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Glossary Blastocyst — A preimplantation embryo of about 150 cells produced by cell division following fertilization. The blastocyst is a sphere made up of an outer layer of cells (the trophoblast), a fluid-filled cavity (the blastocoel), and a cluster of cells on the interior (the inner cell mass). Cell-based therapies — Treatment in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cells or tissues. Cell culture — Growth of cells in vitro in an artificial medium for experimental research. Clone — Generate identical copies of a molecule, cell, or organism.When it is used to refer to cells grown in a tissue culture dish, a clone is a line of cells that is genetically identical to the originating cell. This is referred to as therapeutic cloning. The term clone may also be used to refer to an animal produced by nuclear transfer and then transplanted into a uterus. This is reproductive cloning. Cord blood stem cells — See Umbilical cord blood stem cells. Culture medium — The liquid that covers cells in a culture dish and contains nutrients to feed the cells. Medium may also include other growth factors added to produce desired changes in the cells. Embryo — In humans, the developing organism from the time of fertilization until the end of the eighth week of gestation, when it is called a fetus. Embryonic stem cells — Primitive (undifferentiated) cells derived from a 5-day preimplantation embryo that have the potential to become every cell type in the body. Embryonic stem cell line — Embryonic stem cells, which have been cultured under in vitro conditions that allow proliferation without differentiation for months to years. Fertilization — The joining of the male gamete (sperm) and the female gamete (egg). Fetus — A developing human from approximately eight weeks after conception until the time of its birth. Gamete — An egg (in the female) or sperm (in the male) cell. See also Somatic cell. Gene — A functional unit of heredity that is a segment of DNA found on chromosomes in the nucleus of a cell. Genes direct the formation of an enzyme or other protein. Human embryonic stem cell (hESC) — A type of pluripotent stem cell derived from the inner cell mass (ICM) of the blastocyst that can form every cell type in the body. In vitro — Latin for "in glass"; in a laboratory dish or test tube; an artificial environment. In vitro fertilization — A technique that unites the egg and sperm in a fertility clinic, instead of inside the female body. Inner cell mass (ICM) — The cluster of cells inside the blastocyst. These cells give rise to the embryo and ultimately the fetus. The ICM cells are used to generate embryonic stem cells. Multipotent — Ability of a single stem cell to develop into more than one cell type of the body. See also pluripotent and totipotent. Neurons — Nerve cells, the structural and functional unit of the nervous system. A neuron consists of a cell body and its processes — an axon and one or more dendrites. Neurons function by starting and conducting impulses. Neurons transmit impulses to other neurons or cells by releasing neurotransmitters at synapses. Pluripotent — Ability of a single stem cell to give rise to all of the various cell types that make up the body. Pluripotent cells cannot make so-called "extra-embryonic" tissues such as the amnion, chorion, and other components of the placenta. Proliferation — Expansion of cells by the continuous division of single cells into two identical daughter cells. Regenerative medicine — A treatment in which stem cells are induced to differentiate into the specific cell type required to repair damaged or destroyed cell populations or tissues. (See also cell-based therapies). Reproductive cloning — The goal of reproductive cloning is to create an animal that is identical to the animal that donated the somatic cell nucleus. The embryo is implanted in a uterus and develops into a live being. The first animal to be created by reproductive cloning was Dolly the sheep, born at the Roslin Institute in Scotland in 1996. See also Somatic cell nuclear transfer (SCNT). Somatic cell — any body cell other than gametes (egg or sperm). See also Gamete. Somatic cell nuclear transfer (SCNT) — A technique that combines an unfertilized enucleated egg (nucleus removed) and the nucleus of a somatic cell to make a nuclear transfer product or blastocyst. SCNT is the scientific term for cloning. SCNT can be used for therapeutic or reproductive purposes, but the initial stage that combines an enucleated egg and a somatic cell nucleus is the same. See also therapeutic cloning and reproductive cloning. Somatic stem cells — Non-embryonic stem cells that are not derived from gametes (egg or sperm cells). Stem cells — Cells with the ability to divide for long periods and to give rise to specialized cells, often many different types of specialized cells. Therapeutic cloning — The goal of therapeutic cloning is to create cells that exactly match a patient. By combining a patient's somatic cell nucleus and an enucleated egg, a scientist may harvest embryonic stem cells from the resulting nuclear transfer product that can be used to generate tissues that match a patient's body. This means the tissues created are unlikely to be rejected by the patient's immune system. See also Somatic cell nuclear transfer (SCNT). Totipotent — A totipotent stem cell can give rise to all the cell types that make up the body plus all of the cell types that make up the extraembryonic tissues such as the placenta. (See also Pluripotent and Multipotent). Umbilical cord blood stem cells — stem cells collected from the umbilical cord at birth that can produce all of the blood cells in the body (hematopoietic). Cord blood is currently used to treat patients who have undergone chemotherapy to destroy their bone marrow due to cancer or other blood-related disorders. Page Citation: In Stem Cell Information [World Wide Web site]. Bethesda , MD : National Institutes of Health, U.S. Department of Health and Human Services, 2006. Available at <http://stemcells.nih.gov/info/glossary>.
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