970
GLOSSARY
reactant
(re-ak
tant)
A chemical that
takes part in a chemical reaction. A
starting material. p. 58
receptor
(re
sep
tor)
Specialized cells
that provide information about the
environment. Also, cell surface
structures that bind particular
molecules, called ligands, thereby
transmitting a signal to inside the
cell. pp. 9, 80
receptor-mediated endocytosis
(re
sep
tor-me
de-a
¯-tid en
do-
si-to
sis)
Selective uptake of
molecules into a cell by binding to a
speciF c receptor. p. 97
recessive allele
(re-ses
iv ah-le
¯l)
±orm
of a gene not expressed if the
dominant form is present. p. 920
recruitment
(re-kro
¯o
¯t
ment)
Increase
in number of motor units activated
as stimulation intensity increases.
p. 298
rectum
(rek
tum)
Terminal end of the
digestive tube between the sigmoid
colon and the anus. p. 687
red blood cell
(red blud sel)
Disc-
shaped cell, lacking a nucleus, that
is packed with the oxygen-carrying
molecule hemoglobin; erythrocyte.
p. 162
red marrow
(red mar
o)
Blood cell-
forming tissue in bones. p. 203
red f
ber
(red F
ber)
Slow-contracting
postural muscle F
ber that contains
abundant myoglobin. p. 299
reFerred pain
(re-ferd
pa
¯n)
Pain that
feels as if it is originating from a part
other than the site being stimulated.
p. 441
refl
ex
(re
fl eks)
Rapid, automatic
response to a stimulus. p. 389
refl
ex arc
(re
fl eks ark)
Nerve pathway,
consisting of a sensory neuron,
interneuron, and motor neuron, that
forms the structural and functional
bases for a refl
ex. p. 389
reFraction
(re-frak
shun)
Bending of
light as it passes between media of
different densities. p. 471
reFractory period
(re-frak
to-re pe
re-od)
Period following stimulation during
which a neuron or muscle F
ber
will not respond to a stimulus.
p. 370
renal
(re
nal)
Pertaining to the kidney.
p. 776
renal corpuscle
(re
nal kor
pusl)
Part
of a nephron that consists of a
glomerulus and a glomerular capsule;
Malpighian corpuscle. p. 779
renal cortex
(re
nal kor
teks)
Outer part
of a kidney. p. 776
renal medulla
(re
nal me
˘-dul
ah)
Inner
part of a kidney. p. 776
puberty
(pu
ber-te)
Stage of
development in which the
reproductive organs become
functional. p. 846
pulmonary circuit
(pul
mo-ner
e ser
kit)
System of blood vessels that carries
blood between the heart and the
lungs. p. 553
pulmonary valve
(pul
mo-ner
e valv)
Valve leading from the right
ventricle to the pulmonary trunk
(artery); pulmonary semilunar valve.
p. 557
pulse
(puls)
Surge of blood felt through
the walls of arteries due to the
contraction of the heart ventricles.
p. 582
Punnett square
(pun
it skwair)
A
grid diagram that displays possible
progeny that can be predicted based
on parental gametes. p. 920
pupil
(pu
pil)
Opening in the iris
through which light enters the eye.
p. 467
purine
(pu re
¯n)
Type of nitrogen-
containing base that is part of DNA
and RNA and has two organic rings;
adenine and guanine. p. 126
Purkinje f
bers
(pur-kin
je F
berz)
Specialized muscle F
bers that
conduct the cardiac impulse from
the AV bundle into the ventricular
walls. p. 567
pyloric sphincter
(pi-lor
ik sF
ngk
ter)
Ring of muscle between the stomach
and the duodenum; controls food
entry into the duodenum. p. 666
pyridoxine
(pir
ı˘-dok
se
¯n)
A vitamin
of the B-complex group; vitamin B
6
.
p. 715
pyrimidine
(pe-ri
mı˘-de
¯n)
Type of
nitrogen-containing base that is
part of DNA and RNA and has two
organic rings; thymine, cytosine, and
uracil. p. 126
pyruvic acid
(pi-roo
vik as
id)
Intermediate product of
carbohydrate oxidation. p. 120
R
radiation
(ra
de-a
shun)
±orm of
energy that includes visible light,
ultraviolet light, and X rays; the
means by which body heat is lost as
infrared rays. pp. 53, 182
radioactive
(ra
de-o-ak
tiv)
Property
of an atom that releases energy at a
constant rate. p. 53
rate-limiting enzyme
(ra
¯t lim
ı˘-ting
en
zı¯m)
Enzyme, usually present
in small amounts, that controls
the rate of a metabolic pathway by
regulating one of its steps. p. 118
progenitor cell
(pro-jen
ı˘-tor sel)
Daughter cell of a stem cell whose
own daughter cells are restricted to
follow speciF
c lineages. p. 105
progesterone
(pro-jes
te
˘-ro
¯n)
±emale
hormone secreted by the corpus
luteum of the ovary and the
placenta. p. 857
projection
(pro-jek
shun)
Process by
which the brain causes a sensation
to seem to come from the region of
the body being stimulated. p. 439
prolactin
(pro-lak
tin)
Hormone
secreted by the anterior pituitary
gland that stimulates the production
of milk in the mammary glands;
PRL. p. 495
pronation
(pro-na
shun)
Downward or
backward rotation of the palm.
p. 269
prophase
(pro
fa
¯z)
Stage of mitosis
when chromosomes become visible
when stained and viewed under a
microscope. p. 101
proprioceptor
(pro
pre-o-sep
tor)
Nerve
ending that senses changes in
muscle or tendon tension. p. 439
prostaglandins
(pros
tah-glan
dins)
Group of compounds that have
powerful, hormonelike effects. p. 491
prostate gland
(pros
ta
¯t gland)
Gland
surrounding the male urethra below
the urinary bladder that secretes
into semen prior to ejaculation.
p. 801
protein
(pro
te
¯n)
Nitrogen-containing
organic compound composed of
bonded amino acid molecules. p. 64
protein buFFer system
(pro
te
¯n buf
er
sis
tem)
Amino acids of a protein
accept or donate hydrogen ions to
keep the concentration of hydrogen
ions in solution constant; resists
changes in pH. p. 821
protein kinase
(pro
te
¯n ki
na
¯s)
Enzyme
that catalyzes the reaction to form a
phosphoprotein. p. 488
prothrombin
(pro-throm
bin)
Plasma
protein that functions in blood
clotting. p. 539
proton
(pro
ton)
Positively charged
particle in an atomic nucleus. p. 52
protraction
(pro-trak
shun)
±orward
movement of a body part. p. 269
provitamin
(pro-vi
tah-min)
Precursor
of a vitamin. p. 709
proximal
(prok
sı˘-mal)
Closer to the
trunk or origin; opposite of distal.
p. 21
pseudostratif
ed
(soo
do-strat
ı˘-fı¯d)
Single layer of epithelial cells that
appear as more than one layer
because the nuclei occupy different
positions in the cells. p. 146
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