You’ve probably heard about stem cells in the news and may wonder exactly what that scientific term means. Stem cells are the body’s master cells. Stem cells can renew themselves (a process called self-renewal), and they can also make a variety of other kinds of cells.
Stem cells are either embryonic stem cells or adult stem cells. In the lab, embryonic stem cells keep reproducing themselves until they’re coaxed into creating specific types of cells. In the body, these cells eventually disappear, so a human adult body no longer contains cells that can generate any kind of cell — at least not in the normal course of things. (Scientists can manipulate adult cells to become other types of cells.)
The main difference between embryonic and adult stem cells is their type of potency. Here’s a breakdown of the differences:
Embryonic stem cells: Embryonic stem cells are derived from three- to five-day-old embryos that are created for fertilization treatments but aren’t going to be used to try to start a pregnancy; in other words, these blastocysts have never been implanted in a woman’s uterus and will be discarded if they aren’t used for research. IVF doctors culture a fertilized IVF embryo in a culture dish until it develops to the blastocyst stage. Researchers extract the inner cell mass, which is then used to derive embryonic stem cells.
Embryonic stem cells are pluripotent, meaning they can give rise to any type of cell in the fully developed body. (Embryonic stem cells can’t create the placenta or umbilical cord tissues, but they appear to be able to generate any other type of cell.)
Adult stem cells: So-called adult stem cells are really stem cells in specific tissues whose job seems to be replenishing their particular tissues — or specific parts of their tissues — as needed. Adult stem cells also renew themselves periodically to ensure that a pool of stem cells is always available to generate specific cell types. So far, scientists have verified stem cell caches in several tissues, including bone marrow, the brain, fatty tissue (called adipose tissue), the liver, the reproductive system (both male and female), skeletal muscles, skin, and teeth.
Adult stem cells are generally multipotent, able to give rise to several kinds of cells in their home tissues. However, in their normal environments, adult stem cells don’t seem to generate cell types outside their particular tissues. Liver stem cells, for example, don’t generate heart cells, and brain stem cells don’t generate kidney cells.
Stem cell researchers have developed a technique for reprogramming adult cells in the lab to get them to act more like embryonic stem cells. These reprogrammed cells are called induced pluripotent stem cells (iPS cells), and they can be made from adult cells in the skin, fatty tissue, and other sources.
Biology Glossary
anemia
A low number of red blood cells or low level of hemoglobin; may be caused by dietary deficiencies, metabolic disorders, hereditary conditions, or damaged bone marrow.
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antigen
A foreign substance in the body that causes an immune response.
Biology Glossary
body mass index
The BMI is the result of a formula that uses your weight and height to determine whether you need to lose weight.
Biology Glossary
carbohydrates
Energy-packed compounds consisting of carbon, hydrogen, and oxygen that provide quick fuel for organisms.
Biology Glossary
cellulose
A form of carbohydrate that has a structural role in living organisms (animals and plants).
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centrifuge
A machine that is used to separate blood cells and platelets from plasma.
Biology Glossary
chloroplasts
Plant cells that use energy from sunlight to create food.
Biology Glossary
cytoplasm
The fluid contained within animal cells. Also called plasma.
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disaccharides
Carbohydrate molecules in which 2 monosaccharide molecules are joined together. Disaccharides consist of 6 to 14 carbon atoms.
Biology Glossary
DNA
Stands for deoxyribonucleic acid. Large molecules found in all living things that carry genetic information.
Biology Glossary
electron microscope
A high-powered, expensive device that uses beams of electrons to bring the finest details of cells into focus.
Biology Glossary
endocrine system
A system of glands that secrete different types of hormones that help regulate organisms.
Biology Glossary
endoplasmic reticulum
The ER is a series of canals that connects the nucleus of animal cells to the cytoplasm outside those cells.
Biology Glossary
equilibrium
The state of a chemical reaction in which the amounts on each side of the reaction have stabilized.
Biology Glossary
eukaryotes
Organisms — including plants and animals, as well as fungi, protozoa, and most algae — with cells that contain a nucleus and chromosomes.
Biology Glossary
Golgi apparatus
A component within cells that packages and distributes hormones, enzymes, and other cell products to other organelles or outside the cell.
Biology Glossary
hemoglobin
An iron-containing molecule in red blood cells that carries oxygen around the body.
Biology Glossary
heterotrophs
Animals — including herbivores, carnivores, and omnivores — that feed on other living organisms.
Biology Glossary
homeostasis
The processes used by the body to constantly achieve and maintain balance.
Biology Glossary
integument
The skin or outer surface of an animal. Small animals such as earthworms use integumentary exchange to exchange gases with the environment.
Biology Glossary
Krebs cycle
A method of describing the steps involved in the chemical process of respiration.
Biology Glossary
lipoproteins
Compounds such as HDL and LDL that carry cholesterol through the bloodstream; made from a fat (lipid) and a protein.
Biology Glossary
lysosomes
Specialized cellular organelles formed by the Golgi apparatus that help to “clean up” the cell by breaking down harmful cell products and removing dead organelles.
Biology Glossary
maceration
A process, such as chewing, that physically breaks down food into pieces.
Biology Glossary
matrix
The extracellular fluid in which animal cells float.
Biology Glossary
mitochondria
An organelle in animal cells that combines food with oxygen to supply energy to cells.
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monosaccharides
Carbohydrate molecules in which simple sugars consist of three to seven carbon atoms.
Biology Glossary
nuclear membrane
A two-layer structure that separates the nucleus from the cytoplasm in animal cells.
Biology Glossary
organelles
Structures that float inside the fluid of cells; used during metabolic processes.
Biology Glossary
osmosis
A mechanism that moves water and nutrients into and throughout a plant.
Biology Glossary
peristalsis
The action of food being moved down the esophagus and through the entire digestive tract.
Biology Glossary
peroxisomes
Sacs of enzymes within animal cells that help protect the cell by breaking down accumulations of toxic products such as hydrogen peroxide.
Biology Glossary
photosynthesis
The biochemical process that plants use to acquire energy from the sun.
Biology Glossary
plasma membrane
The membrane that holds fluid within animal cells. Also called the cell membrane.
Biology Glossary
polysaccharides
Carbohydrate molecules that are formed by many long chains of monosaccharides.
Biology Glossary
prokaryotes
Organisms — such as bacteria and blue-green algae — with cells that do not contain a nucleus.
Biology Glossary
ribosomes
Components within cells that assist in making proteins from amino acids.
Biology Glossary
RNA
Stands for ribonucleic acid. In animals, works with DNA to produce proteins needed throughout the body.
Biology Glossary
ruminants
Mammals — such as cattle, sheep, and goats — that can break down and digest cellulose.
