Glossary 581
apocrine glands (AP-oh-krin) glands that secrete a milky
fl uid consisting of sweat, fatty acids, and proteins
aponeurosis (AP-oh-noo-ROH-sis) a fl at, sheetlike
fi brous tissue that connects muscle or bone to other
tissues
apophysis (a-PAHF-i-sis) site at which a tendon attaches
to bone
apoptosis (AP-ahp-TOH-sis) a programmed process of
cellular self-destruction (cell suicide)
appendicular skeleton the bones of the body’s
appendages; the arms and legs
appendix a small, closed-end extension of the large
intestine near the junction of the large and small
intestines
aquaporin (ah-kwah-POR-in) a protein in the cell
membrane that acts as a channel for water to enter or
exit the cell
aqueous and vitreous humors (AY-kwee-us and
VIT-ree-us) the watery fl uid that fi lls the anterior and
posterior chambers of the eye
arachnoid mater the middle membrane of the brain,
which is composed of web-like tissue
areola (a-REE-oh-la) a circular area of pigmented skin
that surrounds the protruding nipple
areolar connective tissue a type of tissue that is found
throughout the body, typically as a layer under epithelial
tissues
arrector pili (ah-REHK-tor PIGH-ligh) tiny muscles that
connect either side of a hair follicle to the epidermis
arrhythmia (ay-RITH-mee-a) an irregular heartbeat or
rhythm
arteries vessels that carry blood away from the heart
arterioles (ar-TAIR-ee-ohls) microscopic arteries that
connect with capillaries
arthritis family of more than 100 common pathologies
associated with aging, characterized by joint
infl ammation accompanied by pain, stiffness, and
sometimes swelling
articular cartilage (ar-TIK-yoo-lar) dense, white,
connective tissue that covers the articulating surfaces of
bones at joints
articular fi brocartilage (ar-TIK-yoo-lar FIGH-broh-KAR-
ti-lij) tissue shaped like a disc or partial disc called a
meniscus that provides cushioning at a joint
ascending colon the segment of the colon that extends
upward from the cecum to the bend on the right side
below the liver
ascending limb the fi nal part of the nephron loop
through which fi ltrate fl ows; is made mostly or entirely of
a thick-walled segment
asexual reproduction reproduction that involves only
one cell rather than the fusion of two gametes
association cortex the most anterior portion of the
frontal lobe, which is believed to be responsible for
intellect
asthma (AZ-ma) disease of the lungs characterized
by recurring episodes of airway infl ammation causing
bronchospasms and increased mucus production
astigmatism (a-STIG-ma-tizm) a common eye disorder
caused by an irregular curvature of the cornea or lens
that results in blurred vision
astrocytes (AS-troh-sights) glial cells that are positioned
between neurons and capillaries to transmit nutrients and
control the chemical environment
atherosclerosis (ATH-er-oh-skler-OH-sis) hardening of
the arteries
atlas the fi rst cervical vertebra; specialized to provide the
connection between the occipital bone of the skull and
the spinal column
atoms tiny particles of matter
ATP (a-DEHN-oh-seen trigh-FAHS-fayt) a nucleotide
composed of an adenine base, a sugar, and three
phosphate groups; adenosine triphosphate
ATP synthase an enzyme present in large numbers in
the inner cell membrane which makes ATP
atrial fi brillation condition in which the atria contract in
an uncoordinated, rapid manner (rate above 350 bpm),
causing the ventricles to contract irregularly
atrial natriuretic peptide (ANP) (NA-tree-yoo-REHT-ik)
a peptide hormone secreted by the atria of the heart
that promotes excretion of sodium and water and lowers
blood pressure
atrioventricular node (AV node) (AY-tree-oh-vehn-TRIK-
yoo-lar) a small mass of tissue that transmits impulses
received from the sinoatrial node to the ventricles via the
bundle of His
atrioventricular (AV) valves the two valves (tricuspid
and mitral) situated between the atria and the ventricles
atrophy decrease in bone mineral density and strength
auditory canal a short, tubelike structure that connects
the outer ear to the eardrum
auricle (AW-ri-kuhl) the irregularly shaped outer portion
of the ear
auscultation (AWS-kul-TAY-shun) the act of listening to
internal sounds of the body using a stethoscope
autoimmune disorder a condition in which the immune
system attacks the body’s own tissue
autonomic nervous system branch of the nervous
system that controls involuntary body functions
autonomic refl exes involuntary stimuli transmitted to
cardiac and smooth muscle
axial skeleton central, stable portion of the skeletal
system, consisting of the skull, spinal column, and
thoracic cage
axis the second cervical vertebra; specialized with an
upward projection called the odontoid process, on which
the atlas rotates
axon a long, thin fi ber connected to the motor neuron cell
body
axon terminals offshoots of the axon that branch out to
connect with individual muscle fi bers
B
B cells see B lymphocytes
B lymphocytes lymphocytes that mature in the bone
marrow before moving out to the blood and the rest of
the body; B cells
ball-and-socket joint synovial joint formed between one
bone end shaped roughly like a ball and the receiving
bone reciprocally shaped like a socket
balloon angioplasty a surgical procedure to open the
blocked vessel resulting from a heart attack
baroreceptors (BAIR-oh-ree-SEP-ters) pressure sensitive
nerve endings in the atrium, aortic arch, and carotid arteries
basal toward the base; when used to describe an
epithelium, it refers to the surface that faces the inside of
the body
basal cell carcinoma (KAR-si-NOH-ma) the most
common form of skin cancer and the least malignant type
basal metabolic rate the amount of energy required to
sustain a person’s metabolism for one day if he or she is
at complete rest; BMR