Glossary 593
lipocytes (LIP-oh-sights) fat-storing cells
lithotripsy (LITH-oh-TRIP-see) the use of intense,
ultrasonic sound waves to break up a kidney stone into
pieces small enough to be passed from the body in the
urine
lobes the name for the four regions of the brain—frontal,
parietal, occipital, and temporal
long bones bones that are long in shape, such as the
major bones of the arms and legs
longitudinal arch arch of the foot running lengthwise
loop of Henle (HEN-lee) see nephron loop
loose connective tissue type of connective tissue that
has cells and an extracellular matrix containing fi bers
running through it
lower extremity bones of the hips, legs, and feet
low-risk HPVs type of HPV infection that can cause
warts, but are not known to cause cancer
lumbar region (LUM-bar) low back region of the spine
composed of 5 vertebrae
lumen (LOO-mehn) the hollow inside portion of a body
cavity or tube
lunule (LOO-nyool) the white, crescent-shaped region at
the base of the nail
luteal phase the phase of the menstrual cycle that begins
at ovulation and ends with the onset of menstruation
luteinizing hormone (LH) (LOO-tee-in-ighz-ing) a tropic
hormone produced by the anterior pituitary gland that
signals the egg’s release from the follicle, stimulates
the production of progesterone and small amounts of
estrogen in women, and stimulates the interstitial cells of
the testes to produce testosterone in men
lymph clear, transparent, sometimes faintly yellow fl uid
that is collected from tissues throughout the body and
fl ows in the lymphatic vessels
lymph nodes small, bean-shaped structures found along
the lymphatic vessels throughout the body
lymphatic capillaries the smallest lymphatic vessels that
collect lymph in organs and tissues
lymphatic nodules small, localized clusters of dense
tissue formed by lymphocytes and macrophages
lymphatic tissue loose, connective tissue that contains
many lymphocytes and is found in mucous membranes
and certain organs throughout the body
lymphatic trunks large lymphatic vessels that drain
lymph from different parts of the body
lymphatic valves tissue fl aps that act as one-way valves
inside the lymphatic vessels
lymphatic vessels vessels that carry lymph
lymphedema (LIMF-eh-DEE-ma) a buildup of
extracellular fl uid in the body because of disruption in
lymphatic drainage
lymphocytes (LIM-foh-sights) white blood cells that are
abundant in lymphatic tissue
lysosome (LIGH-soh-sohm) a compartment where
reactions involving potentially dangerous enzymes and
reactants can be conducted in isolation from the cytoplasm
lysozyme an enzyme contained in tears that attacks
bacteria
M
macronutrients substances such as carbohydrates,
proteins, and fats that the body requires in relatively large
quantities
macrophages (MAK-roh-fay-jehz) cells that phagocytize
(surround and destroy) foreign cells, such as bacteria
and viruses
macular degeneration (MAK-yoo-lar) a condition that
causes a progressive loss of central vision
major histocompatibility complex glycoproteins
(MHCs) family of proteins found on the surfaces of
lymphocytes and other cells; help the immune system
recognize foreign antigens and ignore “self” tissues
malignant term for tumors that are cancerous
malignant melanoma (MEHL-a-NOH-ma) cancer of the
melanocytes; the most serious form of skin cancer
malleus see hammer
mammary glands the milk-producing glands in the
female
mandible (MAN-di-buhl) jaw bone
manubrium (ma-NOO-bree-um) upper portion of the
sternum (breast bone)
mass the quantity of matter contained in an object
mast cells connective tissue cell with granules (particles)
that contain histamine, a compound which, when
released into surrounding fl uid, activates an infl ammatory
response
matrix term for a growth zone
maxillary bones (MAK-sil-lair-ee) two fused bones that
form the upper jaw, house the upper teeth, and connect
to all other bones of the face, with the exception of the
mandible
maxillary sinuses (MAK-sil-lair-ee) air cavities in the
body of the maxilla that communicate with the middle
meatus of the nose
mean arterial pressure the overall pressure within the
cardiovascular system, which determines blood fl ow to
various organs
mechanical breakdown the breakdown of food into
smaller pieces, thus increasing its surface area
mechanoreceptors (MEHK-a-noh-ree-SEHP-tors)
chemical receptor cells that detect muscle contraction
and force generation during exercise; they quickly
increase inspiration rates when exercise begins
medial rotation inward (medial) movement of a body
segment in the transverse plane
mediastinum (MEH-dee-as-TIGH-num) the area of the
thoracic cavity between the lungs; houses the heart,
great blood vessels, trachea, esophagus, thoracic duct,
thymus gland, and other structures
medulla deep or middle portion of an organ, for example
the deep part of a lymph node
medulla oblongata (meh-DOOL-a AHB-lawn-gah-tah)
the lower portion of the brain stem, which regulates heart
rate, blood pressure, and breathing, and controls several
refl exes
medullary cavity (MEHD-oo-LAIR-ee) central hollow in
the long bones
meiosis a type of cell division that produces eggs (in
females) or sperm (in males), daughter cells with half the
chromosome number of the parent cell
melanin a pigment that protects the body against the
harmful effects of ultraviolet ray damage from the sun
melanin granules particles of melanin that are pushed
into skin cells as more melanin is produced
melanocytes (MEHL-a-noh-sights) specialized cells in
the skin that produce melanin
melatonin hormone that is released by the pineal gland
when the body is exposed to darkness; high levels of
melatonin cause the body to feel drowsy or sleepy
membrane attack complex (MAC) a complex of
complement proteins that create a large, lethal hole in
the cell membrane