Sympathomimetic (sim'-pa-thO-mi-MET-ik) Producing effects that
mimic those brought about by the sympathetic division of the
autonomic nervous system.
Symphysis (SIM-fi-sis) A line of union. A slightly movable fibrocarti-
laginous joint such as the pubic symphysis.
Symptom (SIMP-tum) A subjective change in body function not
apparent to an observer, such as pain or nausea, that indicates
the presence of a disease or disorder of the body.
Synapse (SYN-aps) The functional junction between two neurons
or between a neuron and an effector, such as a muscle or gland;
may be electrical or chemical.
Synaptic cleft (sin-AP-tik) The narrow gap at a chemical synapse that
separates the axon terminal of one neuron from another neuron
or muscle fiber (cell) and across which a neurotransmitter diffuses
to affect the postsynaptic cell.
Synaptic end bulb Expanded distal end of an axon terminal that
contains synaptic vesicles. Also called a synaptic knob.
Synaptic vesicle Membrane-enclosed sac in a synaptic end bulb that
Synarthrosis (sin'-ar-THRO-sis) An immovable or slightly movable
joint such as a suture, gomphosis, and synchondrosis.
Synchondrosis (sin'-kon-DRO-sis) A cartilaginous joint in which the
connecting material is hyaline cartilage.
Syndesmosis (sin'-dez-MO-sis) A slightly movable joint in which
articulating bones are united by fibrous connective tissue.
Syndrome (SIN-drom) A group of signs and symptoms that occur
together in a pattern that is characteristic of a particular disease
or abnormal condition.
Synergist (SIN-er-jist) A muscle that assists the prime mover by
reducing undesired action or unnecessary movement.
Synostosis (sin'-os-TO-sis) A joint in which the dense fibrous con-
nective tissue that unites bones at a suture has been replaced by
bone, resulting in a complete fusion across the suture line.
Synovial cavity (si-NO-ve-al) The space between the articulating bones
of a synovial joint, filled with synovial fluid. Also called a joint cavity.
Synovial fluid Secretion of synovial membranes that lubricates joints
and nourishes articular cartilage.
Synovial joint A fully movable or diarthrotic joint in which a synovial
(joint) cavity is present between the two articulating bones.
Synovial membrane The deeper of the two layers of the articular
capsule of a synovial joint, composed of areolar connective tissue
that secretes synovial fluid into the synovial (joint) cavity.
System An association of organs that have a common function.
Systemic (sis-TEM-ik) Affecting the whole body; generalized.
Systemic anatomy The anatomic study of particular systems of the
body, such as the skeletal, muscular, nervous, cardiovascular, or
Systemic circulation The routes through which oxygenated blood
flows from the left ventricle through the aorta to all the organs
of the body except the lungs and deoxygenated blood returns to
the right atrium.
Systemic vascular resistance (SVR) All the vascular resistance offered
by systemic blood vessels. Also called total peripheral resistance.
Systole (SIS-to-le) In the cardiac cycle, the phase of contraction of
the heart muscle, especially of the ventricles.
Systolic blood pressure (sis-TOL-ik) The force exerted by blood on
arterial walls during ventricular contraction; the highest pressure
measured in the large arteries, about 110 mmHg under normal
conditions for a young adult.
T cell A lymphocyte that becomes immunocompetent in the thymus
and can differentiate into a helper T cell or a cytotoxic T cell, both
of which function in cell-mediated immunity.
T wave The deflection wave of an electrocardiogram that represents
Tachycardia (tak'-i-KAR-de-a) An abnormally rapid resting heartbeat
or pulse rate (over 100 beats per minute).
Tactile (TAK-tTl) Pertaining to the sense of touch.
Target cell A cell whose activity is affected by a particular hormone.
Tarsal bones The seven bones of the ankle. Also called tarsals.
Tarsal gland Sebaceous (oil) gland that opens on the edge of each
eyelid. Also called a Meibomian gland (mT-BO-me-an).
Tarsal plate A thin, elongated sheet of connective tissue, one in each
eyelid, giving the eyelid form and support. The aponeurosis of the
levator palpebrae superioris is attached to the tarsal plate of the
Tarsus (TAR-sus) A collective term for the seven bones of the ankle.
Tectorial membrane (tek-TO-re-al) A gelatinous membrane projecting
over and in contact with the hair cells of the spiral organ (organ of
Corti) in the cochlear duct.
Teeth (TE-TH) Accessory structures of digestion, composed of
calcified connective tissue and embedded in bony sockets of the
mandible and maxilla, that cut, shred, crush, and grind food. Also
called dentes (DEN-tez).
Telophase (TEL-o-faz) The final stage of mitosis in which two nuclei
Tendon (TEN-don) A white fibrous cord of dense regular connective
tissue that attaches muscle to bone.
Tendon organ A proprioceptive receptor, sensitive to changes in muscle
tension and force of contraction, found chiefly near the junctions of
tendons and muscles. Also called a Golgi tendon organ (GOL-je).
Tendon reflex A polysynaptic, ipsilateral reflex that protects tendons
and their associated muscles from damage that might be brought
about by excessive tension. The receptors involved are called
tendon organs (Golgi tendon organs).
Teratogen (TER-a-to-jen) Any agent or factor that causes physical
defects in a developing embryo.
Testis (TES-tis) Male gonad that produces sperm and the hormones
testosterone and inhibin. Also called a testicle.
Testosterone (tes-TOS-te-ron) A male sex hormone (androgen)
secreted by interstitial endocrinocytes (Leydig cells) of a mature
testis; needed for development of sperm; together with a second
androgen termed dihydrotestosterone (DHT), controls the growth
and development of male reproductive organs, secondary sex
characteristics, and body growth.