G-18 Glossarytroponin (tro 9 p ̆o-nin) A protein found in the thin
filaments of the sarcomeres of skeletal muscle. A
subunit of troponin binds to Ca^21 , and as a result
causes tropomyosin to change position in the thin
filament.
trypsin (trip 9 sin) A protein-digesting enzyme
in pancreatic juice that is released into the small
intestine.
tryptophan (trip 9 t ̆o-f ̄an) An amino acid that also
serves as the precursor for the neurotransmitter
molecule serotonin.
TSH thyroid-stimulating hormone Also called
thyrotropin (thi 0 r ̆o-tro 9 pin). A hormone secreted
by the anterior pituitary that stimulates the thyroid
gland.
tubuloglomerular (too 0 by ̆u-lo-glo-mer 9 y ̆u-
lar) feedback A control mechanism whereby an
increased flow of fluid through the nephron tubules
causes a reflex reduction in the glomerular filtration
rate.
tumor necrosis (n ̆e-kro 9 sis) factor (TNF)
A cytokine released by immune cells and mast cells
that causes destruction of tumors and migration of
neutrophils toward the site of a bacterial infection.
TNF is also secreted by adipose cells and may be a
paracrine regulator of insulin sensitivity.
turgid (tur 9 jid) Swollen and congested.
twitch A rapid contraction and relaxation of a
muscle fiber or a group of muscle fibers.
tympanic (tim-pan 9 ik) membrane The eardrum;
a membrane separating the external from the middle
ear that transduces sound waves into movements of
the middle-ear ossicles.
tyrosine kinase (ti 9 r ̆o-sen ki 9 n ̄as) An enzyme that
adds phosphate groups to tyrosine, an amino acid
present in most proteins. The membrane receptor
for insulin, for example, is a tyrosine kinase. When
bound to insulin, the tyrosine kinase is activated,
which leads to a cascade of effects that mediate
insulin’s action.U
universal donor A person with blood type O, who
is able to donate blood to people with other blood
types in emergency blood transfusions.
universal recipient A person with blood type AB,
who can receive blood of any type in emergency
transfusions.
upper motor neurons Neurons in the brain that,
as part of the pyramidal or extrapyramidal system,
influence the activity of the lower motor neurons in
the spinal cord.
urea (yoo-re- ̆a) The chief nitrogenous waste
product of protein catabolism in the urine, formed in
the liver from amino acids.
uremia (yoo-re 9 me- ̆a) The retention of urea and
other products of protein catabolism as a result of
inadequate kidney function.
urobilinogen (yoo 0 r ̆o-bi-lin 9 ̆o-jen) A compound
formed from bilirubin in the intestine. Some is
excreted in the feces and some is absorbed and
enters the enterohepatic circulation where it may be
excreted either in the bile or in the urine.V
vaccination (vaks 0 s ̆ı-na 9 shun) The clinical
induction of active immunity by introducing antigens
into the body so that the immune system becomes
sensitized to them. The immune system will mount
a secondary response to those antigens upon
subsequent exposures.titin The largest protein the human body, titin
extends from a Z disc of a sarcomere to its M line.
The springlike portion of titin contributes to muscle
elasticity.
tolerance, immunological The ability of the
immune system to distinguish self from nonself;
thus, the immune system does not normally attack
those antigens that are part of one’s own tissues.
tonicity (to-nis 9 i-te) The osmotic pressure of a
solution in comparison to the pressure of another
solution, usually blood plasma. Solutions with the
same osmotic pressure are isotonic; those with a
lower osmotic pressure are hypotonic; and those with
a higher osmotic pressure are hypertonic.
total minute volume The product of tidal volume
(ml per breath) and ventilation rate (breaths per
minute).
totipotent (t ̄otip 9 ̆o-tent) The ability of a cell to
differentiate into all tissue types, and thus to form
a new organism when appropriately stimulated and
placed in the correct environment (a uterus).
toxin (tok 9 sin) A poison.
toxoid (tok 9 soid) A modified bacterial endotoxin
that has lost toxicity but that still has the ability to act
as an antigen and stimulate antibody production.
tracts A collection of axons within the central
nervous system that forms the white matter of the
CNS.
transamination (trans 0 am- ̆ı-na 9 shun) The transfer
of an amino group from an amino acid to an alpha-
keto acid, forming a new keto acid and a new amino
acid without the appearance of free ammonia.
transferrin (trans-fer 9 in) A protein in the plasma
that binds to and transports iron, so that the iron
component of hemoglobin in destroyed red blood
cells can be recycled back to the bone marrow for the
synthesis of new hemoglobin.
transcription (tran-skrip 9 shun), genetic The
process by which messenger RNA is synthesized
from a DNA template resulting in the transfer of
genetic information from the DNA molecule to the
mRNA.
transducins (trans-doo 9 sinz) The G-proteins
involved in vision. When light causes the
photodissociation of rhodopsin, the G-protein alpha
subunit dissociates from the opsin and indirectly
causes a reduction in the dark current of the
photoreceptors.
translation (trans-la 9 shun), genetic The process
by which messenger RNA directs the amino acid
sequence of a growing polypeptide during protein
synthesis.
transplantation (trans 0 plan-ta 9 shun) The grafting
of tissue from one part of the body to another part, or
from a donor to a recipient.
transport maximum Abbreviated Tm, the
maximum rate at which a substance can be
transported by a carrier protein across a plasma
membrane. At the transport maximum, the carriers
are said to be saturated.
transpulmonary (trans 0 pul 9 m ̆o-ner 0 -e) pressure
The pressure difference across the wall of the lung;
equal to the difference between intrapulmonary
pressure and intrapleural pressure.
triglyceride (tri-glis 9 er-id) Fats and oils. Also
known as triacylglycerol.
triiodothyronine (tri 0 i- ̆o 9 d ̆o-thi 9 ro-n ̄en) (T 3 )
A hormone secreted in small amounts by the thyroid;
the active hormone in target cells formed from
thyroxine.
tropomyosin (tro 0 p ̆o-mi 9 ̆o-sin) A filamentous
protein that attaches to actin in the thin filaments.
Together with another protein called troponin, it
acts to inhibit and regulate the attachment of myosin
cross bridges to actin.polymerase during DNA replication. This inability
to copy telomeres may contribute to cell aging and
death. Germinal cells (that produce gametes) and
cancer cells have an additional enzyme, telomerase,
which copies the telomeres.
telophase (tel 9 ̆o-f ̄az) The last step of mitosis and
the last step of the second division of meiosis.
tendon (ten 9 dun) The dense regular connective
tissue that attaches a muscle to the bones of its origin
and insertion.
testes (tes 9 t ̄ez); sing; testis. Male gonads. Testes
are also known as testicles.
testis-determining factor (TDF) The product of a
gene located on the short arm of the Y chromosome
that causes the indeterminate embryonic gonads to
develop into testes.
testosterone (tes-tos 9 t ̆e-r ̄on) The major androgenic
steroid secreted by the Leydig cells of the testes after
puberty.
tetanus (tet 9 n-us) In physiology, a term used to
denote a smooth, sustained contraction of a muscle,
as opposed to muscle twitching.
tetraiodothyronine (tet 0 r ̄a-i 0 ̆oo-d ̆o-thi 9 ro-n ̄en)
(T 4 ) A hormone containing four iodine atoms; also
known as thyroxine.
thalassemia (thal 0 ̆a-se 9 me- ̆a) Any of a group
of hemolytic anemias caused by the hereditary
inability to produce either the alpha or beta chain
of hemoglobin. It is found primarily among
Mediterranean people.
theophylline (the-of 9 ̆ı-lin) A drug found in certain
tea leaves that promotes dilation of the bronchioles
by increasing the intracellular concentration of cyclic
AMP (cAMP) in the smooth muscle cells. This effect
is due to inhibition of the enzyme phosphodiesterase,
which breaks down cAMP.
thermiogenesis (ther-me-o-jen 9 ̆ı-sis) The
production of heat by the body through mechanisms
such as increased metabolic rate.
thorax (thor 9 aks) The part of the body cavity
above the diaphragm; the chest.
threshold The minimum stimulus that just
produces a response.
thrombin (throm 9 bin) A protein formed in blood
plasma during clotting that enzymatically converts
the soluble protein fibrinogen into insoluble fibrin.
thrombocyte (throm 9 b ̆o-s ̄ıt) A blood platelet; a
disc-shaped structure in blood that participates in clot
formation.
thrombopoietin (throm 0 bo-poi-e 9 tin) A cytokine
that stimulates the production of thrombocytes (blood
platelets) from megakaryocytes in the bone marrow.
thrombosis (throm-bo 9 sis) The development or
presence of a thrombus.
thrombus (throm 9 bus) A blood clot produced by
the formation of fibrin threads around a platelet plug.
thymus (thi 9 mus) A lymphoid organ located in
the superior portion of the anterior mediastinum. It
processes T lymphocytes and secretes hormones that
regulate the immune system.
thyroglobulin (thi-ro-glob 9 y ̆u-lin) An iodine-
containing protein in the colloid of the thyroid
follicles that serves as a precursor for the thyroid
hormones.
thyroxine (thi-rok 9 sin) Also called
tetraiodothyronine, or T 4. The major hormone
secreted by the thyroid gland. It regulates the basal
metabolic rate and stimulates protein synthesis in
many organs. A deficiency of this hormone in early
childhood produces cretinism.
tinnitus (t ̆ı-ni 9 tus) The spontaneous sensation of a
ringing sound or other noise without sound stimuli.
tissue factor A membrane glycoprotein that
initiates the extrinsic pathway of blood clotting; also
called thromboplastin or factor III.fox36375_glo_G1-G19.indd 18fox36375_glo_G1-G19.indd 18 2/4/15 12:29 PM2/4/15 12:29 PM