Glossary 583permanent loss of spinal cord reflexes following injury to
the spinal cord (Chapter 8).
Spirillum (spih-RILL-uhm) (Pl.—spirilla) A bacterium
with a spiral shape (Chapter 22).
Spirochete (SPY-roh-keet) Spiral bacteria of the order
Spirochaetales (Chapter 22).
Spleen(SPLEEN) An organ located in the upper left
abdominal quadrant behind the stomach; consists of lym-
phatic tissue that produces lymphocytes; also contains
macrophages that phagocytize old red blood cells
(Chapter 14).
Spongy bone(SPUN-jee BOWNE) Bone tissue not organ-
ized into haversian systems; forms most of the short, flat,
and irregular bones and forms epiphyses of long bones
(Chapter 6).
Spontaneous fracture(spahn-TAY-nee-us) A fracture that
occurs without apparent trauma; often a consequence of
osteoporosis (Syn.—pathologic fracture) (Chapter 6).
Spore(SPOOR) 1. A bacterial form that is dormant and
highly resistant to environmental extremes such as heat.- A unicellular fungal reproductive form (Chapter 22).
Squamous(SKWAY-mus) Flat or scale-like; used especially
in reference to epithelial tissue (Chapter 4).
Stapes(STAY-peez) The third of the auditory bones in the
middle ear; transmits vibrations from the incus to the
oval window of the inner ear (Chapter 9).
Starch(STARCH) A polysaccharide produced by plants;
digested to glucose, a source of energy for cell respiration
(Chapter 2).
Starling’s law of the heart(STAR-lingz LAW) The force
of contraction of cardiac muscle fibers is determined by
the length of the fibers; the more cardiac muscle fibers
are stretched, the more forcefully they contract (Chap-
ter 12).
Stem cell(STEM SELL) 1. An embryonic cell capable of
differentiating into any of the specialized cells of an
organism (Chapter 3). 2. The unspecialized cell found in
red bone marrow and lymphatic tissue that is the precur-
sor cell for all types of blood cells (Chapter 11). 3. Any
unspecialized cell with the potential to differentiate
(Chapter 3).
Stenosis(ste-NOH-sis) An abnormal constriction or nar-
rowing of an opening or duct (Chapter 12).
Sterilization(STIR-ill-i-ZAY-shun) The process of com-
pletely destroying all of the microorganisms on or in a
substance or object (Chapter 22).
Sternum(STIR-num) The flat bone that forms part of the
anterior rib cage; consists of the manubrium, body, and
xiphoid process (Syn.—breastbone) (Chapter 6).
Steroid(STEER-oyd) An organic compound in the lipid
group; includes cholesterol and the sex hormones
(Chapter 2).
Stimulus(STIM-yoo-lus) A change, especially one that
affects a sensory receptor or that brings about a response
in a living organism (Chapter 9).
Stomach(STUM-uk) The sac-like organ of the alimentary
tube between the esophagus and the small intestine; is a
reservoir for food and secretes gastric juice to begin pro-
tein digestion (Chapter 16).
Strabismus(strah-BIZ-mis) An impairment of binocular
vision, the optic axes of the eyes cannot be oriented prop-
erly on an object because of an imbalance in one set of
extrinsic muscles; the “lazy eye” may drift medially or lat-
erally (Chapter 9).
Stratified(STRA-ti-fyed) Having two or more layers
(Chapter 4).
Stratum corneum(STRA-tum KOR-nee-um) The outer-
most layer of the epidermis, made of many layers of dead,
keratinized cells (Chapter 5).
Stratum germinativum (STRA-tum JER-min-ah-TEE-
vum) The innermost layer of the epidermis; the cells
undergo mitosis to produce new epidermis (Syn.—stra-
tum basale) (Chapter 5).
Streptokinase(STREP-toh-KYE-nase) An enzyme pro-
duced by bacteria of the genus Streptococcusthat was used
clinically to dissolve abnormal clots, such as those in
coronary arteries (Chapter 11).
Stretch receptor (STRETCH ree-SEP-ter) A sensory
receptor in a muscle that detects stretching of the muscle
(Syn.—proprioceptor) (Chapter 7).
Stretch reflex(STRETCH REE-fleks) A spinal cord reflex
in which a muscle that is stretched will contract (Chap-
ter 8).
Striated muscle(STRY-ay-ted MUSS-uhl) The muscle
tissue that forms the skeletal muscles that move bones
(Syn.—voluntary, skeletal muscle) (Chapter 4).
Stroke volume(STROHK VAHL-yoom) The amount of
blood pumped by a ventricle in one beat; the resting
average is 60–80 mL/beat (Chapter 12).
Subarachnoid space (SUB-uh-RAK-noid) The space
between the arachnoid membrane and the pia mater;
contains cerebrospinal fluid (Chapter 8).
Subclinical infection(sub-KLIN-i-kuhl) An infection in
which the person shows no symptoms (Syn.—inapparent,
asymptomatic) (Chapter 22).
Subcutaneous(SUB-kew-TAY-nee-us) Below the skin; the
superficial fascia between the dermis and the muscles
(Chapter 5).
Sublingual glands(sub-LING-gwal) The pair of salivary
glands located below the floor of the mouth (Chap-
ter 16).
Submandibular glands(SUB-man-DIB-yoo-lar) The pair
of salivary glands located at the posterior corners of the
mandible (Chapter 16).
Submucosa(SUB-mew-KOH-sah) The layer of connective
tissue and blood vessels located below the mucosa (lin-
ing) of a mucous membrane (Chapter 16).
Substrates(SUB-strayts) The substances acted upon, as by
enzymes (Chapter 2).
Sucrase(SOO-krays) A digestive enzyme that breaks down30Scanlon(p3) Glossary 8/17/06 11:08 AM Page 583