Osteogenesis imperfectaA large and miscellaneous group of conditions of abnormal fragility and plasticity of bone, with recurring fractures on trivial trauma.
OsteoprogenitorA cell-type that differentiates into a mature osteocyte.
Ovarian follicleAn external, fluid-filled portion of the ovary in which oocytes mature before ovulation.
OviductThe passage through which the ova travel from the ovary into the uterus.
pancreasA glandular organ located in the abdomen. It makes pancreatic juices, which contain enzymes that aid in digestion, and it produces several hormones…
Pancreatic beta cellsCells of the pancreas (located in pancreatic islets, or islets of Langerhans) that produce insulin.
Paracrine factorsCytokines or hormones that act on cells or tissues within an extremely limited area.
Parkinson disease(PAR-kin-sun dih-ZEEZ) A progressive disorder of the nervous system marked by muscle tremors, muscle rigidity, decreased mobility, stooped posture, slow…
ParthenogenesisProduction of an embryo from an unfertilized egg.
PassageThe transfer or transplantation of cells from one culture medium to another.
PhenotypeThe observable characteristics of an organism, the expression of gene alleles (genotype) as an observable physical or biochemical trait. See Genotype.
Phenotypic characteristicsThe genetically and environmentally determined physical characteristics of an organism.
PlacentaThe organ that nourishes the developing fetus in the uterus.
PlasticityA phenomenon used to describe a cell that is capable of becoming a specialized cell type of different tissue.
PlateletsSmall, irregularly-shaped bodies in the blood that contain granules. These cells are important components of the blood coagulation (clotting) system.
Pluripotent(ploo-RIH-poh-tent) Able to mature or develop in any of several ways.
Pluripotent stem cell (PSC)A single stem cell that has the capability of developing cells of all germ layers (endoderm, ectoderm, and mesoderm).
Pluripotent stem cellsStem cells that can become all the cell types that are found in an implanted embryo, fetus, or developed organism, but not embryonic components of the…
Polar BodyA polar body is a structure produced when an early egg cell, or oogonium, undergoes meiosis.
PolarityThe observed differentiation of an organism, tissue or cell into parts having opposed or contrasted properties or form.
Population doublingsThe number of times cells growing in vitro have increased the total number of cells by a factor of 2 compared to the initial number of cells.
Post-implantation embryoImplanted embryos in the early stages of development until the establishment of the body plan of a developed organism with identifiable tissues and organs.
Pre-implantation embryoThe very early, free-floating Embryo, from the time the egg is fertilized until implantation in the mother's womb is complete.
Pre-implantation embryosFertilized eggs (zygotes) and all of the developmental stages up to, but not beyond, the blastocyst stage.
Precursor CellsIn fetal or adult tissues, these are partly differentiated cells that divide and give rise to differentiated cells. Also known as progenitor cells.
PreimplantationWith regard to an embryo, preimplantation means that the embryo has not yet implanted in the wall of the uterus.
Primitive streakThe initial band of cells from which the embryo begins to develop. The primitive streak establishes and reveals the embryo's head-tail and left-right…
Primordial germ cellA gamete, that is, a sperm or egg, OR a primordial cell that can mature into a sperm or egg.
Progenitor cellA progenitor cell, often confused with stem cell, is an early descendant of a stem cell that can only differentiate, but it cannot renew itself anymore.
ProliferationIncrease by frequent and repeated reproduction; growth by cell division.
Radiation Oncologist(RAY-dee-AY-shun on-KAH-loh-jist) A doctor who specializes in using radiation to treat cancer.
Radioimmunoassay(Abbreviation: RIA). An assay based on the use of a radioactively labelled antibody, where the amount of radiation detected indicates the amount of target…
Red Blood CellsCells that carry oxygen throughout the body (also called erythrocytes).
Regenerative medicineMedical interventions that aim to repair damaged organs, most often by using stem cells to replace cells and tissues damaged by aging and by disease.
Reproductive cloningSomatic cell nuclear transfer used for the production of a fetus and delivery of a live offspring that is genetically identical the donor of the somatic…
Retinoic acid(REH-tih-NOH-ik A-sid) A form of vitamin A that is made by the body, and can also be made in the laboratory.
Ribonucleic acid (RNA)A chemical similar to a single strand of DNA. In RNA, the letter U, which stands for uracil, is substituted for T in the genetic code.
RibosomeCellular organelle that is the site of protein synthesis during translation. See Organelle, Translation.
Salivary gland(SA-lih-VAYR-ee gland) A gland in the mouth that produces saliva.
Schwann cellA type of glial cell of the peripheral nervous system that helps separate and insulate nerve cells.
Side population (SP) stem cellTwo examples of multipotent stem cell populations found in bone marrow and skeletal muscle. SPs are not yet fully characterized.
SignalsInternal and external factors that control changes in cell structure and function.
Single-cell clonedA procedure pertaining to cells in vitro in which the descendants of a single cell are physically isolated from other cells growing in a dish, and then…
Skin biopsyProcess of removing tissue, in this case skin, from living patients for diagnostic examination, or the tissue specimen obtained by that process.
Somatic cell(soh-MA-tik ...) Any of the body cells except the reproductive (germ) cells.
Somatic cell nuclear transferA technique in which the nucleus of a somatic cell (any cell of the body except sperm cells and egg cells) is injected, or transfered, into an egg, that…
Somatic Cell Nuclear Transfer (SCNT)A method of cloning: transfer of the nucleus from a donor somatic cell into an enucleated egg to produce a cloned embryo.
Somatic cellsCells of body tissues other than the germline.
Somatic stem cellsNon-embryonic stem cells that are not derived from gametes (egg or sperm cells).
Stem cellA cell from which other types of cells develop. For example, blood cells develop from blood-forming stem cells.
Stem cell antigen 1 (Sca-1)Cell-surface protein on bone marrow cell, indicative of hematopoietic stem cells and mesenchymal stem cells.
Stem cell factor (SCF)Relatively undifferentiated cell that can continue dividing indefinitely, throwing off daughter cells that can undergo terminal differentiation into…
Stem cellscells that have the ability to divide for indefinite periods in culture and give rise to specialized cells.
StromalRelating to the stroma of an organ or other structure, that is, its framework, usually of connective tissue, rather than its specific substance.
Stromal cell(STROH-mul SEL) A type of cell that makes up certain types of connective tissue (supporting tissue that surrounds other tissues and organs).
Stromal cellsNon-blood cells derived from blood organs, such as bone marrow or fetal liver, which are capable of supporting growth of blood cells in vitro.
SubculturingTransferring cultured cells, with or without dilution, from one culture vessel to another.
Sulfated proteoglycanMolecules found primarily in connective tissues and joint fluids and that provide lubrication.
Surface markerSurface proteins that are unique to certain cell types capable of detection by antibodies or other detection methods.
Surface markersProteins on the outside surface of a cell that are unique to certain cell types, which are visualized using antibodies or other detection methods.
SyncytiotrophoblastA multinucleated cell formed from the cells of the trophoblast. Only a small area of the syncytiotrophoblast is evident at the start of the formation of…
syncytiumA large cell-like structure formed by the joining together of two or more cells. The plural is syncytia.
T cellOne type of white blood cell that attacks virus-infected cells, foreign cells, and cancer cells.
T cellsA type of white blood cell that is of crucial importance to the immune system. Immature T cells migrate to the thymus gland in the upper chest cavity…
T lymphocyteOne type of white blood cell that attacks virus-infected cells, foreign cells, and cancer cells.
TelomeraseAn enzyme that maintains the structure of the telomere by adding the required repetitive sequences to the ends of eukaryotic chromosomes.
Teratocarcinoma(TAYR-uh-toh-KAR-sih-NOH-muh) A type of germ cell cancer that usually forms in the testes (testicles).
TeratogenA drug or other agent that raises the incidence of congenital malformations.
Teratoma(tayr-uh-TOH-muh) A type of germ cell tumor that may contain several different types of tissue, such as hair, muscle, and bone.
Therapeutic cloningThe potential use of stem cells to grow, in vitro, tissue or organs for use in transplantation.
ThiazolidinedionesA class of antidiabetes drugs that enhances the activity of insulin.
Thrombocyte (Platelet)A tiny, disc-shaped blood cell responsible for controlling abnormal or excessive bleeding.
Thrombopoietin(THROM-boh-POY-eh-tin) A substance made by the body that helps make blood cells, especially platelets.
ThymusAn organ that is part of the lymphatic system, in which T lymphocytes grow and multiply. The thymus is in the chest behind the breastbone.
Tissue cultureThe in vitro culture of cell s, tissue s or organ s in a nutrient medium under sterile conditions.
ToleranceA condition in which higher doses of a drug are required to produce the same effect achieved during initial use; often associated with physical dependence.
Tolerance inductionThe "education" process that T cells undergo to discriminate between self and foreign proteins. This process takes place primarily in the thymus.
TotipotentHaving to do with cells that are able to develop into any type of cell found in the body.
Totipotent stem cellsStem cells that can give rise to all cell types that are found in an embryo, fetus, or developed organism, including the embryonic components of the…
TransaminaseAn enzyme that catalyzes chemical reactions in the body in which an amino group is transferred from a donor molecule to a recipient molecule.
TranscriptionIn biology, the process by which a cell makes an RNA copy of a sequence of DNA that is a gene.
Transcription factorsSpecialized proteins that bind to specific sites on DNA and turn on or turn off the expression of different sets of genes.
TransdifferentiationThe ability of a particular cell of one tissue, organ or system, including stem or progenitor cells, to differentiate into a cell type characteristic of…
TranslationThe process of converting the genetic infor- mation of an mRNA on ribosomes into a polypeptide.
Transplantation(tranz-plan-TAY-shun) The replacement of tissue with tissue from the person's own body or from another person.
Transplantation biologyThe science that studies the transplantation of organs and cells. Transplantation biologists investigate scientific questions to understand why foreign…