Glossary
G-21
Substrate
A reactant on which an enzyme acts to cause a chemical action
to proceed.
Sudoriferous gland
(su
0
do-rif
9
er-us) Epidermal gland that produces
sweat.
Sulcus
(sul
9
kus) A furrow on the brain, less deep than a fissure.
Summation
Accumulation of effects, especially those of muscular, sen-
sory, or mental stimuli.
Superficial
Located close to or on the body surface.
Superior
Toward the head or upper body regions.
Superior vena cava
Vein that returns blood from body regions superior
to the diaphragm.
Supination
(soo
0
pĭ-na
9
shun) ±e outward rotation of the forearm caus-
ing palms to face anteriorly.
Surfactant
(ser-fak
9
tant) Secretion produced by certain cells of the al-
veoli that reduces the surface tension of water molecules, thus preventing
the collapse of the alveoli aFer each expiration.
Suspension
Heterogeneous mixtures with large, oFen visible solutes that
tend to settle out.
Suture
(soo
9
cher) An immovable fibrous joint; with one exception, all
bones of the skull are united by sutures.
Sweat gland
See
Sudoriferous gland.
Sympathetic division
±e division of the autonomic nervous system
that prepares the body for activity or to cope with some stressor (danger,
excitement, etc.); the fight, fright, and flight subdivision.
Sympathetic (vasomotor) tone
State of partial vasoconstriction of the
blood vessels maintained by sympathetic fibers.
Symphysis
(sim
9
fih-sis) A joint in which the bones are connected by
fibrocartilage.
Synapse
(sin
9
aps) ²unctional junction or point of close contact between
two neurons or between a neuron and an effector cell.
Synapsis
(sĭ-nap
9
sis) Pairing of homologous chromosomes during the
first meiotic division.
Synaptic cleF
(sĭ-nap
9
tik) ²luid-filled space at a synapse.
Synaptic delay
Time required for a signal to cross a synapse between
two neurons.
Synaptic vesicles
Small membranous sacs containing neurotransmitter.
Synarthrosis
(sin
0
ar-thro
9
sis) Immovable joint.
Synchondrosis
(sin
0
kon-dro
9
sis) A joint in which the bones are united
by hyaline cartilage.
Syndesmosis
(sin
0
des-mo
9
sis) A joint in which the bones are united by a
ligament or a sheet of fibrous tissue.
Synergist
(sin
9
er-jist) (1) Muscle that aids the action of a prime mover
by effecting the same movement or by stabilizing joints across which the
prime mover acts, preventing undesirable movements. (2) Hormone that
amplifies the effect of another hormone at a target cell.
Synostosis
(sin
0
os-to
9
sis) A completely ossified joint; a fused joint.
Synovial fluid
²luid secreted by the synovial membrane; lubricates joint
surfaces and nourishes articular cartilages.
Synovial joint
²reely movable joint exhibiting a joint cavity; also called
a diarthrosis.
Synthesis (combination) reaction
A chemical reaction in which larger,
more complex atoms or molecules are formed from simpler ones.
Systemic
(sis-tem
9
ik) Pertaining to the whole body.
Systemic circuit
System of blood vessels that serves gas exchange in the
body tissues.
Solute
(sol
9
yoot) ±e substance that is dissolved in a solution.
Solute pump
Enzyme-like protein carrier that mediates active transport
of solutes such as amino acids and ions uphill against their concentration
gradients.
Somatic nervous system
(so-mă
9
tik) Division of the peripheral nervous
system that provides the motor innervation of skeletal muscles; also
called the voluntary nervous system.
Somatic reflexes
Reflexes that activate skeletal muscle.
Somatosensory system
±at part of the sensory system dealing with
reception in the body wall and limbs; receives inputs from exteroceptors,
proprioceptors, and interoceptors.
Somite
(so
9
mīt) A mesodermal segment of the body of an embryo that
contributes to the formation of skeletal muscles, vertebrae, and dermis of
skin.
Spatial discrimination
±e ability of neurons to identify the site or pat-
tern of stimulation.
Special senses
±e senses of taste, smell, vision, hearing, and equilib-
rium.
Specific gravity
Term used to compare the weight of a substance to the
weight of an equal volume of distilled water.
Sperm (spermatozoon)
Male gamete.
Spermatogenesis
(sper
0
mah-to-jen
9
ĕ-sis) ±e process of sperm (male
gamete) formation; involves meiosis.
Sphincter
(sfink
9
ter) A circular muscle surrounding an opening; acts as
a valve.
Spinal cord
±e bundle of nervous tissue that runs from the brain to the
first to third lumbar vertebrae and provides a conduction pathway to and
from the brain.
Spinal nerves
±e 31 nerve pairs that arise from the spinal cord.
Splanchnic circulation
(splangk
9
nik) ±e blood vessels serving the di-
gestive system.
Spleen
Largest lymphoid organ; provides for lymphocyte proliferation,
immune surveillance and response, and blood-cleansing functions.
Spongy bone
Internal layer of skeletal bone. Also called cancellous bone.
Sprain
Ligaments reinforcing a joint are stretched or torn.
Static equilibrium
Sense of head position in space with respect to gravity.
Stenosis
(stĕ-no
9
sis) Abnormal constriction or narrowing.
Steroids
(stĕ
9
roidz) Group of chemical substances including certain hor-
mones and cholesterol; they are fat soluble and contain little oxygen.
Stimulus
(stim
9
u-lus) An excitant or irritant; a change in the environ-
ment that evokes a response.
Stomach
Temporary reservoir in the gastrointestinal tract where chemi-
cal breakdown of proteins begins and food is converted into chyme.
Stressor
Any stimulus that directly or indirectly causes the hypothalamus to
initiate stress-reducing responses, such as the fight-or-flight response.
Stroke
See
Cerebrovascular accident.
Stroke volume (SV)
Amount of blood pumped out of a ventricle during
one contraction.
Stroma
(stro
9
mah) ±e basic internal structural framework of an organ.
Structural (fibrous) proteins
Consist of extended, strandlike polypep-
tide chains forming a strong, ropelike structure that is linear, insoluble in
water, and very stable; e.g., collagen.
Subcutaneous
(sub
0
kyu-ta
9
ne-us) Beneath the skin.
Subendocardial conducting network
Modified ventricular muscle fi-
bers of the conduction system of the heart. Also called Purkinje fibers.
previous page 1197 Human Anatomy and Physiology (9th ed ) 2012 read online next page 1199 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off