Monocyte (MAH-nuh-syt): The largest type of white blood cell (WBC) in peripheral blood; it has a large, kidney-shaped nucleus and abundant, pale cytoplasm. Its function is to circulate briefly before migrating into tissues to become a phagocytic macrophage.
Lymphocyte (LIM-fuh-syt): A small white blood cell with a large, spherical, dark-staining nucleus and very little pale cytoplasm; the main cell of the adaptive immune system, encompassing T cells and B cells.
Thrombocyte (Platelet) (THROM-boh-syt/PLATE-let): Small, anucleated, disc-shaped cellular fragments derived from megakaryocytes in the bone marrow; their primary function is to adhere to damaged vessel walls and initiate blood clotting (hemostasis).
Erythrocyte (Red Blood Cell) (uh-RITH-roh-syt): A biconcave, anucleated, disc-shaped cell filled with hemoglobin; its primary function is to transport oxygen from the lungs to the tissues.
Agranulocyte (ay-GRAN-yuh-loh-syt): A type of white blood cell characterized by the absence of prominent, specific granules in its cytoplasm when stained (e.g., lymphocytes and monocytes).
Non-specific granules (azurophilic granules) (non spuh-SIF-ik GRAN-yoolz): Lysosomes found in the cytoplasm of all white blood cells (agranulocytes and granulocytes); they stain dark purple/blue and contain enzymes for cellular digestion.
Erythropoiesis (uh-rith-roh-poy-EE-sis): The general process of red blood cell (erythrocyte) formation that occurs in the red bone marrow, involving cell division, hemoglobin synthesis, and the expulsion of the nucleus.
Proerythroblast (proh-uh-RITH-roh-blast): The earliest recognizable precursor cell in the erythropoiesis lineage; it is a large, highly mitotic cell with a large, pale nucleus and intensely basophilic cytoplasm (due to abundant ribosomes for hemoglobin synthesis).
Basophilic erythroblast (bay-suh-FIL-ik uh-RITH-roh-blast): The second stage in erythropoiesis; smaller than the proerythroblast, it is characterized by intense cytoplasmic basophilia (blue staining) as active hemoglobin synthesis begins.
Polychromatic erythroblast (pah-li-kroh-MAT-ik uh-RITH-roh-blast): The stage in erythropoiesis where the cell's cytoplasm begins to stain both blue (ribosomes) and pink (hemoglobin), giving it a muddy or grayish-purple color (polychromasia); cell division stops during this stage.
Condensed chromatin (heterochromatin) (kun-DENST KROH-muh-tin/HET-uh-roh-KROH-muh-tin): Chromatin that is tightly coiled and inactive; its progressive clumping and condensation is a key histological feature during the late stages of erythropoiesis as the nucleus prepares to be expelled.
Normoblast/orthochromatophilic erythroblast (NOR-moh-blast/OR-thoh-kroh-MAT-oh-FIL-ik uh-RITH-roh-blast): The final nucleated stage in erythropoiesis; the cytoplasm is predominantly pink (orthochromatophilic) due to the high concentration of hemoglobin, and the nucleus is small and very dense with condensed chromatin (pyknotic).
Reticulocyte (ruh-TIK-yuh-loh-syt): An immature red blood cell that has expelled its nucleus (ejects the pyknotic normoblast nucleus); it retains a small amount of residual ribosomal RNA (which stains blue/purple with special stains) and is released into the peripheral blood where it matures into a full erythrocyte within a day or two.
Monopoiesis (mah-nuh-poy-EE-sis): The process of monocyte formation from a myeloid stem cell in the bone marrow.
Myeloid progenitor cell (MY-uh-loyd proh-JEN-uh-ter sell): A multipotent stem cell in the bone marrow that gives rise to most of the blood cell types, including erythrocytes, thrombocytes, monocytes, and granulocytes.
T cell (tee sell): A lymphocyte that mediates cell-mediated immunity; it matures in the thymus and is responsible for recognizing and destroying abnormal cells.
B cell (bee sell): A lymphocyte that mediates humoral immunity; it matures in the bone marrow and, upon activation, differentiates into plasma cells that secrete antibodies.
Thrombopoiesis (throm-boh-poy-EE-sis): The process of thrombocyte (platelet) formation, involving the fragmentation of the cytoplasm of a large cell called a megakaryocyte in the bone marrow.
Lymphopoiesis (lim-fuh-poy-EE-sis): The process of lymphocyte formation, primarily occurring in the bone marrow and peripheral lymphoid organs (like lymph nodes and the thymus).
Granulocytes (GRAN-yuh-loh-syts): A class of white blood cells (including neutrophils, eosinophils, and basophils) characterized by the presence of prominent specific cytoplasmic granules that stain differentially and mediate the cell's unique function.
Neutrophil (NOO-truh-fil): The most abundant type of granulocyte and white blood cell; its nucleus is multilobed (3-5 lobes), and its specific granules stain faintly (neutral pink/lilac). Its primary function is to phagocytize and destroy bacteria.
Neutrophil drumstick (NOO-truh-fil DRUM-stik): A small, highly condensed, bulbous projection of the nucleus seen in about 3% of neutrophils in females; it represents the inactive X chromosome (Barr body) and is a sex chromatin identifier.
Basophil (BAY-suh-fil): The least common type of granulocyte; it is characterized by large, dark blue/purple specific granules that often obscure the bilobed nucleus. It releases mediators (like histamine) central to inflammatory and allergic reactions.
Eosinophil (ee-oh-SIN-uh-fil): A granulocyte characterized by a bilobed nucleus and large, refractive, red/pink-staining specific granules (acidophilic); its function is to combat parasites and modulate allergic and chronic inflammatory reactions.
Granulopoiesis (gran-yuh-loh-poy-EE-sis): The general process of granulocyte formation (leading to neutrophils, eosinophils, and basophils) from the myeloid progenitor cell in the bone marrow.
Promyelocyte (proh-MY-uh-loh-syt): An early, large, highly mitotic precursor cell in the granulopoiesis lineage; it is the first stage where large, dark-staining non-specific granules (azurophilic granules) appear in the cytoplasm.