Blood is a refined biological fluid essential for life.
Erythrocytes (Red Blood Cells):
Highly specialized for the transport of oxygen.
Lose their nucleus to maximize oxygen-carrying capacity.
Play a crucial role in managing carbon dioxide levels in the body.
THE RED BLOOD CELL (RBC)
Structure:
Biconcave disc shape.
Red coloration due to hemoglobin, which binds oxygen.
Function:
Transport oxygen to tissues and carbon dioxide away from tissues.
Characteristics:
In healthy circulation (specifically in dogs and cats), should not have a nucleus.
Production occurs in the Red Bone Marrow, primarily found at the ends of long bones.
If nucleated RBCs are found, this indicates they were released prematurely due to factors like stress or poor health.
ERYTHROPOIESIS
Definition:
The production of erythrocytes (RBCs).
Control Mechanism:
Regulated by a hormone called erythropoietin (EPO) produced in the kidneys.
EPO is released in response to hypoxia (low oxygen levels) detected by the kidneys.
Increases the production of RBCs when oxygen levels are low.
THE POIETINS
Overview:
Poietins are hormones or factors influencing the development of blood cells from multipotent stem cells.
Types include:
Leukopoietins: Stimulate white blood cell (WBC) production (Leukopoiesis).
Erythropoietin (EPO): Stimulates RBC production (Erythropoiesis).
Thrombopoietin: Stimulates platelet production (Thrombopoiesis).
EPO specifically assists stem cells in the marrow to mature into reticulocytes, which are immature RBCs that finalize their formation quickly in circulation.
ERYTHROPOIETIN (EPO)
Function:
Stimulates bone marrow stem cells to develop into reticulocytes.
Increases RBC production rates, maintaining homeostasis during stress, such as trauma.
MEASUREMENTS OF RBCs (CBC)
Complete Blood Count (CBC) evaluates various characteristics:
RBC Count
Hematocrit (HCT) / Packed Cell Volume (PCV)
Mean Corpuscular Volume (MCV)
Mean Corpuscular Hemoglobin (MCH)
Mean Corpuscular Hemoglobin Concentration (MCHC)
Red Cell Distribution Width (RDW)
Reticulocyte Count (RC)
Each parameter helps assess the overall status of erythrocytes in circulation.
ERYTHROCYTE MATURATION SEQUENCE
Sequence of stages during RBC development:
Rubriblast (youngest stage)
Prorubricyte
Rubricytes (early and late stages)
Metarubricyte
Polychromatophilic cell (often referred to as a reticulocyte or "Retic")
Mature RBC
RETICULOCYTE (POLYCHROMATIC CELL)
Characteristics:
Larger and bluer than mature RBCs due to RNA presence.
Lacks a nucleus, indicating its maturity.
Requires special staining (New Methylene Blue) for identification.
Normal Presence:
Typically 1-2% of total RBCs in dogs and cats.
Significant presence in cases of anemia, indicating regenerative capacity of the bone marrow.
Maturation Process:
Takes place within 24 hours of arriving in peripheral blood.
RETICULOCYTE RESPONSE TO ANEMIA
In conditions of anemia or hypoxia, reticulocytes are released at an increased rate, serving as a diagnostic indicator of bone marrow responsiveness and RBC regeneration potential.
For example, cows and horses typically do not see reticulocytes in circulation as maturation occurs entirely within the bone marrow.
RBC LIFE SPAN
Lifespan in various species:
Dog: 120 days
Cat: 70 days
Cow: 160 days
Horse: 145 days
RBC STRUCTURE
Components:
Hemoglobin:
Crucial protein for oxygen transport.
Contains four iron atoms, each capable of binding one oxygen molecule; thus, a single hemoglobin can carry four oxygen molecules.
Average RBC contains approximately 270 million hemoglobin molecules.
Cell Membrane:
Must be flexible to allow passage through small vessels (e.g., capillaries).
Importance of Structure:
Biconcave shape maximizes surface area to volume ratio, enhancing oxygen delivery efficiency.
Homeostasis maintained through sodium pumps in the membrane to prevent cell lysis.
RBCs IN CIRCULATION
Normally, red cells do not aggregate, allowing efficient oxygen delivery.
Negative charge on the membrane leads to zeta potential, which prevents clumping.
Inflammatory responses can reduce zeta potential, causing rouleaux (stacking of RBCs) formation.
Rouleaux Formation:
Can be a normal finding in certain species but excessive presence is abnormal, indicating underlying disease.
CIRCULATING RBC AGGLUTINATION CONDITIONS
Rouleaux vs. Agglutination:
Rouleaux: Stacking formation due to decreased zeta potential, can indicate inflammation.
Agglutination: Clumping due to autoimmune diseases or other triggers.
RBC DEATH AND BREAKDOWN
Through phagocytosis in the spleen, aged RBCs are broken down, leading to:
Heme breakdown into bilirubin, which contributes to jaundice.
Iron recycling via transferrin back to the marrow for new hemoglobin production.
BILIRUBIN METABOLISM
Major Waste Product:
Free (unconjugated) bilirubin binds with albumin, transported to the liver, where it converts to conjugated bilirubin (water-soluble).
Excretion via bile, primarily in feces, and some is presented in urine as urobilinogen.
Abnormal breakdown leads to elevated bilirubin levels in blood, causing icterus or jaundice.
RBC INCLUSIONS
Howell-Jolly Bodies:
Nuclear remnants present in RBCs, common in regeneration.
Heinz Bodies:
Denatured hemoglobin present due to oxidative damage; more common in cats due to their susceptibility.
Mycoplasma:
Intracellular parasites that require careful examination.
EXAMINATION OF RBC MORPHOLOGY
Characteristics to assess:
Size: Microcytic or macrocytic findings.
Color: Polychromatic, hypochromic, or hyperchromic indicators.
Shape: Presence of poikilocytosis and specific formations such as spherocytes and acanthocytes.
Inclusions: Any abnormal presence indicating pathology.
LABORATORY EVALUATION OF RBCs
Manual tests (spun hematocrit) and automated tests provide key indications about health status related to erythrocytes.
Key Ratios: MCV, MCH, MCHC must be calculated to understand cellular performance and to diagnose anemia effectively.
These measures allow differentiation between types of anemia, such as regenerative versus non-regenerative anemias.