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Radiation
therapy: The local use of radiation to destroy cancer cells or
stop them from dividing and growing.
Radiographic anatomy: Diagnostic branch of anatomy that includes the use
of x-rays.
Rami
communicantes: Branches of a spinal nerve. Singular is
ramus communicans.
Randomized controlled trial (RCT): A clinical trial that involves
at least one test treatment and one control treatment, in which the
treatments administered are selected by a random process (e.g., coin flips
or a random-numbers table).
Randomized design: 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.
RDA:
Recommended dietary allowance. Set by the Food and Nutrition Board of the
Institute of Medicine, the RDA is the average daily dietary intake level
sufficient to meet the nutrient requirements of nearly all (97-98%) healthy
individuals in a specific life stage and gender group (e.g., women from
19-50 years of age). It is intended as a goal for daily intake of specific
nutrients by individuals.
Reactivity: Ability of an antigen to react specifically with the
antibody whose formation it induced.
Reactive
oxygen species (ROS): Highly reactive chemicals, containing
oxygen, that react easily with other molecules, resulting in potentially
damaging modifications.
Reactive
nitrogen species (RNS): Highly reactive chemicals, containing
nitrogen, that react easily with other molecules, resulting in potentially
damaging modifications.
Receptor:
A protein on or protruding from the cell surface to which select chemicals
can bind. Binding of a specific molecule (ligand) may result in a cellular
signal, or the internalization of the receptor and the ligand.
Recessive
trait: A trait that is expressed only when two copies of the gene
responsible for the trait are present.
Rectum:
The last section of the large intestine (colon). It connects the sigmoid
colon (above) to the anus (below).
Redox
reaction: 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).
Reduction:
A chemical reaction in which a molecule or atom gains electrons.
Renal:
Refers to the kidneys.
Resorption: The process of breaking down or assimilating
something. With respect to bone, resorption refers to the breakdown of bone
by osteoclasts that results in the release of calcium and phosphate (bone
mineral) into the blood.
Response
element: 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.
Retina:
The sensory membrane that lines most of the back of the eye. The retina is
composed of several layers including one containing the rods and cones. It
receives the image formed by the lens and converts it into chemical and
nervous signals which reach the brain by way of the optic nerve.
Rheumatoid arthritis: An autoimmune disease which causes chronic
inflammation of the joints, the tissue around the joints, as well as other
organs in the body. Because it can affect multiple other organs of the body,
rheumatoid arthritis is a systemic illness and is sometimes called
rheumatoid disease.
Riboucelotide: A molecule consisting of a 5-carbon sugar (ribose),
a nitrogen containing base, and one or more phosphate groups.
Rickets:
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 a impaired incorporation of calcium and
phosphate into the skeleton.
RNA:
Ribonuceic acid. a chain of nucleotides, which are composed of a
nitrogen containing base, a 5-carbon sugar (ribose), and phosphate groups.
RNA functions in the translation of the genetic information in DNA to
protein synthesis.
Ruminant:
An
animal that chews cud. Ruminant animals include cattle, goats, sheep, and
deer.
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