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Blood – Part 2

Blood – Part 2. Classification of WBCs. WBCs are classified into two major groups, depending on whether or not they contain visible granules in their cytoplasm. Granulocytes – Granule containing WBCs. Agranulocytes – Lack visible cytoplasmic granules. Granulocytes.

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Blood – Part 2

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  1. Blood – Part 2

  2. Classification of WBCs • WBCs are classified into two major groups, depending on whether or not they contain visible granules in their cytoplasm. • Granulocytes – Granule containing WBCs. • Agranulocytes – Lack visible cytoplasmic granules.

  3. Granulocytes • Granulocytes – Granule containing WBCs. • Have lobed nuclei • Typically consist of several rounded nuclear areas connected by thin strands of nuclear material. • The granules in their cytoplasm stain specifically with Wright’s stain. • Granulocytes include the: • Neutrophils • Eosinophils • Basophils

  4. Neutrophils • Multilobed nucleus. • Very fine granules that respond to both acid and basic stains. • The cytoplasm as a whole stains pink. • Avid phagocytes at sites of acute infection.

  5. Eosinophils • Blue-red nucleus. • Resembles an old fashioned telephone receiver. • Large brick-red cytoplasmic granules. • Their number increases rapidly during allergies and infections by parasitic worms (ex: tapeworms and flatworms)

  6. Basophils • Rarest of the WBCs. • Contain large histamine- containing granules that stain dark blue. • Histamine – Inflammatory chemical that makes blood vessels leaky and attracts other WBCs to the inflammatory site.

  7. Agranulocytes • Agranulocytes – lack visible cytoplasmic granules. • Their nuclei is closer to the norm – that is spherical, oval, or kidney shaped. • The agranulocytes include: • Lymphocytes • Monocytes

  8. Lymphocytes • Have a large, dark purple nucleus that occupies most of the cell volume. • Slightly larger than RBCs. • Tend to take up residence in lymphatic tissues, where they play an important role in the immune response.

  9. Monocytes • Largest of the WBCs. • Except for their more abundant cytoplasm and indented nucleus, they resemble large lymphocytes. • When they migrate into the tissues, they change into macrophages with huge appetites. • Macrophages are very important in fighting chronic infections.

  10. Platelets • Platelets – One of the irregular cell frag- ments of blood. • Not cells in the strict sense; They are fragments of bizarre multinucleate cells called megakaryocytes. • Megakaryocytes rupture releasing thousands of anucleate “pieces” that quickly seal themselves off from the surrounding fluids.

  11. Platelets • Appear as darkly staining, irregularly shaped bodies scattered among the other blood cells. • Needed for the clotting process.

  12. Hematopoiesis • Hematopoiesis – Blood cell formation. • Occurs in red bone marrow. • This tissue is found chiefly in the: • Flat bones of the skull and pelvis • Ribs • Sternum • Proximal epiphyses of the humerus and femur • After the cells mature, they are discharged into the blood vessels surrounding the area.

  13. Hemocytoblast • All the formed elements arise from a common type of stem cell, the hemocytoblast. • Hemocytoblasts resides in the bone marrow. • Their development differs and once a cell is committed to a specific blood pathway it cannot change.

  14. The Aging of RBCs • Because they are anucleate, RBCs are unable to synthesize proteins, grow, or divide. • As they age, RBCs become more rigid and begin to fragment, or fall apart in 100-120 days. • Their remains are eliminated by phagocytes in the liver, spleen, and other body tissues. • Lost cells are replaced by the division of hemocytoblasts.

  15. Developing RBCs • The developing RBCs divide many times and then begin synthesizing huge amounts of Hb. • When enough Hb has been accum- ulated, the nucleus and most organelles are ejected and the cell collapses inward. • The entire develop- mental process from hemocytoblast to mature RBC takes 3-5 days.

  16. Erythropoietin • The rate of erythrocyte production is controlled by a hormone called erythropoietin. • Normally a small amount of erythropoietin circulates in the blood at all times, and RBC are formed at a fairly constant rate. • The kidneys play the major role in producing this hormone. • If blood levels of O2 begin to decline, the kidneys step up their release of erythropoietin. • An excessive amount of O2 in the bloodstream, depresses erythropoietin release.

  17. Formation of Leukocytes and Platelets • The formation of leukocytes is stimulated by two hormones: • Colony Stimulating Factors (CSFs) • Interleukins • The production of platelets is accele- rated by the hormone thrombopoietin.

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