730
Glossary
integral membrane protein
protein embedded
in membrane lipid layer; may span entire
membrane or be located at only one side
integrating center
cells that receive one or more
signals and send out appropriate response;
also called an
integrator
integrin
(in-TEH-grin) transmembrane
protein in plasma membrane; binds to
specifi c proteins in extracellular matrix and
on adjacent cells to help organize cells into
tissues
intercalated disk
(in-TER-kuh-lay-tid) structure
connecting adjacent cardiac myocytes,
having components for tensile strength
(desmosomes) and low-resistance electrical
pathways (gap junctions)
intercellular cleft
a narrow, water-fi lled space
between capillary endothelial cells
intercellular fl
uid
fl uid that lies between cells;
also called interstitial fl uid
intercostal muscle
(in-ter-KOS-tal) skeletal
muscle that lies between ribs and whose
contraction causes rib cage movement during
breathing
interferon
(in-ter-FEER-on) family of proteins
that nonspecifi cally inhibit viral replication
inside host cells; interferon-gamma also
stimulates the killing ability of macrophages
and NK cells
interferon-gamma
see
interferon
interleukin
(in-ter-LOO-kin) a family of
cytokines with many effects on immune
responses and host defenses
interleukin 1 (IL-1)
cytokine secreted by
macrophages and other cells that activates
helper T cells, exerts many infl ammatory
effects, and mediates many of the systemic,
acute-phase responses, including fever
interleukin 2 (IL-2)
cytokine secreted by
activated helper T cells that causes antigen-
activated helper T, cytotoxic T, and NK
cells to proliferate; also causes activation of
macrophages
interleukin 6 (IL-6)
cytokine secreted by
macrophages and other cells that exerts
multiple effects on immune system cells,
infl ammation, and the acute-phase response
intermediate fi
lament
actin-containing fi lament
associated with desmosomes
internal anal sphincter
smooth-muscle ring
around lower end of rectum
internal environment
extracellular fl uid
(interstitial fl uid and plasma)
internal genitalia
(jen-ih-TAY-lee-ah)
see
female
internal genitalia
internal urethral sphincter
(you-REE-thrul)
part of smooth muscle of urinary bladder wall
that opens and closes the bladder outlet
internal work
energy-requiring activities in body;
see also
work;
compare
external work
interneuron
neuron whose cell body and axon lie
entirely in CNS
interstitial fl
uid
extracellular fl uid surrounding
tissue cells; excludes plasma
interstitium
(in-ter-STISH-um) interstitial space;
fl uid-fi lled space between tissue cells
interventricular septum
the muscular wall
separating the right and left ventricles of the
heart
intestinal phase
(of gastrointestinal control)
initiation of neural and hormonal
gastrointestinal refl exes by simulation of
intestinal tract walls
intestino-intestinal refl
ex
cessation of
contractile activity in intestines in response to
various stimuli in intestine
intracellular fl
uid
fl uid in cells; cytosol plus
fl uid in cell organelles, including nucleus
intrafusal fi
ber
modifi ed skeletal muscle fi ber in
muscle spindle
intrapleural fl
uid
(in-trah-PLUR-al) thin fl uid
fi lm in thoracic cavity between pleura lining
the inner wall of thoracic cage and pleura
covering lungs
intrapleural pressure (
P
ip
)
pressure in pleural
space; also called
intrathoracic pressure
intrarenal baroreceptor
pressure-sensitive
juxtaglomerular cells of afferent arterioles,
which respond to decreased renal arterial
pressure by secreting more renin
intrathoracic pressure
see
intrapleural
pressure
intrinsic
(in-TRIN-sik) situated entirely within
a part
intrinsic factor
glycoprotein secreted by
stomach epithelium and necessary for
absorption of vitamin B
12
in the ileum
intrinsic pathway
intravascular sequence of
fi brin clot formation initiated by factor XII
or, more usually, by the initial thrombin
generated by the extrinsic clotting pathway
intrinsic tone
spontaneous low-level contraction
of smooth muscle, independent of neural,
hormonal, or paracrine input
intron
(IN-trahn) regions of noncoding
nucleotides in a gene
inulin
polysaccharide that is fi ltered but not
reabsorbed, secreted, or metabolized in the
renal tubules; used to measure glomerular
fi ltration rate
inversely proportional
relationship in which, as
one factor increases by a given amount, the
other decreases by a given amount
iodide trapping
active transport of iodide
from plasma across the thyroid follicular cell
membrane, followed by diffusion of iodide
into the colloid of the follicle
iodine
chemical found in certain foods and as
an additive to table salt; concentrated by the
thyroid gland, where it is incorporated into
the structure of thyroid hormone
ion
(EYE-on) atom or small molecule containing
unequal number of electrons and protons and
therefore carrying a net positive or negative
electric charge
ionic bond
(eye-ON-ik) strong electrical
attraction between two oppositely charged
ions
ionization
(eye-on-ih-ZAY-shun) process of
removing electrons from or adding them to
an atom or small molecule to form an ion
ionotropic receptor
(eye-ohn-uh-TROPE-
ik) membrane protein through which ionic
current is controlled by the binding of
extracellular signaling molecules
ipsilateral
(ip-sih-LAT-er-al) on the same side of
the body
iris
ringlike structure surrounding pupil of eye
irreversible reaction
chemical reaction that
releases large quantities of energy and results
in almost all the reactant molecules being
converted to product;
compare
reversible
reaction
ischemia
(iss-KEY-me-ah) reduced blood supply
islet of Langerhans
(EYE-let of LAN-ger-
hans) cluster of pancreatic endocrine cells;
distinct islet cells secrete insulin, glucagon,
somatostatin, and pancreatic polypeptide
isometric contraction
(eye-soh-MET-rik)
contraction of muscle under conditions in
which it develops tension but does not change
length
isoosmotic
(eye-soh-oz-MAH-tik) having the
same total solute concentration as extracellular
fl uid
isotonic
(eye-soh-TAH-nik) containing the same
number of effectively nonpenetrating solute
particles as normal extracellular fl uid;
see also
isotonic contraction
isotonic contraction
contraction of muscle
under conditions in which load on the muscle
remains constant but muscle changes length
isotope
an atom consisting of one or more
additional neutrons than protons in its nucleus
isovolumetric ventricular contraction
(eye-soh-
vol-you-MET-rik) early phase of systole when
atrioventricular and aortic valves are closed and
ventricular size remains constant
isovolumetric ventricular relaxation
early
phase of diastole when atrioventricular and
aortic valves are closed and ventricular size
remains constant
J
JAK kinase
cytoplasmic kinase bound to a
receptor but not intrinsic to it
jejunum
(jeh-JU-num) middle segment of small
intestine
J receptor
receptor in the lung capillary walls or
interstitium that responds to increased lung
interstitial pressure
junctional feet
see
foot process
juxtaglomerular apparatus (JGA)
(jux-tah-gloh-
MER-you-lar) renal structure consisting of
macula densa and juxtaglomerular cells; site of
renin secretion and sensors for renin secretion
and control of glomerular fi ltration rate
juxtaglomerular (JG) cell
renin-secreting cells in
the afferent arterioles of the renal nephron in
contact with the macula densa
juxtamedullary nephron
functional unit of the
kidney with glomeruli in the deep cortex and
a long loop of Henle, which plunges into the
medulla
K
kallikrein
(KAL-ih-cryn) an enzyme produced by
gland cells that catalyzes the conversion of the
circulating protein kininogen into the signaling
molecule bradykinin
karyotype
chromosome characteristics of a cell,
usually visualized with a microscope
keto acid
a class of breakdown products formed
from the deamination of amino acids
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