When aging RBCs develop subtle changes, macropha—ges in the bone marrow, spleen, and liver engulf and digest them. The iron is carried by transferring in the blood to certain tissues, where it combines with apoferritin to form ferritin. The heme is catabolized into biliver—din, which is converted to bilirubin. The latter is secreted with bile salts.
Platelets (thromboplastids) are 2–3 mm in diameter.
They are a nuclear, membrane—bound cellular fragments derived by cytoplasmic fragmentation of giant cells, called megakaryocytes, in the bone marrow.
They have a short life span of approximately 10 days.
There are normally 150 000–400 000 platelets per mm3 of blood. Ultrastructurally, platelets contain two portions: a peripheral, light—staining hyalomere that sends out fine cytoplasmic processes, and a central, dark—staining granulomere that con tains mitochondria, vacuoles, glycogen granules, and granules. Platelets seal minute breaks in blood vessels and maintain endothelial integrity by adhering to the damaged vessel in a process known as platelet aggregation. Platelets are able to form a plug at the rupture site of a vessel because their mem brane permits them to agglutinate and adhere to surfaces.
Platelets aggregate to set up the cascade of enzymatic reac tions that convert fibrinogen into the fibrin fibers that make up the clot.
New words
mesodermal – мезодермальный
erythrocytes – эритроциты
platelets – тромбоциты
carbon – углерод
dioxid – диоксид
span – промежуток
light—staining – легкое окрашивание
to aggregate – соединяться
19. Blood. Formed elements of the blood. Leukocytes
Leukocytes, or white blood cells, are primarily with the cellular and humoral defense of the organism foreign materials. Leukocytes are classified as granulocytes (neutrophils, eos—inophils, basophils) and agranulocytes (lympmonocytes).
Granulocytes are named according to the staining properties of their specific granules. Neutrophils sare 10–16 mm in diameter.
They have 3–5 nuclear lobes and contain azurophilic granules (lysosomes), which contain hydrolytic enzymes for bacterial destruction, in their cytoplasm. Neutrophils are phagocytes that are drawn (chemotaxis) to bacterial che—moattractants. They are the primary cells involved in the acute inflammatory response and represent 54–62 % of leukocytes.
Eosinophils: they have a bilobed nucleus and possess acid granulations in their cytoplasm. These granules contain hydrolytic enzymes and peroxidase, which a discharged into phagocytic vacuoles.
Eosinophils are more numerous in the blood during allergic diseases; they norma asent only – 3 % of leukocytes.