Glossary 551Arteriole(ar-TEER-ee-ohl) A small artery (Chapter 5).
Arteriosclerosis(ar-TIR-ee-oh-skle-ROH-sis) Deteriora-
tion of arteries with loss of elasticity that is often a con-
sequence of aging or hypertension; a contributing factor
to aneurysm or stroke (Chapter 13).
Artery(AR-tuh-ree) A blood vessel that takes blood from
the heart toward capillaries (Chapter 13).
Arthropod(AR-throw-pod) Invertebrate animals charac-
terized by an exoskeleton and jointed appendages;
includes insects, spiders, ticks, mites, and crustaceans
(Chapter 22).
Articular cartilage(ar-TIK-yoo-lar KAR-ti-lidj) The car-
tilage on the joint surfaces of a bone; provides a smooth
surface (Chapter 6).
Articulation(ar-TIK-yoo-LAY-shun) A joint (Chapter 6).
Ascites(a-SIGH-teez) An abnormal accumulation of fluid
in the peritoneal space (Chapter 15).
Asthma(AZ-mah) A respiratory disorder characterized by
constriction of the bronchioles, excessive mucus produc-
tion, and dyspnea; often caused by allergies (Chapter 15).
Astigmatism(uh-STIG-mah-TIZM) An error of refrac-
tion caused by an irregular curvature of the lens or
cornea (Chapter 9).
Astrocyte(ASS-troh-site) A type of neuroglia that forms
the blood–brain barrier to prevent potentially harmful
substances from affecting brain neurons (Chapter 8).
Asymptomatic(AY-simp-toh-MAT-ik) Without symptoms
(Chapter 22).
Atelectasis(AT-e-LEK-tah-sis) Collapsed or airless lung,
without gas exchange (Chapter 15).
Atherosclerosis(ATH-er-oh-skle-ROH-sis) The abnor-
mal accumulation of lipids and other materials in the
walls of arteries; narrows the lumen of the vessel and may
stimulate abnormal clot formation (Chapter 2).
Atlas(AT-las) An irregular bone, the first cervical vertebra;
supports the skull (Chapter 6).
Atmospheric pressure(AT-mus-FEER-ik) The pressure
exerted by the atmosphere on objects on the earth’s sur-
face; 760 mmHg at sea level (Chapter 15).
Atom(A-tom) The unit of matter that is the smallest part of
an element (Chapter 2).
Atomic number(a-TOM-ik) Number of protons in the
nucleus of an atom (Chapter 2).
Atomic weight(a-TOM-ik WAYT) The weight of an atom
determined by adding the number of protons and neu-
trons (Chapter 2).
ATP(Adenosine triphosphate) A specialized nucleotide
that traps and releases biologically useful energy
(Chapter 2).
Atrial natriuretic peptide(ANP) (AY-tree-uhl NAY-tree-
yu-RET-ik) A peptide hormone secreted by the atria of
the heart when blood pressure or blood volume in-
creases; increases loss of sodium ions and water by the
kidneys (Syn.—atrial natriuretic hormone) (Chapter 12).
Atrioventricular (AV) node (AY-tree-oh-ven-TRIK-yoo-lar NOHD) The second part of the cardiac conduc-
tion pathway, located in the lower interatrial septum
(Chapter 12).
Atrium(AY-tree-um) (Pl.—atria) One of the two upper
chambers of the heart that receive venous blood from the
lungs or the body (Chapter 12).
Atrophy(AT-ruh-fee) Decrease in size of a body part due to
lack of use; a wasting (Chapter 7).
Attenuated (uh-TEN-yoo-AY-ted) Weakened, or less
harmful; used to describe the microorganisms contained
in vaccines, which have been treated to reduce their path-
ogenicity (Chapter 14).
Auditory bones(AW-di-tor-ee) The malleus, incus, and
stapes in the middle ear (Chapter 6).
Auerbach’s plexus (OW-er-baks PLEK-sus) The auto-
nomic nerve plexus in the external muscle layer of the
organs of the alimentary tube; regulates the contractions
of the external muscle layer (Syn.—myenteric plexus)
(Chapter 16).
Auricle(AW-ri-kuhl) The portion of the outer ear external
to the skull; made of cartilage covered with skin (Syn.—
pinna) (Chapter 9).
Autoclave (AW-toh-clayve) A machine that uses steam
under pressure for sterilization (Chapter 22).
Autoimmune disease(AW-toh-im-YOONdi-ZEEZ) A
condition in which the immune system produces anti-
bodies to the person’s own tissue (Chapter 6).
Autonomic nervous system (AW-toh-NOM-ik NER-
vuhs) The portion of the peripheral nervous system that
consists of visceral motor neurons to smooth muscle, car-
diac muscle, and glands (Chapter 8).
Autosomes(AW-toh-sohms) Chromosomes other than the
sex chromosomes; for people there are 22 pairs of auto-
somes in each somatic cell (Chapter 21).
Axial skeleton(AK-see-uhl) The portion of the skeleton
that consists of the skull, vertebral column, and rib cage
(Chapter 6).
Axis(AK-sis) An irregular bone, the second cervical verte-
bra; forms a pivot joint with the atlas (Chapter 6).
Axon(AK-sahn) The cellular process of a neuron that car-
ries impulses away from the cell body (Chapter 4).
Axon terminal(AK-sahn TER-mi-nuhl) The end of the
axon of a motor neuron, part of the neuromuscular junc-
tion (Chapter 7).—B—
B cell(B SELL) A subgroup of lymphocytes, including
memory B cells and plasma cells, both of which are
involved in adaptive immune responses (Chapter 11).
Bacillus(buh-SILL-us) (Pl.—bacilli) A rod-shaped bac-
terium (Chapter 22).
Bacteremia (bak-tah-REE-mee-ah) The presence of
bacteria in the blood, which is normally sterile (Chap-
ter 22).30Scanlon(p3) Glossary 8/17/06 11:08 AM Page 551