Glossary 567Inguinal canal(IN-gwi-nuhl ka-NAL) The opening in the
lower abdominal wall that contains a spermatic cord in
men and the round ligament of the uterus in women; a
natural weak spot that may be the site of hernia forma-
tion (Chapter 20).
Inhibin(in-HIB-in) A protein hormone secreted by the sus-
tentacular cells of the testes and by the ovaries; inhibits
secretion of follicle-stimulating hormone (Chapter 10).
Inorganic(IN-or-GAN-ik) A chemical compound that does
not contain carbon–hydrogen covalent bonds; includes
water, salts, and oxygen (Chapter 1).
Insertion(in-SIR-shun) The more movable attachment
point of a muscle to a bone (Chapter 7).
Inspiration(in-spi-RAY-shun) Inhalation; the intake of air
to the lungs (Chapter 15).
Inspiratory reserve(in-SPYR-ah-tor-ee ree-ZERV) The
volume of air beyond tidal volume that can be inhaled
with the deepest inhalation; average: 2000–3000 mL
(Chapter 15).
Insulin(IN-syoo-lin) A protein hormone secreted by the
pancreas that decreases the blood glucose level by
increasing storage of glycogen and use of glucose by cells
for energy production (Chapter 10).
Integumentary system(in-TEG-yoo-MEN-tah-ree) The
organ system that consists of the skin and its accessory
structures and the subcutaneous tissue (Chapter 5).
Intensity(in-TEN-si-tee) The degree to which a sensation
is felt (Chapter 9).
Intercalated disc(IN-ter-kuh-lay-ted DISK) A modifica-
tion of the cell membrane of cardiac muscle cells; the end
membranes of adjacent cells are folded and fit into one
another; permits rapid transmission of the electrical
impulses that bring about contraction (Chapter 4).
Intercostal muscles(IN-ter-KAHS-tuhl MUSS-uhls) The
skeletal muscles between the ribs; the external inter-
costals pull the ribs up and out for inhalation; the inter-
nal intercostals pull the ribs down and in for a forced
exhalation (Syn.—spareribs) (Chapter 15).
Intercostal nerves(IN-ter-KAHS-tuhl NERVS) The pairs
of peripheral nerves that are motor to the intercostal
muscles (Chapter 15).
Interferon(in-ter-FEER-on) A chemical produced by T
cells or by cells infected with viruses; is part of innate
immunity and prevents the reproduction of viruses
(Chapter 14).
Internal(in-TER-nuhl) On the inside, or away from the
surface (Chapter 1).
Internal anal sphincter(in-TER-nuhl AY-nuhl SFINK-
ter) The circular smooth muscle that surrounds the anus;
relaxes as part of the defecation reflex to permit defeca-
tion (Chapter 16).
Internal respiration (in-TER-nuhl RES-pi-RAY-shun)
The exchange of gases between the blood in the systemic
capillaries and the surrounding tissue fluid and cells
(Chapter 15).Internal urethral sphincter(yoo-REE-thruhl SFINK-ter)
The smooth muscle sphincter at the junction of the uri-
nary bladder and the urethra; relaxes as part of the urina-
tion reflex to permit urination (Chapter 18).
Interneuron(IN-ter-NYOOR-on) A nerve cell entirely
within the central nervous system (Chapter 8).
Interphase(IN-ter-fayz) The period of time between
mitotic divisions during which DNA replication takes
place (Chapter 3).
Interstitial cells(in-ter-STISH-uhl SELLS) The cells in
the testes that secrete testosterone when stimulated by
LH (Chapter 20).
Intestinal glands(in-TESS-tin-uhl) 1. The glands of the
small intestine that secrete digestive enzymes. 2. The
glands of the large intestine that secrete mucus (Chapter
16).
Intracellular fluid(IN-trah-SELL-yoo-ler FLOO-id) The
water found within cells (Chapter 2).
Intramuscular injection(in-trah-MUSS-kew-ler in-JEK-
shun) An injection of a medication into a muscle
(Chapter 7).
Intrapleural pressure (in-trah-PLOOR-uhl) The pres-
sure within the potential pleural space; always slightly
below atmospheric pressure, about 756 mmHg (Chap-
ter 15).
Intrapulmonic pressure(in-trah-pull-MAHN-ik) The air
pressure within the bronchial tree and alveoli; fluctuates
below and above atmospheric pressure during breathing
(Chapter 15).
Intrinsic factor(in-TRIN-sik FAK-ter) A chemical pro-
duced by the parietal cells of the gastric mucosa; neces-
sary for the absorption of vitamin B 12 (Chapter 11).
Involuntary muscle (in-VAHL-un-tary MUSS-uhl)
Another name for smooth muscle tissue (Chapter 4).
Ion(EYE-on) An atom or group of atoms with an electrical
charge (Chapter 2).
Ionic bond(eye-ON-ik) A chemical bond formed by the
loss and gain of electrons between atoms (Chapter 2).
Iris(EYE-ris) The colored part of the eye, between the
cornea and lens; made of two sets of smooth muscle
fibers that regulate the size of the pupil, the opening in
the center of the iris (from the Latin “rainbow”) (Chapter
9).
Ischemic(iss-KEY-mik) Lack of blood to a body part, often
due to an obstruction in circulation (Chapter 12).
Ischium(ISH-ee-um) The lower posterior part of the hip
bone (Chapter 6).
Islets of Langerhans(EYE-lets of LAHNG-er-hanz) The
endocrine portions of the pancreas that secrete insulin
and glucagon (Syn.—pancreatic islets) (Chapter 10).
Isometric exercise (EYE-so-MEH-trik) Contraction of
muscles without movement of a body part (Chapter 7).
Isotonic(EYE-so-TAHN-ik) Having the same concentra-
tion of dissolved materials as the solution used as a com-
parison (Chapter 3).30Scanlon(p3) Glossary 8/17/06 11:08 AM Page 567