Static equilibrium (e-kwi-LIB-re-um) The maintenance of posture in
response to changes in the orientation of the body, mainly the
head, relative to the ground.
Stellate reticuloendothelial cell (STEL-at re-tik'-u-lo-en'-do-THE-le-al)
Phagocytic cell within a sinusoid of the liver. Also called a Kupffer
Stem cell Unspecialized cell that has the ability to divide for indefi-
nite periods and give rise to specialized cells.
Stenosis (sten-O-sis) An abnormal narrowing or constriction of a
duct or opening.
Sterile (STE-ril) Free from any living microorganisms. Unable to con-
ceive or produce offspring.
Sterilization (ster'-i-li-ZA-shun) Elimination of all living microorgan-
isms. Any procedure that renders an individual incapable of
reproduction (for example, castration, vasectomy, hysterectomy,
Stimulus Any stress that changes a controlled condition; any change
in the internal or external environment that excites a sensory
receptor, a neuron, or a muscle fiber.
Stomach The J-shaped enlargement of the gastrointestinal tract
directly inferior to the diaphragm in the epigastric, umbilical, and
left hypochondriac regions of the abdomen, between the esopha-
gus and small intestine.
Stratum (STRA-tum) A layer.
Stressor A stress that is extreme, unusual, or long-lasting and trig-
gers the stress response.
Stress response Wide-ranging set of bodily changes, triggered by a
stressor, that gears the body to meet an emergency. Also known
as general adaptation syndrome (GAS).
Stretch receptor Receptor in the walls of blood vessels, airways, or
organs that monitors the amount of stretching. Also termed a
Stretch reflex A monosynaptic reflex triggered by sudden stretching
of muscle spindles within a muscle that elicits contraction of that
same muscle. Also called a tendon jerk.
Stroke volume The volume of blood ejected by either ventricle dur-
ing one systole; about 70 mL in an adult at rest.
Subarachnoid space (sub'-a-RAK-noyd) A space between the
arachnoid mater and the pia mater that surrounds the brain
and spinal cord and through which cerebrospinal fluid
Subcutaneous (sub'-ku-TA-ne-us) Beneath the skin. Also called hypo-
Subcutaneous layer A continuous sheet of areolar connective tissue
and adipose tissue between the dermis of the skin and the deep
fascia of the muscles.
Subdural space (sub-DOO-ral) A space between the dura mater and
the arachnoid mater of the brain and spinal cord that contains a
small amount of fluid.
Sublingual gland (sub-LING-gwal) One of a pair of salivary glands
situated in the floor of the mouth deep to the mucous membrane
and to the side of the lingual frenulum, with a duct that opens
into the floor of the mouth.
Submandibular gland (sub'-man-DIB-u-lar) One of a pair of salivary
glands found inferior to the base of the tongue deep to the mucous
membrane in the posterior part of the floor of the mouth, posterior
to the sublingual glands, with a duct situated to the side of the lin-
gual frenulum. Also called the submaxillary gland (sub'-MAK-si-ler-e).
Submucosa (sub-mu-KO-sa) A layer of connective tissue located
deep to a mucous membrane, as in the gastrointestinal tract or
the urinary bladder; the submucosa connects the mucosa to the
Substrate A molecule upon which an enzyme acts.
Sudoriferous gland (soo'-dor-IF-er-us) An apo crine or eccrine exo-
crine gland in the dermis or subcutaneous layer that produces
perspiration. Also called a sweat gland.
Sulcus (SUL-kus) A groove or depression between parts, especially
between the convolutions of the brain.
P lu r a l
is sulci (SUL-sT).
Summation (sum-MA-shun) The addition of the excitatory and inhibi-
tory effects of many stimuli applied to a neuron. The increased
strength of muscle contraction that results when stimuli follow
one another in rapid succession.
Superficial (soo'-per-FISH-al) Located on or near the surface of the
body or an organ.
Superior (soo-PER-e-or) Toward the head or upper part of a structure.
Superior vena cava (SVC) (VE-na CA-va) Large vein that collects blood
from parts of the body superior to the heart and returns it to the
Supination (soo-pi-NA-shun) A movement of the forearm in which
the palm is turned anteriorly.
Surface anatomy The study of the structures that can be identified
from the outside of the body.
Surfactant (sur-FAK-tant) Complex mixture of phospholipids and lipo-
proteins, produced by type II alveolar (septal) cells in the lungs,
that decreases surface tension.
Susceptibility (sus-sep'-ti-BIL-i-te) Lack of resistance to the damaging
effects of an agent such as a pathogen.
Suspensory ligament (sus-PEN-so-re LIG-a-ment) A fold of perito-
neum extending laterally from the surface of the ovary to the
Sutural bone (SOO-cher-al) A small bone located within a suture
between certain cranial bones.
Suture (SOO-cher) An immovable or slightly movable fibrous joint
that joins skull bones.
Sympathetic division (sim'-pa-THET-ik) One of the two subdivisions of
the autonomic nervous system, having cell bodies of preganglionic
neurons in the lateral gray columns of the thoracic segment and
the first two or three lumbar segments of the spinal cord; primarily
concerned with processes involving the expenditure of energy.
Sympathetic trunk ganglion (GANG-gle-on) A cluster of cell bodies
of sympathetic postganglionic neurons lateral to the vertebral
column, close to the body of a vertebra. These ganglia extend
inferiorly through the neck, thorax, and abdomen to the coccyx
on both sides of the vertebral column and are connected to one
another to form a chain on each side of the vertebral column.
Also called sympathetic chain or vertebral chain ganglia.