"Blood" - what is it, definition of the term
The circulatory fluid of mammals, consisting of plasma, erythrocytes, leukocytes, and platelets, transports oxygen, nutrients, hormones, and metabolic waste throughout the organism. In rodents such as rats and mice, this red liquid originates in the bone marrow where hematopoietic stem cells differentiate into the various cellular components. Plasma, a water‑based solution containing proteins, electrolytes, and metabolites, serves as the transport medium, while the cellular fraction performs gas exchange, immune defense, and hemostasis. The fluid circulates through a closed vascular network driven by cardiac contractions, maintaining tissue perfusion and homeostasis.
Detailed information
The circulatory fluid of rodents consists of plasma, red blood cells, white blood cells, and platelets. Plasma accounts for roughly 55 % of the total volume and contains water, electrolytes, proteins (albumin, globulins, fibrinogen), hormones, and metabolic waste. Red blood cells, which represent about 40–45 % of the fluid, carry hemoglobin for oxygen transport; typical mouse values are 12–15 g/dL hemoglobin and a hematocrit of 40–45 %, while rats show slightly higher ranges of 13–16 g/dL and 45–50 % hematocrit. White blood cells comprise less than 1 % of the volume; normal counts are 2–5 × 10⁹/L in mice and 3–6 × 10⁹/L in rats. Platelets are present at 600–1000 × 10⁹/L in mice and 800–1500 × 10⁹/L in rats.
Key physiological differences include:
- Size of erythrocytes: mouse cells average 5–6 µm in diameter, rat cells 6–7 µm.
- Lifespan: red cells survive approximately 30 days in mice and 45 days in rats.
- Viscosity: plasma viscosity is marginally higher in rats due to greater protein concentration.
Sampling techniques prioritize minimal stress and volume control. Common methods are:
- Retro-orbital sinus puncture (max 0.2 mL per collection, suitable for mice).
- Tail vein or saphenous vein phlebotomy (0.1–0.3 mL, applicable to both species).
- Cardiac puncture under anesthesia (up to 1 mL, terminal procedure).
Anticoagulants used include heparin for biochemical assays and EDTA for hematology. Storage guidelines specify refrigeration at 2–8 °C for up to 24 hours; freezing plasma at –80 °C preserves protein integrity for longer periods.
Analytical standards:
- Complete blood count: automated hematology analyzers calibrated for small rodent volumes provide accurate leukocyte differentials.
- Hemoglobin concentration: cyanmethemoglobin method or spectrophotometric analysis yields precise measurements.
- Plasma chemistry: enzymatic kits assess glucose, urea, creatinine, and electrolyte levels, with reference ranges adjusted for species-specific metabolism.
Understanding these parameters supports experimental design, disease modeling, and pharmacological testing in laboratory rodents.