Histology of Blood (Part 2) PDF

JABIR IBN HAYYAN MEDICAL Lecture By : Alaa AL Hussainy UNIVERSITY COLLEGE OF MEDICINE Lec :5 DEPARTMENT OF HUMAN ANATOMY Section of Histology...

JABIR IBN HAYYAN MEDICAL Lecture By : Alaa AL Hussainy UNIVERSITY COLLEGE OF MEDICINE Lec :5 DEPARTMENT OF HUMAN ANATOMY Section of Histology HISTOLOGY OF BLOOD (part 2) Leukocytes The number of leukocytes in the blood varies according to age, sex, and physiologic conditions, Healthy adults have 4500 to 11,000 leukocytes per microliter of blood. Leukocytes (white blood cells or WBCs) leave the blood and migrate to the tissues where they become functional and perform various activities related to immunity. According to the type of cytoplasmic granules and their nuclear morphology, leukocytes are divided into two groups: 1-Granulocytes 2-Agranulocytes. Both types are rather spherical while suspended in blood plasma, but they become amoeboid and motile after leaving the blood vessels and invading the tissues. Their estimated sizes mentioned here refer to observations in blood smears in which the cells are spread and appear slightly larger than they are in the circulation. 1 A) Granulocytes Possess two major types of cytoplasmic granules: 1)Lysosomes(often called azurophilic granules in blood cells). 2)Specific granules that bind neutral, basic, or acidic stains and have specific functions. Granulocytes have polymorphic nuclei with two or more distinct (almost separated) nuclear lobes, granulocytes include the following: 1-Neutrophils. 2-Eosinophils. 3-Basophils. All granulocytes are terminally differentiated cells with a life span of only a few days. Their Golgi complexes and rough ER are poorly developed. They have few mitochondria and depend largely on glycolysis for their low energy needs. Granulocytes normally die by apoptosis in the connective tissue and billions of neutrophils alone die by apoptosis each day in the adult human. The resulting cellular debris is removed by macrophages and, like all apoptotic cell death, does not itself elicit an inflammatory response. B ) Agranulocytes Do not have specific granules, but they do contain azurophilic granules (lysosomes), with affinity for the basic stain azure A. The nucleus is spherical or indented but not lobulated. This group includes: 1-Lymphocytes. 2- Monocytes. The differential count (is the percentage of all leukocytes for each type of leukocyte). 2 All leukocytes are key players in the defense against invading microorganisms, and in the repair of injured tissues, specifically leaving the microvasculature in injured or infected tissues. A) Granulocytes 1)Neutrophils (Polymorphonuclear Leukocytes) Mature neutrophils constitute 54% to 62% of circulating leukocytes , neutrophils are 12-15 μm in diameter in blood smears, with nuclei having two to five lobes linked by thin nuclear extensions. In females, the inactive X chromosome may appear as a drumstick -like appendage on one of the lobes of the nucleus although this characteristic is not obvious in every neutrophil. Neutrophils are inactive and spherical while circulating but become actively amoeboid during diapedesis and upon adhering to solid substrates such as collagen in the ECM. Neutrophils are active phagocytes of bacteria and other small particles and are usually the first leukocytes to arrive at sites of infection, where they actively pursue bacterial cells using chemotaxis. The cytoplasmic granules of neutrophils provide the cells’functional activities and are of two main types. 1)Azurophilic primary granules. 2)Specific secondary granules. In a process called diapedesis (Gr. dia, through + pedesis, to leap), the leukocytes send extensions through the openings between the endothelial cells, migrate out of the venules into the surrounding tissue space, and head directly for the site of injury or invasion. The attraction 3 of neutrophils to bacteria involves chemical mediators in a process of chemotaxis, which causes leukocytes to rapidly accumulate where their defensive actions are specifically needed. Neutrophils are short-lived cells with a half-life of 6 to 8 hours in blood and a life span of 1 to 4 days in connective tissues before dying by apoptosis. 2- Eosinophils Eosinophils are far less numerous than neutrophils, constituting only 1% to 3% of leukocytes. In blood smears, this cell is about the same size as a neutrophil or slightly larger, but with a characteristic bilobed nucleus. The main identifying characteristic is the abundance of large, acidophilic specific granules typically staining pink or red. 4 Eosinophils act to kill parasitic worms or helminthes, modulate inflammatory responses, have important role in the inflammatory response triggered by allergies and particularly abundant in connective tissue of the intestinal lining and at sites of chronic inflammation, such as lung tissues of asthma patients. These leukocytes also remove antigen-antibody complexes from interstitial fluid by phagocytosis. 3) Basophils Basophils are also 12 to 15 μm in diameter but make up less than 1% of blood leukocytes and are therefore difficult to find in normal blood smears. The nucleus is divided into two irregular lobes, but the large specific granules overlying the nucleus usually obscure its shape. The specific granules (0.5 μm in diameter) typically stain purple with the basic dye of blood smear stains and are fewer, larger, and more irregularly shaped than the granules of other granulocytes. The strong basophilia of the granules is due to the presence of heparin and other sulfated GAGs. Basophilic specific granules also contain much histamine and various other mediators of inflammation. B ) Agranulocytes 1) Lymphocytes By far the most numerous type of agranulocyte in normal blood smears or CBCs, lymphocytes constitute a family of leukocytes with spherical nuclei. Lymphocytes are typically the smallest leukocytes and are abundant, constituting up to a third of these cells. 5 Although they are morphologically similar, lymphocytes can be subdivided into functional groups by distinctive surface molecules (called “cluster of differentiation” or CD markers) that can be distinguished using antibodies with immunocytochemistry or flow cytometry. Major classes Include: 1-B lymphocytes. 2-T lymphocytes {Helper and Cytotoxic (CD4+ and CD8+, respectively)}. 3-Natural Killer (NK)cells. These and other types of lymphocytes have diverse roles in immune defenses against invading microorganisms and certain parasites or abnormal cells. Though generally small circulating lymphocytes have a wider range of sizes than most leukocytes. Many have diameters similar to those of RBCs; medium and large lymphocytes are 9 to 18 μm in diameter, with the latter representing activated lymphocytes or NK cells. The small lymphocytes are characterized by spherical nuclei with highly condensed chromatin and only a thin surrounding rim of scant cytoplasm,making them easily distinguishable from granulocytes. Larger lymphocytes have larger, slightly indented nuclei and more cytoplasm that is slightly basophilic, with a few azurophilic granules (lysosomes), mitochondria, free polysomes, and other organelles. Lymphocytes vary in life span according to their specific functions; some live only a few days and others survive in the circulating blood or other tissues for many years. 6 2) Monocytes Monocytes are agranulocytes that are precursor cells of macrophages, osteoclasts, microglia, and other cells of the mononuclear phagocyte system in connective tissue. All monocyte- derived cells are antigen-presenting cells and have important roles in immune defense of tissues. Circulating monocytes have diameters of 12 to 15 μm, but macrophages are somewhat larger. The monocyte nucleus is large and usually distinctly indented or C-shaped. The chromatin is less condensed than in lymphocytes and typically stains lighter than that of large lymphocytes. The cytoplasm of the monocyte is basophilic and contains many small lysosomes or azurophilic granules, some of which are at the limit of the light microscope’s resolution. These granules are distributed through the cytoplasm, giving it a bluish-gray color in stained smears. Platelets Blood platelets (or thrombocytes) are very small non-nucleated, membrane- bound cell fragments only 2 to 4 μm in diameter. Platelets originate by separation from the ends of cytoplasmic processes extending from giant polyploid bone marrow cells called megakaryocytes. Platelets promote blood clotting and help repair minor tears or leaks in the walls of small blood vessels, preventing loss of blood from the microvasculature. Normal platelet counts range from 150,000 to 400,000/μL (mm3) of blood. Circulating platelets have a life span of about 10 days. 7 In stained blood smears, platelets often appear in clumps. Each individual platelet is generally discoid, with a very lightly stained peripheral zone, the hyalomere, and a darker-staining central zone containing granules, called the granulomere. A sparse glycocalyx surrounding the platelet plasma lemma is involved in adhesion and activation during blood coagulation. ---------------------------------------------------------------------------------------------------------------- ❯❯ MEDICAL APPLICATION lymphocytes are obviously important in many diseases. Lymphomas are a group of disorders involving neoplastic proliferation of lymphocytes or the failure of these cells to undergo apoptosis. Although often slow-growing, all lymphomas are considered malignant because they can very easily become widely spread throughout the body. ------------------------------------------------------------------------------------------------------------- ❯❯ MEDICAL APPLICATION Aspirin and other nonsteroidal anti-inflammatory agents have an inhibitory effect on platelet function and blood coagulation because they block the local prostaglandin synthesis that is needed for platelet aggregation, contraction, and exocytosis at sites of injury. 8