Hem 07

Leukocytes (leucocytes) (white blood cells) (WBCs) • •

Largest blood cells Colorless,

•

Lack hemoglobin, With nuclei and organelles and some have granules Defense mechanism against disease. Diapedesis

% It is the capacity of recognition of specific sites in the walls of blood vessels and squeezing through these locations using an amoeboid motion. ^ There are about 5,000–11,000 white blood cells /mm3 of blood.

Leukocytes (continue) There are two varieties  I- Granulocytes: Have inclusions in their cytoplasm With lobulated or segmented nuclei. 35–85 They are formed in the bone marrow . Account for about 70% of all white blood cells. Water diffuses into the cell till equilibrium is established. They include three types of cells which are neutrophils, eosinophils and basophils.

Leukocytes (continue) 1- Neutrophils (polymorphonuclear leukocytes) (heterophils): Constitute 65–75% of leukocyte count. It is 10-14 μ in diameter. Granules which stain with neutral dyes and eosin may appear to be pink to purple. These granules are lysosomes with which they destroy bacteria. They travel about by amoeboid movement and can surround and destroy bacteria and other foreign particles.

Leukocytes (continue): Neutrophils Its nucleus forms one or two lobes, but as the cell matures it develops more and more. have 3 to 5 lobes, connected together with fine threads of chromatin hence the name of polymorphonuclear leukocyte was applied. Neutrophils are phagocytes, particularly for bacteria. They engulf and destroy invading bacteria and then die. Their dead and lysed bodies constitute the bulk of pus

- Eosinophils (acidophils):.

0-12 μ

onstituting about 1% of the leukocyte count

umber increases in the presence of allergic disorders and parasitic infestations.

Leukocytes (continue ): Eosinophil

The nucleus is bi-lobed which are joined by a thin thread of chromatin. The granules which fill the cytoplasm are larger than those of the neutrophils and stain with acid dyes such as eosin with a pinkish red color. Like the granules of neutrophils, the eosinophil's granules contain lytic enzymes, but they're much larger than those of neutrophils.

Eosinophils, which are particularly active against parasitic infections, exert their action by discharging highly active elements from preformed granules It's known that the eosinophil counters the action of many mast cell mediators by secreting degradative enzymes, including histaminase and aryl sulphatase, which destroy histamine and leukotrienes, respectively.

Leukocytes (continue): Eosinophil In helminthic infestation, major basic protein and eosinophil cationic protein released from the eosinophil are probably beneficial in promoting elimination of the parasites. Eosinophils chemotactically aggregate in large numbers to sites where antigen-antibody complexes are found and where the host is attempting to deal with foreign bodies.

Leukocytes (continue): Eosinophil 3- Basophils: The rarest of all of the formed elements They are absent in cats, rats and mice. The basophils account for about 1% of the granulocytes. The nucleus may appear elongated or with one or more constrictions. The granules are moderately large, stain with basic dyes with a deep purple color and are water-soluble. They release chemicals such as histamine and play a role in the inflammatory response to infection. Basophils contain granules having the same materials as mast cells.

II- Agranulocytes: Have not inclusions in their cytoplasm Do not have lobulated or segmented nuclei. They include lymphocytes and monocytes. 1- Lymphocytes: The most numerous and most important Make up about 20% - 35% of all leukocyte count. The nucleus occupies nearly the whole volume of the cell The cytoplasm which surrounds it forms a thin shell Very high ratio of nucleus to cytoplasm.

II- Agranulocytes (continue): They may divide into small, medium and large lymphocytes: The small lymphocytes are spherical, of about 5-10 μ and constitute most of lymphocyte count. The medium (10-18 μ) and large lymphocytes are relatively scarce. The large size is usually found outside the circulation, mostly in lymphatic organs. There are two functional types of lymphocytes which are B lymphocytes (B cells) T lymphocytes (T cells) They are morphologically indistinguishable.

II- Agranulocytes (continue): 2- Monocytes: The largest of the circulating formed elements (18-25 μ). They constitute 3–8% of the white blood cells. The nucleus is relatively small and varies in form (may be kidney shaped, bean shaped or horseshoe shaped). The cytoplasm is relatively larger in volume than that in lymphocytes Monocytes are derived from the phagocytic cells that line many vascular and lymph channels, called the reticuloendothelial system. They move to areas of infection, where they are transformed into macrophages, (large phagocytic cells) that trap and destroy microorganisms left behind by the granulocytes and lymphocytes.

II- Monocytes (continue): Monocytes are derived from the phagocytic cells that line many vascular and lymph channels, called the reticuloendothelial system. They move to areas of infection, where they are transformed into macrophages, (large phagocytic cells) that trap and destroy microorganisms left behind by the granulocytes and lymphocytes. In certain diseases of long duration (tuberculosis, malaria and typhoid) the monocytes act as the main instrument of defense.

Leukocytes On the other hand, WBCs are subdivided on the basis of their functions into: * Phagocytic (eater) cells which include neutrophils, monocytes and eosinophils * Non-phagocytic cells which include lymphocytes and basophils.

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