596 Introduction to Anatomy and Physiology
oligodendrocytes (AHL-i-goh-DEHN-droh-sights) glial
cells that wrap around nerve fi bers and produce a fatty
insulating material called myelin
oocyte (OH-uh-sight) egg cell
oogenesis (oh-ah-JEHN-eh-sis) the process by which
oocytes, or female gametes, are generated
oogonia (oh-uh-GOH-nee-a) diploid stem cells in females
that are similar to spermatogonia in males
opportunistic infection an infection that rarely or never
occurs in people with a healthy immune system but that
may occur in a person with a damaged immune system
such as from AIDS
opposition touching any of your four fi ngers to the
thumb; this movement enables grasping of objects
opsonins (AHP-soh-nins) proteins that make cells more
attractive to phagocytes
opsonization the process of making cells attractive to
phagocytes
optic chiasma (kigh-AZ-ma) the point at which the optic
nerves cross
optic disc the junction between the optic nerve and the
eye; the location of the blind spot
optic nerve transmitter of visual sensory signals to the
occipital lobe of the brain
optic tracts the continuation of the optic nerve fi bers
beyond the optic chiasma
oral cavity opening within the mouth
orbicularis oris (or-BIK-yoo-LAH-ris) a skeletal muscle
located in the lips
orbital cavities openings that hold the eyes
organ body part organized to perform a specifi c function
organ of Corti a spiral-shaped ridge of epithelium in the
cochlear duct lined with hair cells that serve as hearing
receptors
organ system two or more organs working together to
perform specifi c functions
origin muscle attachment to a relatively fi xed structure
oropharynx (OR-oh-FAIR-ingks) the middle section of
the pharynx
osmosis (ahz-MOH-sis) the movement of water
molecules from a region of low osmotic pressure to a
region of high osmotic pressure
osmotic diuresis (ahs-MAHT-ik) an increase in urine
production caused by high osmotic pressure of the
glomerular fi ltrate, which “pulls” more water into the
fi ltrate
osmotic pressure (ahs-MAHT-ik) a pressure created by
the presence of dissolved substances in water
osseous tissue (AHS-ee-us) bone tissue
ossicles (AHS-i-kuhls) the body’s three smallest bones—
the hammer, anvil, and stirrup; found in the middle ear
ossifi cation (AHS-i-fi -KAY-shun) process of bone
formation
osteoarthritis degenerative disease of articular cartilage,
characterized by pain, swelling, range-of-motion
restriction, and stiffness
osteoblasts (AHS-tee-oh-BLASTS) specialized bone
cells that build new bone tissue
osteoclasts (AHS-tee-oh-KLASTS) specialized bone
cells that resorb bone tissue
osteocytes mature bone cells
osteon a Haversian system
osteopenia (AHS-tee-oh-PEE-nee-a) reduced bone
mass without the presence of a fracture
osteoporosis (AHS-tee-oh-poh-ROH-sis) condition
in which bone mineralization and strength are so
abnormally low that regular, daily activities can result in
painful fractures
otitis media (oh-TIGHT-is) an infection of the middle ear
caused by bacteria or a virus
oval window a membrane-covered opening that
connects the middle ear to the inner ear
ovarian cycle the sequence of events associated with
maturation and release of an oocyte
ovaries the female sex glands
ovulation the release of an oocyte, or egg, from the
ovarian follicle
oxyhemoglobin (AHK-see-HEE-moh-GLOH-bin)
molecule that is created when oxygen combines with the
heme part of the hemoglobin molecule
oxytocin (AHK-see-TOH-sin) a hormone that stimulates
uterine contractions during labor and milk secretion
during breastfeeding
P
pacemaker an important internal control mechanism of
the heart; sinoatrial node
pain a sign of infl ammation
palate (PAL-at) the structure consisting of hard and soft
components that separates the oral and nasal cavities;
the roof of the mouth
palatine bones (PAL-a-tighn) bones that form the
posterior part of the hard palate, or roof of the mouth
palatine tonsils two masses of lymphatic tissue that lie
in the back of the mouth, on the left and right sides; the
largest and most commonly infected tonsils
palpitations sensation of rapid heartbeat
pancreas a long, thin gland located posterior to the
stomach. As an endocrine gland, the pancreas secretes
insulin and glucagon, which control blood glucose levels;
as an exocrine gland, the pancreas secretes digestive
enzymes
pancreatic amylase a substance that breaks down
starches into chains that are as short as two sugar
molecules
pancreatic lipase a substance that breaks down lipids
into their constituent fatty acids and monoglycerides
pancreatitis (PAN-kree-a-TIGH-tis) infl ammation of the
pancreas
papilla the rounded tip of a renal pyramid, through which
collecting tubules discharge urine
papillae (pa-PIL-ee) bumps on the surface of the tongue,
some of which house taste buds
papillary layer (PAP-i-LAIR-ee) the outer layer of the
dermis
papillary muscle (PAP-i-LAIR-ee) one of the small
muscular bundles attached at one end to the
chordae tendineae and at the other to the innermost or
endocardial wall of the ventricles; maintains tension on
the chordae tendineae as the ventricle contracts
parallel a type of muscle fi ber arrangement in which
fi bers run largely parallel to each other along the length
of the muscle
paraplegia (PAIR-ah-PLEE-jee-a) disorder characterized
by loss of function in the lower trunk and legs
parathyroid glands two pairs of glands located on
the posterior aspect of the thyroid gland that secrete
parathyroid hormone in response to low blood calcium
levels
parathyroid hormone (PTH) hormone produced by the
parathyroid glands that works with calcitonin to maintain
calcium homeostasis