574 GlossaryOligodendrocyte(ah-li-goh-DEN-droh-sight) A type of
neuroglia that produces the myelin sheath around neu-
rons of the central nervous system (Chapter 8).
Oligosaccharide(ah-lig-oh-SAK-ah-ride) A carbohydrate
molecule that consists of from 3–20 monosaccharides
bonded together; form “self ” antigens on cell mem-
branes (Chapter 2).
Oliguria(AH-li-GYOO-ree-ah) Decreased urine forma-
tion and output (Chapter 18).
Oogenesis(Oh-oh-JEN-e-sis) The process of meiosis in
the ovary to produce an ovum (Chapter 3).
Opportunistic infection(OP-er-too-NIS-tik) An infection
caused by a microorganism that is usually a saprophyte
but may become a parasite under certain conditions, such
as lowered host resistance (Chapter 22).
Opsonization (OP-sah-ni-ZAY-shun) The action of
antibodies or complement that upon binding to a for-
eign antigen attracts macrophages and facilitates phago-
cytosis (from the Greek “to purchase food”) (Chap-
ter 14).
Optic chiasma(OP-tik kye-AS-muh) The site of the cross-
ing of the medial fibers of each optic nerve, anterior to
the pituitary gland; important for binocular vision
(Chapter 9).
Optic disc(OP-tik DISK) The portion of the retina where
the optic nerve passes through; no rods or cones are pres-
ent (Syn.—blind spot) (Chapter 9).
Optic nerves(OP-tik) Cranial nerve pair II; sensory for
vision (Chapter 8).
Oral cavity(OR-uhl KAV-i-tee) The cavity in the skull
bounded by the hard palate, cheeks, and tongue (Chapter
16).
Orbit(OR-bit) The cavity in the skull that contains the
eyeball (Syn.—eye socket) (from the Latin “circle” or
“world”) (Chapter 9).
Orbitofrontal cortex(OR-bih-toh-FRUN-tuhl) The part
of the frontal lobe behind the eye; is concerned with
appropriate emotions and behavior, and awareness of the
future (Syn.—prefrontal cortex) (Chapter 8).
Organ(OR-gan) A structure with specific functions; made
of two or more tissues (Chapter 1).
Organ of Corti(KOR-tee) (spiral organ) The structure in
the cochlea of the inner ear that contains the receptors
for hearing (Chapter 9).
Organ system(OR-gan SIS-tem) A group of related organs
that work together to perform specific functions (Chap-
ter 1).
Organelle(OR-gan-ELL) An intracellular structure that
has a specific function (Chapter 3).
Organic(or-GAN-ik) A chemical compound that contains
carbon–hydrogen covalent bonds; includes carbohy-
drates, lipids, proteins, and nucleic acids (Chapter 1).
Origin (AHR-i-jin) 1. The more stationary attachment
point of a muscle to a bone. 2. The beginning (Chap-
ter 7).Oropharynx(OR-oh-FA-rinks) The middle portion of the
pharynx behind the oral cavity; a passageway for both air
and food (Chapter 15).
Osmolarity (ahs-moh-LAR-i-tee) The concentration of
osmotically active particles in a solution (Chapter 19).
Osmoreceptors(AHS-moh-re-SEP-ters) Specialized cells
in the hypothalamus that detect changes in the water
content of the body (Chapter 10).
Osmosis(ahs-MOH-sis) The diffusion of water through a
selectively permeable membrane (Chapter 3).
Osmotic pressure(ahs-MAH-tik) Pressure that develops
when two solutions of different concentration are sepa-
rated by a selectively permeable membrane. A hypertonic
solution that would cause cells to shrivel has a higher
osmotic pressure. A hypotonic solution that would cause
cells to swell has a lower osmotic pressure (Chapter 3).
Ossification(AHS-i-fi-KAY-shun) The process of bone
formation; bone matrix is produced by osteoblasts during
the growth or repair of bones (Chapter 6).
Osteoarthritis(AHS-tee-oh-ar-THRY-tiss) The inflam-
mation of a joint, especially a weight-bearing joint, that
is most often a consequence of aging (Chapter 6).
Osteoblast(AHS-tee-oh-BLAST) A bone-producing cell;
produces bone matrix for the growth or repair of bones
(Chapter 6).
Osteoclast(AHS-tee-oh-KLAST) A bone-destroying cell;
reabsorbs bone matrix as part of the growth or repair of
bones (Chapter 6).
Osteocyte(AHS-tee-oh-sight) A bone cell (Chapter 4).
Osteomyelitis (AHS-tee-oh-my-uh-LY E-tiss) Inflamma-
tion of a bone caused by a pathogenic microorganism
(Chapter 6).
Osteon(AHS-tee-on) The structural unit of compact bone,
consisting of a central (haversian) canal surrounded by
concentric rings of osteocytes within matrix (Syn.—
haversian system) (Chapter 4).
Osteoporosis (AHS-tee-oh-por-OH-sis) A condition in
which bone matrix is lost and not replaced, resulting in
weakened bones that are then more likely to fracture
(Chapter 6).
Otitis media(oh-TIGH-tis MEE-dee-ah) Inflammation of
the middle ear (Chapter 9).
Otoliths(OH-toh-liths) Microscopic crystals of calcium
carbonate in the utricle and saccule of the inner ear; are
pulled by gravity (Chapter 9).
Oval window(OH-vul WIN-doh) The membrane-covered
opening through which the stapes transmits vibrations to
the fluid in the inner ear (Chapter 9).
Ovary(OH-vuh-ree) The female gonad that produces ova;
also an endocrine gland that produces the hormones
estrogen and progesterone (Chapter 10).
Ovum(OH-vuhm) (Pl.—ova) An egg cell, produced by an
ovary (Chapter 20).
Oxygen debt(AHKS-ah-jen DET) The state in which
there is not enough oxygen to complete the process of30Scanlon(p3) Glossary 8/17/06 11:08 AM Page 574