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Related to helper cell: Effector T cells
A type of T lymphocyte whose surface is marked by CD4 receptors; it is involved in both cell-mediated and antibody-mediated immune responses. It secretes cytokines that stimulate the activity of B cells and other T cells and binds with class II histocompatibility antigens, which are processed by macrophages and other antigen-presenting cells. Synonym: helper T cell See: antigen processing; T cell; cell-mediated immunity
See also: cell
1. the basic structural unit of living organisms.
2. a small more or less enclosed space.
All living cells arise from other cells, either by division of one cell to make two, as in mitosis and meiosis, or by fusion of two cells to make one, as in the union of the sperm and ovum to make the zygote in sexual reproduction.
All cells are bounded by a structure called the cell membrane or plasma membrane, which is a lipid bilayer composed of two layers of phospholipids. Each layer is one molecule thick with the charged, hydrophilic end of the lipid molecules on the surface of the membrane and the uncharged hydrophobic fatty acid tails in the interior of the membrane.
Cells are divided into two classes, eukaryotic cells and prokaryotic cells:
Eukaryotic cells have a true nucleus, which contains the genetic material, composed of the chromosomes, each of which is a long linear deoxyribonucleic acid (DNA) molecule associated with protein. The nucleus is bounded by a nuclear membrane, which is composed of two lipid bilayer membranes.
Prokaryotic cells, the bacteria, have no nucleus, and their genetic material, consisting of a single circular naked DNA molecule, is not separated from the rest of the cell by a nuclear membrane.
Eukaryotic cells are larger and more complex than prokaryotic cells. They also have membrane-bounded structures, such as mitochondria, chloroplasts, Golgi apparatus, endoplasmic reticulum and lysosomes, that prokaryotic cells lack.
The contents of a cell are referred to collectively as the protoplasm. In eukaryotic cells the contents of the nucleus are referred to as nucleoplasm and the rest of the protoplasm as the cytoplasm.
The lipid bilayer of eukaryotic cells is impermeable to many substances, such as ions, sugars and amino acids; however, membrane proteins selectively move specific substances through the cell membrane by active or passive transport. Water, gases such as oxygen and carbon dioxide, and nonpolar compounds pass through the cell membrane by diffusion. Materials can also be engulfed and taken into the cell enclosed in a portion of the cell membrane. This is called phagocytosis when solids are ingested and pinocytosis when liquids are ingested. The reverse process is called exocytosis. All of these processes permit the cell to maintain an internal environment different from its exterior. See also body fluids.
The cells of the body differentiate during development into many specialized types with specific tasks to perform. Cells are organized into tissues and tissues into organs. Embedded in the cell membrane are a wide range of molecules that vary with the cell type and are typically composed of proteins or glycoproteins that have a cytoplasmic transmembrane and external domains. These molecules serve as cell receptors and are involved in signal transduction for a wide range of ligands, including hormones, cytokines and incidentally serve as receptors for viruses and drugs.
See also betz cells, gaucher's cells, golgi's cells, hela cells, hürthle cell, kupffer's cells, merkel cell, mesangial cell, neuroendocrine cell.
macrophages involved in the processing and presentation of antigens making them immunogenic.
acinar cell, acinous cell
any of the cells lining an acinus, especially applied to the zymogen-secreting cells of the pancreatic acini.
one that adheres to the glass or plastic container in cell cultures, to form the monolayer. See also cell culture.
1. cells in the islets of Langerhans that secrete glucagon.
2. acidophilic cells of the anterior pituitary.
see apud cells.
enterochromaffin cells containing cytoplasmic granules capable of reducing silver compounds, located throughout the gastrointestinal tract, chiefly in the basilar portions of the gastric glands and the crypts of Lieberkühn. They secrete serotonin.
an immature neutrophil in which the nucleus is not lobulated but is in the form of a continuous band, horseshoe shaped, twisted or coiled. Called also band-form granulocyte and stab cell.
an early keratinocyte, present in the basal layer of the epidermis.
cells in the cerebellar cortex whose axons carry basket-like groups of fibrils which enclose the cell body of each Purkinje cell.
1. basophilic cells in the pancreas that secrete insulin and make up most of the bulk of the islets of Langerhans; they contain granules that are soluble in alcohol.
2. basophilic cells of the anterior pituitary.
one of the formed elements of the blood. See also blood.
the nucleus of the cell and the adjacent cytoplasm in cells which have processes, e g. neurons which consist of a cell body, an axon and dendrites.
a nucleated cell in the lacunae of bone. Called also osteocyte.
cells whose cytoplasm shows fine brown granules when stained with potassium bichromate, occurring in the adrenal medulla and in scattered groups in various organs and throughout the body.
any of the cells derived from the fertilized ovum by mitosis; a blastomere.
see cell culture.
see cell cycle.
a cell formed by division of a mother cell.
fluid loss from cells due to elevation of the osmotic pressure of blood and tissue fluid; a potent stimulus to thirst.
macrophage-like cells with long, filamentous processes located in the cortex of lymph nodes and the skin. Important in antigen trapping, processing and presentation. See also langerhans' cell.
the process whereby cells become specialized usually with concurrent loss of reproductive capacity.
embryonic stem cell
a stem cell of fetal origin. See stem cell (below).
enlarged macrophages with enlarged lysosomes and much endoplasmic reticulum. May fuse to form multinucleated giant cell (below).
one of the groups of acidophilic cells in the adenohypophysis. Contains granules that stain with azocarmine dye.
a cell with a vacuolated appearance due to the presence of complex lipoids; seen in xanthoma.
see syncytial giant cell.
a large nerve cell, especially one of those of the spinal ganglia.
see germ cell.
a very large, multinucleate cell; applied to megakaryocytes of bone marrow, to giant cells formed by coalescence and fusion of macrophages occurring in infectious granulomas and about foreign bodies, and to certain cancer cells.
a unicellular mucous gland found in the epithelium of various mucous membranes, especially that of the respiratory passages and intestines.
one containing granules, such as a keratinocyte in the stratum granulosum of the epidermis, when it contains a dense collection of darkly staining granules.
see taste bud.
heart failure c's, heart lesion c's
iron-containing, rust-colored macrophages found in the pulmonary alveoli in congestive heart failure.
a subset of T lymphocytes which cooperate with B and other T lymphocytes for the synthesis of antibodies to many antigens; they play an integral role in immunoregulation.
immunologically competent cell
the cells of the connective tissue of the ovary or of the testis (Leydig's cells) which furnish the internal secretion of those structures, i.e. testosterone.
cells composing the islets of Langerhans in the pancreas. See alpha cells, beta cells (above).
specialized cells, containing secretory granules, located in the tunica media of the afferent glomerular arterioles. They cause aldosterone production by secreting the enzyme renin and play a role in the regulation of blood pressure and fluid balance.
K c's, killer c's
T lymphocytes or null lymphocytes that have cytotoxic activity against target cells coated with specific IgG antibody.
accumulation of cells between the arterioles at the glomerular hilus. Called also granular cell.
precursor of the malignant interdigitating reticular cell in Hodgkin-like lymphoma in humans.
interstitial cells of the testis, which secrete testosterone.
see cell culture.
the plump, pale-staining, polyhedral cells of the corpus luteum.
lymphocytes and plasma cells.
a connective tissue cell that has basophilic, metachromatic cytoplasmic granules that contain histamine, heparin, hyaluronic acid, slow-reacting substance of anaphylaxis (SRS-A), and, in some species, serotonin. Have Fc receptors specific for IgE in the cell membrane.
cell-mediated immune reaction
see cellular immunity.
movement of cells from their place of origin to other tissues; one of the fundamental processes of development.
see microglia. See also neuroglia cells (below).
milk cell count
see milk cell counts.
a cell that divides to form new, or daughter, cells.
a plasma cell with large, clear cytoplasmic pockets.
natural killer c's, NK c's
cells capable of mediating cytotoxic reactions without themselves being specifically sensitized against the target.
any cell of the nervous system; a neuron.
see isogenous groups.
neuroglia c's, neuroglial c's
lymphocyte-like cells that lack specific antigen receptors and other surface markers characteristic of B and T lymphocytes; they include K and NK cells; their numbers are elevated in active systemic lupus erythematosus and other disease states.
a set of specialized cells of the mucous membrane of the nose; the receptors for smell.
see c cell.
round, oval or polyhedral cells with foamy, lipid-containing cytoplasm found in the bone marrow and spleen in Niemann-Pick disease.
a spherical or ellipsoidal cell with a single, eccentrically placed nucleus containing dense masses of chromatin in a wheel-spoke arrangement, an area of perinuclear clearing which contains the Golgi apparatus, and generally abundant cytoplasm. Plasma cells are produced by cell division of B lymphocytes following antigen stimulation and are involved in the synthesis and release of antibody. Called also plasmacyte and plasmocyte.
a dividing keratinocyte of the prickle-cell layer of the epidermis, with delicate radiating process connecting with other similar cells.
large branching cells of the middle layer of the cerebellar cortex.
red cell, red blood cell
giant histiocytic cells, typically multinucleate, which are the common histological characteristic of Hodgkin's disease in humans.
the cells forming the reticular fibers of connective tissue; those forming the framework of lymph nodes, bone marrow and spleen. They are weakly phagocytic, stromal in origin and are distinct from the monocyte-macrophage system.
a cell of the reticuloendothelial system.
any of the large nucleated cells whose cell membrane spirally enwraps the axons of myelinated peripheral neurons supplying the myelin sheath between two nodes of Ranvier.
elongated cells in the tubules of the testes to which the spermatids become attached; they provide support, protection and, apparently, nutrition until the spermatids are transformed into mature spermatozoa.
a crescentic or sickle-shaped erythrocyte seen in some humans and deer. The abnormal shape caused by the presence of varying proportions of hemoglobin S.
a cell in which the nucleus has been pressed to one side by an accumulation of intracytoplasmic mucin.
the cells of the body other than the germ cells.
see fluorescence-activated cell sorter.
conversion of a simple cell type into a specialized cell type capable of a special function, e.g. a secretory cell; a major part of the growth of an embryo and the differentiation of basic mesenchymal tissue into specialized organs.
spindle shaped cells of the dermis or subcutis; principal component of spindle cell tumors.
spiculed mature erythrocyte.
flat, scalelike epithelial cells.
see band cell (above).
any star-shaped cell, as a Kupffer cell or astrocyte, having many filaments extending in all directions.
1. any precursor cell.
2. a primitive hematopoietic cell that is capable of self-replicating or differentiating into precursor cells of erythrocytes or any of the leukocytes.
an erythrocyte containing granules that take a basic or bluish stain with Wright's stain.
a not well defined subset of T lymphocytes that are reported to inhibit antibody and cell-mediated immune responses. They may play a role in immunoregulation, and are believed to be abnormal in various autoimmune and other immunological disease states. See also T lymphocytes.
1. an abnormally thin erythrocyte showing, when stained, a dark center and a peripheral ring of hemoglobin, separated by a pale, unstained zone containing less hemoglobin; seen in various anemias and other disorders. Called also codocyte.
2. any cell selectively affected by a particular agent, such as a hormone or drug.
3. cell containing nonself antigens in its cell membranes that is a target for nonimmune and immune cytolysis, e.g. virus-infected or tumor cell.
cells in the taste buds associated with the nerves of taste.
see glandular therapy.
an embryonic cell that is capable of developing into any type of body cell.
a lymphocyte with increased basophilia.
the neuroepithelial elements of the retina.
white cell, white blood cell