Cells: the individual unit that makes up all of the tissues of the body. All living things are made up of one or more cells. (NCIt)

The basic structural and functional units of which living "organisms" and “tissues” are composed, usually microscopic and consisting of “cytoplasm” bounded by a “membrane,” with “genetic material” contained in a “nucleus.” (Oxford) In plants and animals, each cell has internal order, and the cells within the body have specific arrangements and functions. (Brooker, 3) Each cell contains all of the “chromosomes” of the organism and therefore all of the “genes” necessary to form the entire organism. Cell types are unique however, because in each cell type only some of those genes are turned on (“expressed”). All of the other genes are shut off (“repressed"). (Kandel, 257) A cell that is ‘determined’ has a particular cell fate. A cell that is “differentiated” has a specialized “morphology” and function. (Brooker, 411) One function of living cells is to act as organic factories that produce “proteins.” "Nerve cells" allow us to respond to “stimuli” in the “environment,” process that information, and act. These cells are of different types, each distinctive in its structure and function. We can investigate the overall structure of a cell as a source of insight into its work. (Kolb, 76) Adjective - 'cellular.'

Apoptosis: cell death. Necessary to produce certain features of the body. Basic cell process to create tissues and “organs.” (Brooker, 203) The body's normal method of disposing of damaged, unwanted, or unneeded cells. (HGPIA) A series of molecular steps in a cell lead to its death. This is one method the body uses to get rid of unneeded or abnormal cells. The process of apoptosis may be blocked in cancer cells. (NCI1) The process of programmed cell death. It is used during early development to eliminate unwanted cells; for example, those between the fingers of a developing hand. In adults, apoptosis is used to rid the body of cells that have been damaged beyond repair. Every day, five hundred billion "blood cells" die in an individual human. We all shed about five hundred million skin cells every day. We shed our entire outer layer of skin every two to four weeks. (Venter, 41) When “neurons” are deprived of a “neurotrophic factor,” certain genes seem to be turned on, resulting in a message for the cell to die. (Kolb, 200) Apoptosis also plays a role in preventing cancer. If apoptosis is for some reason prevented, it can lead to uncontrolled cell division and the subsequent development of a tumor. (NHGRI) Also referred to as ‘programmed cell death.’

Cell Cycle: the process a cell goes through each time it divides. The cell cycle consists of a series of steps during which the "chromosomes" and other cell material double to make two copies. The cell then divides into two "daughter cells," each receiving one copy of the doubled material. The cell cycle is complete when each daughter cell is surrounded by its own outer membrane. (PubMedHealth2) Has two major stages - "interphase" and "mitosis." A cell spends most of its time in interphase, and during this time it grows, replicates its chromosomes, and prepares for cell division. The cell then leaves interphase, undergoes mitosis, and completes its division. The resulting cells daughter cells each enter their own interphase and begin a new round of the cell cycle. (NHGRI) (Cells) have an ‘internal clock’ (referred to as) 'telomere shortening' that tells them approximately how many times to divide. (Lewis, 31) Also referred to as 'mitotic cycle.'

Cell Lineage: the developmental history of specific differentiated cell types as traced back to the original stem cells in the embryo. (MeSH)

Cell Theory: all organisms are made of cells. (Brooker, 3) All modern cells come from pre-existing cells by division. (Brooker, 106) The idea that plant and animal bodies are mode up of cells, and that the cell is the unit structure of an organism. First Proposed by Theodore Schwann for animals in 1838-40. (Lawrence) Also referred to as ‘cell doctrine.’

Cellular Adhesion: adherence of cells to surfaces or to other cells. (MeSH) The "binding" of a cell to another cell, as in tissues, or to "extracellular matrix," mediated by cell-surface molecules. (Lawrence) Precise sequence of interactions among proteins that connect cells. “Inflammation” is one type of cellular adhesion. (Lewis, 36) The close adherence (bonding) to adjoining cell surfaces. (NCI1)

Compartmentalization: a characteristic of cells that is defined by many organelles that separate the cell into different regions. Cellular compartmentalization allows a cell to carry out specialized chemical reactions in different places. (Brooker, G-8) Adjective - ‘compartmental.’

Diploid Cell: a full set of genetic material consisting of paired chromosomes, one from each parental set. Most animal cells except the "gametes" have a diploid set of chromosomes. The diploid human genome has 46 chromosomes. (HGPIA) A cell that carries two sets of chromosomes. (Brooker, G-11) (Most) human cells are diploid with two sets of chromosomes, each set with 23 chromosomes, for a total of 46. They include one set of chromosomes from the mother and one set of chromosomes from the father. (Norman, 7/8/09)

Eukaryote Cell(s): any cell from a member of the Eukarya domain. (Lawrence) Large cells up to 50 "micrometers" in diameter. (Have) many membrane-surrounded “organelles,” such as “mitochondria.” (Have) an internal arrangement of “microtubules.” A defining distinction between “prokaryotic” and eukaryotic cells is that eukaryotic cells have a cell nucleus in which the genetic material is surrounded by a “membrane.” (Indge, 102) Also referred to as ‘eukaryote.’

Extracellular: situated or occurring outside a cell. (Oxford) Any structures that are not enclosed “intracellularly” are considered extracellular structure, including structures on the cell surface. (NCIt) Secreted by or diffused outside of the cell. (Lawrence)

Extracellular Fluid: the fluid in an organism’s body that is outside of the cells. (Brooker, G-14) The fluid in the spaces between cells and in the "vascular" system. (Lawrence) Every cell in a multicellular organism is surrounded by an oily “membrane” that separates it from other cells and from the extracellular fluid that bathes all cells. (Kandel, 58)

Extracellular Matrix (ECM): a network of material that is secreted from cells and forms a complex meshwork outside of cells. The ECM provides strength, support, and organization. (Brooker, G-14) Holds cells together. Promotes cellular proliferation and provides a supporting structure to which cells adhere. It is broken down during normal physiological and disease processes such as bone ‘remodeling,’  “embryogenesis,”  “cancer,” and “arthritis.” (MeSH) In the skin of mammals, the strength of the ECM prevents tearing. The ECM found in “cartilage” resists compression and provides protection to the “joints.” Protects the soft parts of the body, such as internal organs. The skeletons of many animals are composed primarily of ECM. Contains a mixture of several different components, including proteins such as “collagen,” that form fibers. (Brooker, 192)

Extracellular Space: the space between cells. Accounts for up to a 20 percent of the volume inside our brains. (In the brain) filled with "cerebrospinal fluid," the same liquid that surrounds and cushions the brain and spinal cord. Conditions producing a lack of oxygen, such as stroke, shrink the extracellular space. As the space constricts, the diffusion of substances between cells slows, and toxic substances are concentrated, impeding recovery. Aging has the same effect, and the shrinkage may be linked to learning. (SAM Oct/Nov07, 8)

Haploid Cell: a cell containing one set of chromosomes. (Brooker, G-16) A single set of chromosomes (half the full set of genetic material) present in the egg and sperm cells of animals, and in the egg and pollen cells of plants. Human beings have 23 chromosomes in their reproductive cells. (HGPIA) Human gametes are haploid, with one set of 23 chromosomes, for a total of 23 chromosomes.  Includes "sperm" and "egg cells." (Norman, 7/8/09)

Host Cell: a cell that is infected by a "virus" or another type of "microorganism." (NCI1)

Intercellular: among or between cells. (Lawrence)

Intercellular Junction: direct contact of a cell with a neighboring cell. (MeSH)

Intracellular: situated or occurring within a, or the, cell or cells. (Oxford) Inside a cell. (NCIt) The area within cells. (MeSH)

Multicellular: having, consisting of, or involving, several or many cells. (Oxford) A ‘multicellular process’ is a biologic function or process involving groups or populations of single cell types, mixed cell types, or tissues. (NCIt)

Progenitor Cell: cell that  gives rise to other types of cells. (Lawrence) Cell derived from a “stem cell.” ("Neural" progenitor cells) migrate and produce a “neuron” or a “glial cell.” (Kolb, 194)

Somatic Cells: body (cells) as opposed to "germ cells." Will not produce gametes. (Lawrence) Include "bone," "nerve," and "muscle," and subtypes of these. Have two copies of the "genome" and are said to be diploid. (There are) more than 260 differentiated cell types. (Lewis, 19) Also referred to as 'body cells.'

Stem Cells: cells from which other types of cells develop. For example, “blood cells" develop from blood-forming stem cells. (NCI1) All cells in the human body descend from stem cells. (Lewis, 38) A cell with the potential to form many of the different cell types found in the body. When stem cells divide, they can form more stem cells or other cells that perform specialized functions. Stem cells continue to divide as long as the individual remains alive. (NHGRI) Undifferentiated, primitive cells... that have the ability both to multiply and to "differentiate" into specific blood cells. (HGPIA) Have two common characteristics. First, they have the capacity to divide, and second, their daughter cells can differentiate into one or more specialized cell types. (Brooker, 403) Scientists are investigating ways to coax human stem cells into becoming replacement cells for people with diseases. (GNN) Also referred to as ‘progenitor cells’ and ‘mother cells.’

Precursor Stem Cells: capable of giving rise to a particular and limited set of different cell types. (Lawrence) Specialized stem cells that are committed to give rise to cells that have a particular function; examples are 'myeloid progenitor' cells; and skin stem cells. (MeSH) Can divide, eventually producing non-dividing cells known as ‘neuroblasts’ and ‘glioblasts’ that mature into “neurons” and “glia.” (Kolb, 194) Also referred to as ‘multipotent stem cells’ and ‘precursors.’

Adult Stem Cells: cells with high proliferative and self renewal capacities derived from adults. (MeSH) Occur in many tissues and organs, including bone marrow, muscle, liver, pancreas, etc., and can produce the specialized cells needed in the particular tissue or organ in which they arise. (OxfordMed) Found in the tissues of fetuses, embryos, children, and adults. Self renew, but most are ‘multipotent,’ giving rise to a few types of specialized daughter cells. (Lewis, 39) Adult stem cells can only form certain types of specialized cells. (NHGRI)

Neural Stem Cells: self-renewing cells that generate the main “phenotypes” of the “nervous system” in both the embryo and adult. Neural stem cells are “precursors” to both neurons and glia. (MeSH) As neural stem cells proliferate they give rise to to neural stem cells and to neural precursors that can grow up to be either neurons or glial cells. They divide periodically in two main areas: the “ventricles”, and the “hippocampus.” Have (also) been found in “olfactory bulbs.” (Best of the Brain-Fred Gage, 123) A self-renewing, multi-potential cell that gives rise to any of the different types of neurons and glia in the nervous system. (Their) presence has only been recently confirmed in adults. Has an extensive capacity for self-renewal. (In addition to self-renewal), they give rise to ‘precursor cells.’ (Kolb, 194) Neurons are born as blank-slate stem cells, and they go through a development process in which they need to find something to do in order to survive. (Ratey, 49)

Pluripotent Stem Cells: a cell... capable of developing or differentiating in any of various ways. (Oxford) Cells that are able to develop into many different types of cells or tissues in the body. (NCI1) Can give rise to cells of the three different germ layers. (MeSH) Also referred to as ‘pluripotent cells.’

Embryonic Stem Cells: an embryonic cell that can replicate indefinitely, transform into other types of cells, and serve as a continuous source of new cells. (HGPIA) Cells derived from the “blastocyst” which forms before implantation in the “uterine” wall. They retain the ability to divide, proliferate and provide “progenitor cells” that can differentiate into specialized cells. Can differentiate into almost any cell type. (OxfordMed) Give rise to all the cells of the body. (Lawrence) Embryonic stem cells have the potential to form a complete individual. (NHGRI) Not cells from an embryo. Created in a lab dish using cells from a region in a very early embryo called an ‘ICM.’ Come from ‘left-over’ embryos from fertility clinics that would otherwise by destroyed. (Lewis, 37)

Induced Pluripotent Stem Cells (iPS): cells from adult organisms that have been reprogrammed into a pluripotent state similar to that of embryonic stem cells. (MeSH) Cells that result from ‘reprogramming.’ Deriving iPS cells does not require the use of any cells from an embryo. (Currently) a research tool and not used to treat disease. (Lewis, 37)

Pluripotency: the potential of a cell to develop into more than one type of mature cell, depending on environment. (HGPIA)

Totipotent Stem Cells: cells capable of forming an cell type. In mammals the only genuinely totipotent cells are those are those of the embryonic "morula" stage. (Lawrence) Single cells that have the potential to form an entire organism. They have the capacity to specialize into ‘extra-embryonic’ membranes and tissues, the embryo, and all ‘post-embryonic’ tissues and organs. (MeSH) A fertilized egg is considered to be totipotent because it can produce all the cell types in the adult organism. (Brooker, 403)

Unicellular: having only one cell. (Lawrence) Consisting of a single cell. Characterized by the presence or formation of a single cell or cells. (Oxford)