a mixture of equal amounts of isomers that are mirror images of each other (enantiomers).
the local use of radiation to destroy cancer cells or stop them from dividing and growing.
Randomized controlled trial (RCT)
a clinical trial with at least one active treatment group and a control (placebo) group. In RCTs, participants are chosen for the experimental and control groups at random and are not told whether they are receiving the active or placebo treatment until the end of the study. This type of study design can provide evidence of causality.
an experiment in which participants are chosen for the experimental and control groups at random, in order to reduce bias caused by self-selection into experimental and control groups. This type of study design can provide evidence of causality.
recommended dietary allowance. Established by the Food and Nutrition Board of the US Institute of Medicine, the RDA is the average daily dietary intake level of a nutrient sufficient to meet the requirements of nearly all healthy individuals in a specific life stage and gender group.
Reactive nitrogen species (RNS)
highly reactive chemicals, containing nitrogen, that react easily with other molecules, resulting in potentially damaging modifications.
Reactive oxygen species (ROS)
highly reactive chemicals, containing oxygen, that react easily with other molecules, resulting in potentially damaging modifications.
a type of measurement error caused by inaccuracies in the recollection of study participants regarding past behaviors and experiences.
a specialized molecule inside or on the surface of a cell that binds a specific chemical (ligand). Ligand binding usually results in a change in activity within the cell.
a trait that is expressed only when two copies of the gene responsible for the trait are present.
the last portion of the large intestine, connecting the sigmoid colon (above) to the anus (below). The rectum stores stool until it is evacuated from the body.
another term for an oxidation-reduction reaction. A redox reaction is any reaction in which electrons are removed from one molecule or atom and transferred to another molecule or atom. In such a reaction one substance is oxidized (loses electrons) while the other is reduced (gains electrons).
an amount of a reducing compound that donates the equivalent of one mole of electrons or hydrogen ions in a redox reaction.
a chemical reaction in which a molecule or atom gains electrons.
a rapid process of cell growth by which the epidermis repairs itself after a wounding event. The goal of reepithelialization is to re-establish a functional barrier that protects underlying cells from environmental exposures.
Relative Risk (RR)
the probability of a negative outcome in the exposed group divided by the probability of the negative outcome in the non-exposed (control) group.
refers to the kidneys.
in nutrition, having fulfilled nutrient requirements.
results when investigators fail to completely control for confounders by adjustment in statistical analyses.
a single unit within a polymer, such as an amino acid within a protein.
the process of breaking down or assimilating something. With respect to bone, resorption refers to the breakdown of bone by osteoclasts, resulting in the release of calcium and phosphate (bone mineral) into the blood.
a sequence of nucleotides in a gene that can be bound by a protein. Proteins that bind to response elements in genes are sometimes called transcription factors or binding proteins. Binding of a transcription factor to a response element regulates the production of specific proteins by inhibiting or enhancing the transcription of genes that encode those proteins.
with respect to the coronary arteries, restenosis refers to the reocclusion of a coronary artery after it has been dilated using coronary angioplasty.
the nerve layer that lines the back of the eye. In the retina, images created by light are converted to nerve impulses, which are transmitted to the brain via the optic nerve.
an epidemiological study that looks back in time. A retrospective study begins after the exposure and the disease have occurred. Most case-control studies are retrospective.
a chronic autoimmune disease characterized by inflammation of the synovial lining of the joints. Rheumatoid arthritis may also affect other organs of the body, including the skin, eyes, lungs, and heart.
a molecule consisting of a five-carbon sugar (ribose), a nitrogen-containing base, and one or more phosphate groups.
often the result of vitamin D deficiency. Rickets affects children while their bones are still growing. It is characterized by soft and deformed bones and is the result of an impaired incorporation of calcium and phosphate into the skeleton.
the probability of a negative outcome occurring.
ribonucleic acid; a single-stranded nucleic acid composed of many nucleotides. The nucleotides in RNA are composed of a nitrogen-containing base (adenine, guanine, cytosine, or uracil), a five-carbon sugar (ribose) and a phosphate group. RNA functions in the translation of the genetic information encoded in DNA to proteins.
the first part of the stomach of a ruminant.
an animal that chews cud. Ruminant animals include cattle, goats, sheep, and deer.
Saturated fatty acid
a fatty acid with no double bonds between carbon atoms.
Scavenge (free radicals)
to combine readily with free radicals, preventing them from reacting with other molecules.
a debilitating brain disorder that affects about 1% of the world’s population. Symptoms may include hallucinations, delusions, thought disorders, disorders of movement, cognitive deficits, lack of emotional expression, or impaired ability to speak, plan, and interact with others. Although its cause is not known, schizophrenia is thought to result from a combination of genetic and environmental factors.
a disorder caused by lack of vitamin C. Symptoms include anemia, bleeding gums, tooth loss, joint pain, and fatigue. Scurvy is treated by supplying foods high in vitamin C, as well as with vitamin C supplements.
gland found at the base of hair follicles that secretes sebum.
a sebum-producing cell in the skin.
a waxy/oily substance secreted by mammals that coats the outer layer of the skin.
uncontrolled electrical activity in the brain, which may produce a physical convulsion, minor physical signs, thought disturbances, or a combination of symptoms.
plaques made by deposits of ß-amyloid peptides in Alzheimer’s disease.
5-hydroxytryptamine. Serotonin is a neurotransmitter that may also function as a vasoconstrictor (substance that causes blood vessels to narrow).
whole blood without clotting factors. Serum is separated from blood cells using a centrifuge. Unlike plasma, serum lacks clotting factors because it is obtained from blood that has been allowed to clot.
Short bowel syndrome
a malabsorption syndrome resulting from the surgical removal of an extensive portion of the small intestine.
Sickle cell anemia
a hereditary disease in which a mutation in the gene for one of the proteins that comprises hemoglobin results in the formation of defective hemoglobin molecules known as hemoglobin S. Individuals who are homozygous for this mutation (possess two genes for hemoglobin S) have red blood cells that change from the normal discoid shape to a sickle shape when the oxygen supply is low. These sickle-shaped cells are easily trapped in capillaries and damaged, resulting in severe anemia. Individuals who are heterozygous for the mutation (possess one gene for hemoglobin S and one normal hemoglobin gene) have increased resistance to malaria.
a group of anemias that are all characterized by the accumulation of iron deposits in the mitochondria of immature red blood cells. These abnormal red blood cells do not mature normally, and many are destroyed in the bone marrow before reaching the circulation. Sideroblastic anemias can be hereditary, idiopathic (unknown cause), or caused by such diverse factors as certain drugs, alcohol, or copper deficiency.
Signal transduction pathway
a cascade of events that allows a signal outside a cell to result in a functional change inside the cell. Signal transduction pathways play important roles in regulating numerous cellular functions in response to changes in a cell’s environment.
a sleep disorder characterized by repeated cessation of breathing.
the part of the digestive tract that extends from the stomach to the large intestine. The small intestine includes the duodenum (closest to the stomach), the jejunum, and the ileum (closest to the large intestine).
capable of being dissolved.
the polyol (sugar alcohol) corresponding to glucose.
the formation and development of mature spermatozoa.
the mature male reproductive cell.
a birth defect, also known as a neural tube defect, resulting from failure of the lower end of the neural tube to close during embryonic development. Spina bifida, the most common cause of infantile paralysis, is characterized by a lack of protection of the spinal cord by its membranes and vertebral bones.
intercellular edema in the epidermis.
also known as celiac sprue and celiac disease, it is an inherited disease in which the intestinal lining is inflamed in response to the ingestion of a protein known as gluten. Treatment of celiac disease involves the avoidance of gluten, which is present in many grains, including wheat, rye, oats, and barley. Inflammation and atrophy of the lining of the small intestine leads to impaired nutrient absorption.
the state of nutrition of an individual with respect to a specific nutrient. Diminished or low status indicates inadequate supply or stores of a specific nutrient for optimal physiological functioning.
the accumulation of fat in the liver.
obstruction or narrowing of a passage. Coronary stenosis refers specifically to obstruction or narrowing of a coronary artery, which supplies blood to the heart muscle (myocardium).
a molecule related to cholesterol. Many important hormones, such as estrogen and testosterone, are steroids.
Steroid hormone receptor
a protein within a cell which binds to a specific steroid hormone. Binding of the steroid hormone changes the shape of the receptor protein and activates it, allowing it to activate gene transcription. In this way, a steroid hormone can activate the synthesis of specific proteins.
the outer layer of skin; consists of corneocytes that are connected by various proteins and lipids to form a tight barrier around underlying tissue.
a hairline or microscopic break in a bone, usually due to repetitive stress rather than trauma. Stress fractures are usually painful, and may be undetectable by X-ray. Although they may occur in almost any bone, common sites of stress fractures are the tibia (lower leg) and metatarsals (foot).
damage that occurs to a part of the brain when its blood supply is suddenly interrupted (ischemic stroke) or when a blood vessel ruptures and bleeds into the brain (hemorrhagic stroke). A stroke is also called a cerebrovascular accident (CVA).
without clinical signs or symptoms; sometimes used to describe the early stage of a disease or condition, before symptoms are detectable by clinical examination or laboratory tests.
under the skin.
a reactant in an enzyme-catalyzed reaction.
a nutrient or phytochemical supplied in addition to that which is obtained in the diet.
cell-cell junction that allows chemical or electrical signals to be passed from a neuron to another neuron or muscle cell.
the ability of neurons to change the number or strength of their synaptic connections. Synaptic plasticity is believed to underlie the processes of learning and memory.
a combination of symptoms that occur together and is indicative of a specific condition or disease.
when the effect of two treatments together is greater than the sum of the effects of the two individual treatments, the effect is said to be synergistic.
the formation of a chemical compound from its elements or precursor compounds.
a structured review of the literature designed to answer a clearly formulated question. Systematic reviews use systematic and explicitly predetermined methods to identify, select and critically evaluate research relevant to the question, and to collect and analyze data from the studies that are included in the review. Statistical methods, such as meta-analysis, may be used to summarize the results of the included studies.
Systemic lupus erythematosus (SLE)
a chronic autoimmune disease characterized by inflammation of the connective tissue. SLE is more common in women than men and may result in inflammation and damage to the skin, joints, blood vessels, lungs, heart, and kidneys.
Systolic blood pressure
the highest arterial pressure measured during the heart beat cycle, and the first number in a blood pressure reading (e.g., 120/80).