Blood composition and basic hematology notes

Blood composition

  • Blood is a specialized connective tissue made of plasma (the liquid) plus formed elements (red cells, white cells, platelets) that transport gases, nutrients, immune cells, and clotting factors throughout the body.
  • Blood composition
    • Plasma (approx. ∼55%\sim 55\% of blood volume): watery solution with proteins, electrolytes, nutrients, hormones, and waste.
    • Formed elements (approx. ∼45%\sim 45\% of blood volume): red blood cells (RBCs/erythrocytes), white blood cells (WBCs/leukocytes), and platelets (thrombocytes).
  • Plasma specifics
    • Blood Plasma ∼55%\sim 55\% of blood volume; Water: ∼90−92%\sim 90-92\% of plasma by volume (main solvent).
    • Proteins: ∼7−8%\sim 7-8\%; major ones: albumin ∼50−60%\sim 50-60\% of plasma protein, globulins ∼35−40%\sim 35-40\%, fibrinogen ∼4%\sim 4\%).
    • Normal total plasma protein: 6.0−8.0 g/dL6.0-8.0\,\text{g/dL}.
    • Electrolytes: Na+, K+, Cl−, HCO3−, Ca2+, Mg2+ — concentrations similar to basic metabolic panels.
    • Other solutes: glucose, amino acids, lipids, urea, creatinine, gases (dissolved O2, CO2), hormones, vitamins, and waste products.
    • Serum vs plasma: serum = plasma minus clotting factors.
  • Formed elements
    • Red blood cells (RBCs/erythrocytes):
    • Function: transport O2 via hemoglobin (Hb) and CO2; help regulate pH.
    • Lifespan: ∼120 days\sim 120\text{ days}.
    • Typical lab values (adults):
      • Hgb (hemoglobin): Men ∼13.5−17.5 g/dL\sim 13.5-17.5\,\text{g/dL}, Women ∼12.0−15.5 g/dL\sim 12.0-15.5\,\text{g/dL}.
      • Hct (hematocrit): Men ∼41−53%\sim 41-53\%, Women ∼36−46%\sim 36-46\%.
      • RBC count: Men ∼4.5−6.0×106/μL\sim 4.5-6.0\times 10^{6}/\mu L, Women ∼4.0−5.5×106/μL\sim 4.0-5.5\times 10^{6}/\mu L.
    • White blood cells (WBCs/leukocytes):
    • Function: immune defense (infection, inflammation, allergy, malignancy).
    • Types and rough differential (percent of total WBC in healthy adults):
      • Neutrophils: 50−70%50-70\% — phagocytosis of bacteria; first-line innate response.
      • Lymphocytes: 20−40%20-40\% — B cells, T cells, NK cells; adaptive immunity.
      • Monocytes: 2−8%2-8\% — become tissue macrophages; phagocytosis, antigen presentation.
      • Eosinophils: 1−4%1-4\% — parasite defense, allergic responses.
      • Basophils: 0.5−1%0.5-1\% — release histamine/heparin in allergy.
    • Total WBC count: ∼4.0−11.0×103/μL\sim 4.0-11.0\times 10^{3}/\mu L.
    • Platelets (thrombocytes):
    • Function: primary hemostasis (aggregate and form platelet plug), support coagulation.
    • Normal count: ∼150−450×103/μL\sim 150-450\times 10^{3}/\mu L.
  • How composition is measured (common lab tests) (❹)
    • Complete blood count (CBC): RBC, Hgb, Hct, RBC indices (MCV, MCH, MCHC), WBC count and differential, platelet count.
    • Peripheral blood smear: morphology of RBCs, WBCs, platelets.
    • Basic/metabolic panels: electrolytes, glucose, renal function, etc.
    • Plasma protein tests: serum protein electrophoresis (SPEP) for globulin fractions; albumin by dye-binding.
    • Coagulation tests: PT/INR, aPTT, fibrinogen level.
  • Clinical significance — example scenarios (❺)
    • Anemia: low Hgb/Hct → fatigue, pallor; causes include blood loss, hemolysis, iron deficiency, chronic disease.
    • Leukocytosis (high WBC): often infection or inflammation; neutrophilia suggests bacterial infection, lymphocytosis suggests viral infection.
    • Thrombocytopenia (low platelets): bleeding risk; causes include immune destruction, marrow failure, drugs.
  • Additional notes (Page 4)
    • Hypoalbuminemia: edema, poor drug-binding, marker of liver disease or inflammation.
    • Hemoconcentration (dehydration): apparent high Hct and plasma protein; dilution (IV fluids) lowers Hct.