Glossary
G-19
Reduction
Chemical reaction in which electrons and energy are gained by a
molecule (ofen accompanied by gain oF hydrogen ions) or oxygen is lost.
Referred pain
Pain Felt at a site other than the area oF origin.
Reflex
Automatic reaction to stimuli.
Refraction
Te bending oF a light ray when it meets a different surFace at
an oblique rather than right angle.
Regeneration
Replacement oF destroyed tissue with the same kind oF tissue.
Regulatory T cells (T
Reg
cells)
Population oF ± cells (usually expressing
CD4) that suppress the immune response.
Relative refractory period
²ollows the absolute reFractory period; interval
when a threshold For action potential stimulation is markedly elevated.
Renal
(re
9
nal) Pertaining to the kidney.
Renal autoregulation
Process the kidney uses to maintain a nearly constant
glomerular filtration rate despite fluctuations in systemic blood pressure.
Renal clearance
Te volume oF plasma From which a particular sub-
stance is completely removed in a given time, usually 1 minute; provides
inFormation about renal Function.
Renin
(re
9
nin) Enzyme released by the kidneys that raises blood pressure
by initiating the renin-angiotensin-aldosterone mechanism.
Rennin
Stomach-secreted enzyme that acts on milk protein; not pro-
duced in adults.
Repolarization
Movement oF the membrane potential to the initial rest-
ing (polarized) state.
Reproductive system
Organ system that Functions to produce offspring.
Resistance exercise
High-intensity exercise in which the muscles are pit-
ted against high resistance or immovable Forces and, as a result, muscle
cells increase in size.
Respiration
Te processes involved in supplying the body with oxygen
and disposing oF carbon dioxide.
Respiratory system
Organ system that carries out gas exchange; in-
cludes the nose, pharynx, larynx, trachea, bronchi, lungs.
Resting membrane potential
Te voltage that exists across the plasma
membrane during the resting state oF an excitable cell; ranges From
2
90
to
2
20 millivolts depending on cell type.
Reticular activating system (RAS)
(re-tik
9
u-lar) Diffuse brain stem
neural network that receives a wide variety oF sensory input and main-
tains wakeFulness oF the cerebral cortex.
Reticular connective tissue
Connective tissue with a fine network oF reticu-
lar fibers that Form the internal supporting Framework oF lymphoid organs.
Reticular formation
²unctional system that spans the brain stem; in-
volved in regulating sensory input to the cerebral cortex, cortical arousal,
and control oF motor behavior.
Reticular lamina
A layer oF extracellular material containing a fine
network oF collagen protein fibers; together with the basal lamina it is a
major component oF the basement membrane.
Reticulocyte
(rĕ-tik
9
u-lo-sīt) Immature erythrocyte.
Retina
(ret
9
ĭ-nah) Inner layer oF the eyeball; contains photoreceptors
(rods, cones).
Rhombencephalon (hindbrain)
(romb
0
en-seF
9
ah-lon) Caudal portion
oF the developing brain; constricts to Form the metencephalon and myel-
encephalon; includes the pons, cerebellum, and medulla oblongata.
Ribosomal RNA (rRNA)
A constituent oF ribosome; exists within the
ribosomes oF cytoplasm and assists in protein synthesis.
Ribosomes
(ri
9
bo-sōmz) Cytoplasmic organelles at which proteins are
synthesized.
Prothrombin time
Diagnostic test to determine status oF hemostasis
system.
Proton
(pro
9
ton) Subatomic particle that bears a positive charge; located
in the atomic nucleus.
Proton acceptor
A substance that takes up hydrogen ions in detectable
amounts. Commonly reFerred to as a base.
Proton donor
A substance that releases hydrogen ions in detectable
amounts; an acid.
Proximal
(prok
9
si-mul) ±oward the attached end oF a limb or the origin
oF a structure.
Pseudounipolar neuron
(soo
0
do-u
0
nĭ-po
9
lar) Another term For unipo-
lar neuron.
Puberty
Period oF liFe when reproductive maturity is achieved.
Pulmonary
(pul
9
muh-nayr-e) Pertaining to the lungs.
Pulmonary arteries
Vessels that deliver blood to the lungs to be oxygenated.
Pulmonary circuit
System oF blood vessels that serves gas exchange in
the lungs; i.e., pulmonary arteries, capillaries, and veins.
Pulmonary edema
(ĕ-de
9
muh) Leakage oF fluid into the air sacs and tis-
sue oF the lungs.
Pulmonary veins
Vessels that deliver Freshly oxygenated blood From the
respiratory zones oF the lungs to the heart.
Pulmonary ventilation
Breathing; consists oF inspiration and expiration.
Pulse
Rhythmic expansion and recoil oF arteries resulting From heart
contraction; can be Felt From outside the body.
Pupil
Opening in the center oF the iris through which light enters
the eye.
Pus
²luid product oF inflammation composed oF white blood cells, the
debris oF dead cells, and a thin fluid.
Pyloric sphincter
(pi-lor
9
ik sfink
9
ter) Valve oF the distal end oF the
stomach that controls Food entry into the duodenum.
Pyramidal (corticospinal) tracts
Major motor pathways concerned
with voluntary movement; descend From pyramidal cells in the Frontal
lobes oF each cerebral hemisphere.
Pyruvic acid
An intermediate compound in the metabolism oF carbohy-
drates.
Radioactivity
Te process oF spontaneous decay seen in some oF the
heavier isotopes, during which particles or energy is emitted From the
atomic nucleus; results in the atom becoming more stable.
Radioisotope
(ra
0
de-o-i
9
so-tōp) Isotope that exhibits radioactive
behavior.
Ramus
(ra
9
mus) Branch oF a nerve, artery, vein, or bone.
Rapid eye movement (REM) sleep
Stage oF sleep in which rapid eye
movements, an alert EEG pattern, and dreaming occur.
Reactant
A substance taking part in a chemical reaction.
Receptor
(re-sep
9
tor) (1) A cell or nerve ending oF a sensory neuron spe-
cialized to respond to particular types oF stimuli; (2) protein that binds
specifically with other molecules, e.g., neurotransmitters, hormones,
paracrines, antigens.
Receptor-mediated endocytosis
Te type oF endocytosis in which en-
gulFed particles attach to receptors beFore endocytosis occurs.
Receptor potential
A graded potential that occurs at a sensory receptor
membrane.
Recessive traits
A trait due to a particular allele that does not maniFest
itselF in the presence oF other alleles that generate traits dominant to it;
must be present in double dose to be expressed.
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