia.• May be seen in FeLv infected cats.• Anisocytosis- increase variation of the

size.

Microcytosis

• Cells are smaller than normal which has been determined by the Mean Cell Volume (MCV).

• A decreased MCV suggests that the cells are smaller than normal.

• Usually occurs with iron deficiency cause by chronic blood loss or parasitism.• Haemobartonella• Feline Leukemia

Hypochromasia

• RBC’s that have decreased density of the characteristic hemoglobin color.

• Frequently observed in iron deficiency anemia caused by chronic blood los or parasitism.

Howell-Jolly Bodies

• Nuclear remnants observed in young erythrocytes.• Often observed in cats and horses.• Can be seen in regenerative anemic animals.• Also may be seen with splenic disease or in an animal

with the spleen removed.

Basophilic Stippling

• Observed in RBC’s that contain abnormal aggregation of RNA.

• Can be observed in cases of heavy metal poisoning with non-regenerative anemias or intense erythrogenesis in dogs, cats, and ruminants.

Spherocytes

• Cells have a spheroid shape instead of the usual biconcave disk shape.

• Have reduced cell membrane and are hypochromatic.

• Seen most frequently in autoimmune hemolytic anemia (AIHA).

• Usually seen in dogs.

Heinz Bodies

• Particles of denature hemoglobin protien.• They stain with new methylene blue and appear as

colorless bumps with quick stain.• May be caused by oxidant drugs and chemicals.• Normal cat blood may have 2-3%.• Spleen recognizes as abnormal and starts to lyse

the cells.

Crenation

• Identified as the presence of many irregular membrane projections involving most RBC’s.

• It is usually an artifact due to slow drying of the blood film.

• Commonly observed in pig blood but can be seen in any species.

Schistocytes

• Also known as poikilocytes.• RBC’s with abnormal shape.• They are observed in fragmentation hemolysis caused by

DIC, vascular neoplasia, endocarditis, and possibly iron deficiency anemia.

Target Cells and Folded Cells

• Two types of leptocytes observed mainly in dogs.

• Represent cells with an increases membrane-to-volume ratio not specific to any disease.

• The cell membrane is thin and flimsy.

Rouleaux• RBC’s that in the form of stack

of coins that has ben pushed over.

• Commonly observed in horses and sometimes cats.

• May indicate increase immunoglobulins in other species.• Autoimmune disease

Autoagglutination

• Irregular clumping together of RBC’s caused by presence of anti-red cell antibody.

Normal Canine Blood

Normal Feline Blood

• Feline RBC’s have less central pallor compared to canine blood.

• Rouleaux and crenation are common features.

Normal Equine Blood

• RBC’s have little central pallor and rouleaux is normal.

Normal Bovine Blood

• RBC’s are often crenated.• Anisocytosis is sometimes observed in

normal blood.

Platelets

• Form the initial hemostatic plug whenever hemorrhage occurs.

• The source of phospholipid which is needed for coagulation factors to interact to form a fibrin clot.

• Produced in the bone marrow by megakaryocytes under the influence of thrombopoietin.

Laboratory Evaluation on Blood

• CBC- Complete Blood Count• Involves:

• Quantifying numbers of RBC’s , WBC’s, and platelets.

• Making qualitative comments on cell morphology.

• Determining the plasma protein level and color.

Blood Evaluation

• Hematocrit- the % of RBC to plasma. Acquired by centrifuging blood in a microhematocrit tube for 5 minutes and then read.

• Hemoglobin- 1/3 the hematocrit.• Red cell count- usually in the 5-15 x 106 ul

range.

Instrumentation

• Electronic cell counters- based on the principle that cells are poor electrical conductors. A measured volume of diluted blood is drawn between two electrodes, causing a resistance in an electrical current.

• QBC- quantitative buffy coat system, utilizes differential centrifugation and quantification of cellular elements in a specialized microhematocrit tube.

Manual Procedures

• Packed Cell Volume (PCV aka hematocrit)- % of RBC’s in the blood.

• White Blood Cell Count- use of a hematocytometer and microscope involves observing the blood and counting the number of cells.

• Evaluation of blood films- feathering technique of a drop of blood on a slide then staining before examining with a microscop.