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Histology of Blood

Histology of Blood. BLOOD. Blood consists of fluid element (plasma) and formed elements cells: erythrocytes, platelets and leukocytes. Adult has about 5.5 Liters Blood is usually studied in stained smears using Leishmann or Giemsa stains.

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Histology of Blood

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  1. Histology of Blood

  2. BLOOD • Blood consists of fluid element (plasma) and formed elements cells: erythrocytes, platelets and leukocytes. • Adult has about 5.5 Liters • Blood is usually studied in stained smears using Leishmann or Giemsa stains. • Blood cells are produced in bone marrow from stem cells.

  3. Composition of Blood

  4. Erythrocytes (RBCS) • Shape: Biconcave disks which has no nucleus (large surface area for gas exchange). • Dimention: They are 7.2 - 7.4 µm in diameter and 2 µm in thickness in stained smears. • Rouleaux appearance in slow circulation.

  5. Flexible; squeeze when pass through capillaries. • Survive about 120 days in circulation. • Old RBC removed by macrophages in spleen and bone marrow. • Contains hemoglobin which is an endogenous pigment (greenish yellow) to carry oxygen.

  6. Adaptations of RBCS to function • Biconcavity: increase surface area/decrease distance for gas exchange. • Plasticity: passage through narrow capillaries • Rounded edges: no injury. • No organelles: space for hemoglobin. • Carbonic anhydrase: carry CO2.

  7. Numbers of RBCs • Normal: 4-6 million per mm³.

  8. Leucocytes • Number: 6-10,000 per mm³ • Granulocytes (polymorphonuclear leukocytes) have specific granule • neutrophils 60-70% • acidophils 2-4% • basophils 0.5-1% • Agranulocytes lack specific granule • lymphocytes 20-30% • monocytes 3-8% • Platelets 200,000-400,000 per mm³

  9. Eosinophil 2-4% Neutrophil 60-70% Basophil 0.5-1% Granular Leukocytes

  10. Lymphocyte 20-25% Monocyte 3-8% Agranular Leukocytes

  11. Neutrophils • 12-15 µm in diameter. • Multi-lobed nucleus. • Human females may have inactivated second X chromosome (drumstick). • Specific granules: Alkaline PO4ase, collagenase, lactoferrin, lysozyme and phagocytins. • Azurophilic granules: deep red or purple, primary lysosomes containing acid hydrolase myeloperoxidase, lysozyme.

  12. Neutrophils • Lifespan: 1-4 days in tissue. • Active phagocytes which are important in defense against infection. • Form H2O2 and powerful cytotoxins. • Lysozyme breaks down bacterial cell wall.

  13. Eosinophils • About 12-15 µm in diameter • Bi-lobed nucleus • Many granules (primary lysosomes) • Kill parasites, especially worms • Phagocytose Ag-Ab complexes to terminate allergic reactions.

  14. Basophils • Scarce, hard to find in smears • S-shaped nucleus • Ig E receptors on their plasmalemma • Many blue (basophilic) specific granules with heparin and histamine • Content of specific granules cause vasodilatation • Nonspecific granules are lysosomes • Function as initiator of the inflammatory process • May act as supplement of mast cell function

  15. Lymphocytes • 20-25 % of circulating leukocytes • 6-8 µm dia most common; large ones up to 18 µm dia also found in blood • Dark, heterochromatic nucleus • Thin layer of blue cytoplasm, many ribosomes • Three types: T-cells(80%), B-cells (15%) and Null cells(remainder) • Differentiation occurs in bone marrow (B cells) and thymus (T cells) • T-cells may live many years, B-cells live a few months

  16. Lymphocytes • B cells form plasma cells, function in humoral immunity via immunoglobulins • T cells function in cell-mediated immunity • Some T cells with “memory” of antigen exposure survive long periods; immunization • Null Cells are composed of: Stem cells and Natural killer cells • NK cells kill some foreign and virally alerted cells

  17. Monocytes • 12-20 µm in diameter • Oval, eccentric, horseshoe or kidney shaped nucleus • Lighter stained nucleus than large lymphocytes • Cytoplasm light blue due to azurophilic granules (lysosomes) and ribosomes • In tissues, differentiate into macrophages • Lifespan 12-100 hours • Do not re-enter into circulation

  18. Platelets • Non-nucleated disk-shaped cell fragments • 2-5 µm in diameter, derived from megakaryocyte cytoplasm • Life span less than 14 days in blood • Hyalomere is the peripheral clear region • Granulomere is the central darker region

  19. Platelet Function • Blood clotting; aggregation of platelets • Clot retraction due to actin/myosin • Clot removal due to plasmin which is a proteolytic enzyme

  20. THANK YOU

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