Glossary
739
recognition
binding of antigen to receptor
specifi c for that antigen on lymphocyte surface
recombinant DNA
(re-KOM-bih-nent) DNA
formed by joining portions of two DNA
molecules previously fragmented by a
restriction enzyme
recruitment
activation of additional cells in
response to increased stimulus strength;
increasing the number of active motor units in
a muscle
rectum
short segment of large intestine between
sigmoid colon and anus
red muscle fi
ber
muscle fi ber having high
oxidative capacity and large amount of
myoglobin
refl
ex
(REE-fl ex) biological control system linking
stimulus with response and mediated by a
refl ex arc
refl
ex arc
neural or hormonal components that
mediate a refl ex; usually includes receptor,
afferent pathway, integrating center, efferent
pathway, and effector
refl
ex response
fi nal change due to action of
stimulus upon refl ex arc; also called
effector
response
refractory period
(reh-FRAK-tor-ee) time
during which an excitable membrane does not
respond to a stimulus that normally causes
response;
see also
absolute refractory period,
relative refractory period
regulatory site
site on protein that interacts with
modulator molecule; alters functional site
properties
relative refractory period
time during which
excitable membrane will produce action
potential, but only to a stimulus of greater
strength than the usual threshold strength
relaxation
return of muscle to a low force-
generating state, caused by detachment of
cross-bridges
relaxin
hormone secreted by the ovary before
parturition
releasing hormone
see
hypophysiotropic hormone
REM sleep
(rem) sleep state associated with small,
rapid EEG oscillations, complete loss of tone
in postural muscles, and dreaming; also called
rapid eye movement sleep, paradoxical sleep
renal
(REE-nal) pertaining to kidneys
renal corpuscle
combination of glomerulus and
Bowman’s capsule
renal cortex
outer portion of the kidney
renal medulla
inner portion of the kidney
renal pelvis
cavity at base of each kidney; receives
urine from collecting duct system and empties
it into ureter
renal plasma fl
ow
the total amount of plasma
(blood minus red cell volume) that passes
through both kidneys per unit time
renal tubule
fl uid-fi lled tube extending from
the renal corpuscle; site of renal fl uid and
electrolyte exchange
renin
(REE-nin) peptide secreted by kidneys;
acts as an enzyme that catalyzes splitting off of
angiotensin I from angiotensinogen in plasma
renin-angiotensin system
hormonal system
consisting of renin-stimulated angiotensin
I production followed by conversion to
angiotensin II by angiotensin-converting
enzyme
replicate
(REP-lih-kayt) duplicate
repolarize
return transmembrane potential to its
resting level
residual volume (RV)
air volume remaining in
lungs after maximal expiration
resistance (R)
hindrance to movement through a
particular substance, tube, or opening
respiration
(cellular) oxygen utilization
in metabolism of organic molecules;
(respiratory system) oxygen and carbon
dioxide exchange between organism and
external environment
respiratory acidosis
increased arterial H
+
concentration due to carbon dioxide retention
respiratory alkalosis
decreased arterial H
+
concentration when carbon dioxide elimination
from the lungs exceeds its production
respiratory bronchiole
largest branch of the
respiratory tree in which the units of gas
exchange (alveoli) appear
respiratory cycle
changes in the lung volumes
from the beginning of an inspiration, including
the expiration, to the beginning of the next
inspiration
respiratory pump
mechanism whereby reductions
in intrathoracic pressure during the breathing
cycle tend to favor the return of blood to the
heart from peripheral veins
respiratory quotient (RQ)
ratio of carbon
dioxide produced to oxygen consumed during
metabolism
respiratory rate
number of breaths per minute
respiratory rhythm generator
neural network
in the brainstem that generates output to the
phrenic nerve
respiratory zone
portion of airways from
beginning of respiratory bronchioles to alveoli;
contains alveoli across which gas exchange
occurs
resting membrane potential
voltage difference
between inside and outside of cell in absence of
excitatory or inhibitory stimulation; also called
resting potential
rest-or-digest
homeostatic state characteristic of
parasympathetic nervous system activation
restriction element
see
MHC protein
retching
strong involuntary attempt to vomit but
without stomach contents passing through
upper esophageal sphincter
rete testes
(REE-tee TES-teez) network of canals
at the ends of the seminiferous tubules in the
testes
reticular activating system
extensive neuron
network extending through brainstem core;
receives and integrates information from
many afferent pathways and from other CNS
regions
reticulocyte
(ruh-TIK-you-low-site) name
given to immature red blood cells that have
a weblike pattern in the cytosol due to the
persistence of ribosomes
retina
thin layer of neural tissue lining back of
eyeball; contains receptors for vision
retinal
(ret-in-AL) form of vitamin A that forms
chromophore component of photopigment
retrograde
movement of a substance or action
potential backward along a neuron, from
axon terminals toward the cell body and
dendrites
reuptake
active process that recaptures excess
secreted neurotransmitter back into the
presynaptic cell; can be inhibited with drugs
reversible reaction
chemical reaction in which
energy release is small enough for reverse
reaction to occur readily;
compare
irreversible
reaction
Rh factor
group of erythrocyte plasma-membrane
antigens that may (Rh
+
) or may not (Rh
) be
present
rhodopsin
(roh-DOP-sin) photopigment in rods
ribonucleic acid (RNA)
(ry-boh-noo-KLAY-
ik) single-stranded nucleic acid involved in
transcription of genetic information and
translation of that information into protein
structure; contains the sugar ribose;
see also
messenger RNA, ribosomal RNA, transfer
RNA
ribose
the sugar backbone of RNA
ribosomal RNA (rRNA)
(ry-boh-SOME-al)
type of RNA used in ribosome assembly;
becomes part of ribosome
ribosome
(RY-boh-some) cytoplasmic particle
that mediates linking together of amino acids
to form proteins; attached to endoplasmic
reticulum as bound ribosome, or suspended in
cytoplasm as free ribosome
right and left bundle branch
see
bundle branch
rigor mortis
(RIG-or MOR-tiss) stiffness of
skeletal muscles after death due to failure of
cross-bridges to dissociate from actin because
of the loss of ATP
RNA polymerase
(POL-ih-muh-rase) enzyme that
forms RNA by joining together appropriate
nucleotides after they have base-paired to DNA
rod
one of two receptor types for photic energy;
contains the photopigment rhodopsin
rough endoplasmic reticulum
see
endoplasmic
reticulum
round window
membrane-covered opening in
the cochlea that responds to fl uid movement in
the scala tympani
ryanodine receptor
calcium-release channel
found in the lateral sacs of the sarcoplasmic
reticulum in skeletal muscle cells
S
saccade
(sah-KADE) short, jerking eyeball
movement
saccule
structure in the semicircular canals that
responds to changes in linear movement of the
head by mechanical forces on otoliths located
on its surface
saliva
watery solution of salts and proteins,
including mucins and amylase, secreted by
salivary glands
salivary gland
one of three pairs of exocrine
glands around the mouth that produce saliva
salt appetite
desire for salt, consisting of
hedonistic and regulatory components
saltatory conduction
propagation of action
potentials along a myelinated axon such that
the action potentials jump from one node of
Ranvier in the myelin sheath to the next
sarcomere
(SAR-kuh-meer) repeating structural
unit of myofi bril; composed of thick and thin
fi laments; extends between two adjacent Z lines
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