Glossary 585Teratogen(te-RAH-toh-jen) Anything that causes devel-
opmental abnormalities in an embryo; may be a chemical
or microorganism to which an embryo is exposed by way
of the mother (Chapter 21).
Testes(TES-teez) (Sing.—testis) The male gonads that
produce sperm cells; also endocrine glands that secrete
the hormone testosterone (Chapter 10).
Testosterone (tes-TAHS-ter-ohn) The sex hormone
secreted by the interstitial cells of the testes; responsible
for the maturation of sperm, growth of the male repro-
ductive organs, and the secondary sex characteristics
(Chapter 10).
Tetanus(TET-uh-nus) 1. A sustained contraction of a
muscle fiber in response to rapid nerve impulses; the
basis for all useful movements. 2. A disease, characterized
by severe muscle spasms, caused by the bacterium
Clostridium tetani(Chapter 7).
Thalamus(THAL-uh-muss) The part of the brain superior
to the hypothalamus; regulates subconscious aspects of
sensation (Chapter 8).
Theory(THEER-ree) A statement that is the best explana-
tion of all the available evidence on a particular process
or mechanism. A theory is nota guess (Chapter 3).
Thoracic cavity(thaw-RASS-ik KAV-i-tee) Part of the
ventral cavity, superior to the diaphragm (Chapter 1).
Thoracic duct(thaw-RASS-ik DUKT) The lymph vessel
that empties lymph from the lower half and upper left
quadrant of the body into the left subclavian vein
(Chapter 14).
Thoracic vertebrae(thaw-RASS-ik VER-te-bray) The 12
vertebrae that articulate with the ribs (Chapter 6).
Threshold level–renal (THRESH-hold LE-vuhl) The
concentration at which a substance in the blood notnor-
mally excreted by the kidneys begins to appear in the
urine; for several substances, such as glucose, in the renal
filtrate, there is a limit to how much the renal tubules can
reabsorb (Chapter 18).
Thrombocyte(THROM-boh-sight) Platelet; a fragment
of a megakaryocyte (Chapter 11).
Thrombocytopenia (THROM-boh-SIGH-toh-PEE-
nee-ah) An abnormally low platelet count (Chapter 11).
Thrombopoietin(THROM-boh-POY-e-tin) A hormone
produced by the liver that stimulates development of
megakaryocytes in the red bone marrow (Chapter 11).
Thrombus(THROM-bus) A blood clot that obstructs
blood flow through a blood vessel (Chapter 11).
Thymus(THIGH-mus) An organ made of lymphatic tissue
located inferior to the thyroid gland; large in the fetus
and child, and shrinks with age; produces T cells and
hormones necessary for the maturation of the immune
system (Chapter 14).
Thyroid cartilage(THIGH-roid KAR-ti-ledj) The largest
and most anterior cartilage of the larynx; may be felt in
the front of the neck (Chapter 15).
Thyroid gland(THIGH-roid) An endocrine gland on theanterior side of the trachea below the larynx; secretes
thyroxine, triiodothyronine, and calcitonin (Chapter 10).
Thyroid-stimulating hormone (TSH) A hormone
secreted by the anterior pituitary gland that causes the
thyroid gland to secrete triiodothyronine and thyroxine
(Chapter 10).
Thyroxine(T 4 ) (thigh-ROK-sin) A hormone secreted by
the thyroid gland that increases energy production and
protein synthesis (Chapter 10).
Tibia(TIB-ee-yuh) The larger long bone of the lower leg
(Syn.—shinbone) (Chapter 6).
Tidal volume(TIGH-duhl VAHL-yoom) The volume of
air in one normal inhalation and exhalation; average:
400–600 mL (Chapter 15).
Tissue(TISH-yoo) A group of cells with similar structure
and function (Chapter 1).
Tissue fluid(TISH-yoo FLOO-id) The water found in
intercellular spaces. Also called interstitial fluid (Chap-
ter 2).
Tissue macrophage system(TISH-yoo MAK-roh-fayj)
The organs or tissues that contain macrophages that
phagocytize old red blood cells: the liver, spleen, and red
bone marrow (Chapter 11).
Tissue typing(TISH-yoo TIGH-ping) A laboratory pro-
cedure that determines the HLA types of a donated
organ, prior to an organ transplant (Chapter 11).
Titin(TIGH-tin) The protein in sarcomeres that anchors
myosin filaments to the Z lines (Chapter 7).
Tongue(TUHNG) A muscular organ on the floor of the
oral cavity; contributes to chewing and swallowing and
contains taste buds (Chapter 16).
Tonsillectomy (TAHN-si-LEK-toh-mee) The surgical
removal of the palatine tonsils and/or adenoid (Chapter
14).
Tonsils(TAHN-sills) The lymph nodules in the mucosa of
the pharynx, the palatine tonsils, and the adenoid; also
the lingual tonsils on the base of the tongue (Chapter 14).
Toxin(TAHK-sin) A chemical that is poisonous to cells
(Chapter 22).
Toxoid(TAHK-soyd) An inactivated bacterial toxin that is
no longer harmful yet is still antigenic; used as a vaccine
(Chapter 14).
Trace element (TRAYS EL-uh-ment) Those elements
(minerals) needed in very small amounts by the body for
normal functioning (Chapter 2).
Trachea(TRAY-kee-ah) The organ that is the air passage-
way between the larynx and the primary bronchi (Syn.—
windpipe) (Chapter 15).
Transamination(TRANS-am-i-NAY-shun) The transfer
of an amino (NH 2 ) group from an amino acid to a carbon
chain to form a non-essential amino acid; takes place in
the liver (Chapter 16).
Transcription(tran-SKRIP-shun) The process by which a
complementary copy, mRNA, is made of a DNA gene;
will be followed by translation (Chapter 3).30Scanlon(p3) Glossary 8/17/06 11:08 AM Page 585