A-B C D-F G-H I-M N-O P-Q R-S T-Z
Natural killer (NK) cells
cytotoxic lymphocytes important for the innate immune response that kills pathogens. NK cells also have important roles in killing cancer cells.
Necrosis
unprogrammed cell death, in which cells break open and release their contents, promoting inflammation. Necrotic cell death may be the result of injury, infection, or infarction.
Neoplasm
a term referring to a rapid and abnormal growth of tissue. Neoplasms can be benign or malignant.
Nephropathy
kidney damage or disease.
Nerve impulse
the electrochemical signal transmitted in the cell membrane of a neuron or muscle cell. Also called action potential.
Nested case-control study
a case-control study within a cohort study; cases of a disease that occur in a defined cohort are identified, and a specified number of matched controls is then selected from the larger cohort for comparison.
Neural Tube Defect (NTD)
a birth defect caused by abnormal development of the neural tube, the structure which gives rise to the central nervous system. Neural tube defects include anencephaly and spina bifida.
Neurodegenerative disease
disease resulting from the degeneration or deterioration of nerve cells (neurons). Alzheimer’s disease and Parkinson’s disease are neurodegenerative diseases.
Neurologic
or neurological; involving nerves or the nervous system (brain, spinal cord, and all sensory and motor nerves).
Neuron
cell of the nervous system that conducts nerve impulses. Also called nerve cell.
Neuropathy
nerve damage or disease.
Neurotoxic
toxic or damaging to nervous tissue (brain and peripheral nerves).
Neurotransmitter
a chemical that is released from a nerve cell and results in the transmission of an impulse to another nerve cell or organ (e.g., a muscle). Acetylcholine, dopamine, norepinephrine, and serotonin are neurotransmitters.
Neutrophil
white blood cell that internalizes and destroys pathogens, such as bacteria. Neutrophils are also called polymorphonuclear leukocytes because they are white blood cells with multi-lobed nuclei.
NIH
US National Institutes of Health. Administered under the US Department of Health and Human Services (HHS), the NIH are more than 20 separate institutes and centers devoted to medical research.
Nitric oxide
a gaseous signaling molecule synthesized from the amino acid arginine by enzymes called nitric oxide synthases. In the vascular endothelium, nitric oxide promotes arterial vasodilation.
Nucleic acid
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid); long polymer of nucleotides.
Nucleosome
repeating unit of chromatin that consists of DNA that is coiled around histones.
Nucleotide
subunit of nucleic acids. Nucleotides are composed of a nitrogen-containing base (adenine, guanine, cytosine, uracil, or thymine), a five-carbon sugar (ribose or deoxyribose), and one or more phosphate groups.
Nucleus
a membrane-bound cellular organelle, which contains DNA organized into chromosomes.
Obesity
a condition of increased body fat; defined as a body mass index (BMI) =30 for adults.
Observational study
a study in which no experimental intervention or treatment is applied. Participants are simply observed over time.
Ocular
relating to the eye.
Odds ratio (OR)
a measure of association comparing the odds of an outcome in the exposed group to the odds of an outcome in the non-exposed (control) group. The OR is an approximation of the relative risk.
Omega-3 index
the amount of eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) in red blood cell membranes expressed as the percent of total red blood cell membrane fatty acids.
Oncology
the field of medicine dealing with cancer and tumors.
One-carbon unit
a biochemical term for functional groups containing only one carbon in addition to other atoms. One-carbon units transferred by folate coenzymes include methyl (-CH3), methylene (-CH2-), formyl (-CH=O), formimino (-CH=NH), and methenyl (-CH=). Many biosynthetic reactions involve the addition of a one-carbon unit to a precursor molecule.
Open-label trial
a clinical trial in which the investigators and participants are aware of the treatment (i.e., it is not double-blind).
Optimum health
in addition to freedom from disease, the ability of an individual to function physically and mentally at his or her best.
Organelle
a specialized component of a cell, such as the mitochondrian or lysosome, so named because they are analogous to organs.
Organic
refers to carbon-containing compounds, generally synthesized by living organisms.
Oropharynx
a term used to describe the mouth and throat.
Osteoarthritis
a degenerative joint condition that is characterized by the breakdown of articular cartilage (cartilage within the joint).
Osteoblast
bone cell that is responsible for the formation of new bone mineral in the bone remodeling process.
Osteoclast
bone cell that is responsible for the breakdown or resorption of bone in the bone remodeling process.
Osteocyte
a type of bone cell formed from an osteoblast once it becomes embedded deep within the organic matrix.
Osteomalacia
a disease of adults that is characterized by softening of the bones due to loss of bone mineral. Osteomalacia is characteristic of vitamin D deficiency in adults, while children with vitamin D deficiency suffer from rickets.
Osteonecrosis
death of bone tissue.
Osteopenia
a condition of low bone mass clinically defined as having a T-score one to 2.5 standard deviations (SD) below that of the average young adult (30 years of age) female.
Osteoporosis
a condition of increased bone fragility and susceptibility to bone fracture due to a loss of bone mineral density (BMD)
Overnutrition
a form of malnutrition where nutrients are supplied in excess of the body’s needs.
Oxidant
reactive oxygen species.
Oxidation
a chemical reaction that removes electrons from an atom or molecule.
Oxidative damage
damage to cells caused by reactive oxygen species.
Oxidative stress
a condition, in which the effects of pro-oxidants (e.g., free radicals, reactive oxygen and reactive nitrogen species) exceed the ability of antioxidant systems to neutralize them.