Glossary
G-13
Latent period
Period of time between stimulation and the onset of
muscle contraction.
Lateral
Away from the midline of the body.
Leptin
Hormone released by fat cells that signals satiety.
Leukemia
Refers to a group of cancerous conditions of white blood cells.
Leukocytes
(loo
9
ko-sīts) White blood cells; formed elements involved in
body protection that take part in inflammatory and immune responses.
Leukocytosis
An increase in the number of leukocytes (white blood
cells); usually the result of a microbiological attack on the body.
Leukopenia
(loo
0
ko-pe
9
ne-ah) Abnormally low white blood cell count.
Leukopoiesis
Te production of white blood cells.
Lever system
Consists of a lever (bone), effort (muscle action), resistance
(weight of object to be moved), and fulcrum (joint).
Ligament
(lig
9
ah-ment) Band of regular fibrous tissue that connects bones.
Ligands
Signaling chemicals that bind specifically to membrane receptors.
Limbic system
(lim
9
bik) Functional brain system involved in emotional
response and memory formation.
Lipid
(lih
9
pid) Organic compound formed of carbon, hydrogen, and
oxygen; examples are fats and cholesterol.
Lipolysis
(lĭ-pol
9
ĭ-sis) Te breakdown of stored fats into glycerol and
fatty acids.
Liver
Lobed accessory organ that overlies the stomach; produces bile to
help digest fat, and serves other metabolic and regulatory functions.
Lumbar
(lum
9
bar) Portion of the back between the thorax and the pelvis.
Lumbar vertebrae
Te five vertebrae of the lumbar region of the verte-
bral column, commonly called the small of the back.
Lumen
(loo
9
min) Cavity inside a tube, blood vessel, or hollow organ.
Luteinizing hormone (LH)
(lu
9
te-in-īz
0
ing) Anterior pituitary hor-
mone that aids maturation of cells in the ovary and triggers ovulation
in females. In males, causes the interstitial endocrine cells of the testis to
produce testosterone.
Lymph
(limf) Protein-containing fluid transported by lymphatic vessels.
Lymph node
Small lymphoid organ that filters lymph; contains macro-
phages and lymphocytes.
Lymphatic system
(lim-fat
9
ik) System consisting of lymphatic vessels,
lymph nodes, and lymph; drains excess tissue fluid from the extracellular
space. Te nodes provide sites for immune surveillance.
Lymphatics
General term used to designate the lymphatic vessels that
collect and transport lymph.
Lymphocyte
Agranular white blood cell that arises from bone marrow
and becomes functionally mature in the lymphoid organs of the body.
Lysosomes
(li
9
so-sōmz) Organelles that originate from the Golgi appara-
tus and contain strong digestive enzymes.
Lysozyme
(li
9
so-zīm) Enzyme in sweat, saliva, and tears that is capable of
destroying certain kinds of bacteria.
Macromolecules
Large, complex molecules containing from 100 to over
10,000 subunits.
Macrophage
(mak
9
ro-fāj
0
) Protective cell type common in connective
tissue, lymphoid tissue, and many body organs; phagocytizes tissue cells,
bacteria, and other foreign debris; presents antigens to ± cells in the im-
mune response.
Macula
(mak
9
u-lah) (1) Receptor for linear acceleration, deceleration,
and gravity, located within the vestibule of the inner ear; (2) a colored
area or spot.
Isotonic contraction
(i
0
so-tah
9
nik) Contraction in which muscle ten-
sion remains constant at a given load, and the muscle shortens.
Isotonic solution
A solution with a concentration of nonpenetrating
solutes equal to that found in the reference cell.
Isotopes
(i
9
so-tōps) Different atomic forms of the same element, which
vary only in the number of neutrons they contain; the heavier species
tend to be radioactive.
Jejunum
(jĕ-joo
9
num) Te part of the small intestine between the duo-
denum and the ileum.
Joint (articulation)
Te junction of two or more bones.
Joint kinesthetic receptor
(kin
0
es-thet
9
ik) Receptor that provides infor-
mation on joint position and motion.
Juxtaglomerular complex (JGC)
(juks
0
tah-glo-mer
9
u-lar) Cells of the
distal part of the ascending limb of the nephron loop and afferent arteri-
ole located close to the glomerulus; involved in blood pressure regulation
(via release of the hormone renin) and autoregulation of GFR.
Karyotype
(kar
9
e-o-tīp) Te diploid chromosomal complement, typi-
cally shown as homologous chromosome pairs arranged from longest to
shortest (X and Y are arranged by size rather than paired).
Keratin
(ker
9
ah-tin) Fibrous protein found in the epidermis, hair, and
nails that makes those structures hard and water resistant; precursor is
keratohyaline.
Ketones (ketone bodies)
(ke
9
tōnz) Fatty acid metabolites; strong or-
ganic acids.
Ketosis
(kē-tō
9
sis) Excess levels of ketone bodies in blood. Called keto-
acidosis if blood pH is low.
Killer T cell
See
Cytotoxic ± cell.
Kilocalories (kcal)
See
Calorie.
Kinetic energy
(ki-net
9
ik) Te energy of motion or movement, e.g., the
constant movement of atoms, or the push given to a swinging door that
sets it into motion.
Krebs cycle
Aerobic metabolic pathway occurring within mitochondria,
in which food metabolites are oxidized and CO
2
is liberated, and coen-
zymes are reduced. Also called the citric acid cycle.
Labia
(la
9
be-ah) Lips; singular: labium.
Labor
Collective term for the series of events that expel the fetus from
the uterus.
Labyrinth
(lab
9
ĭ-rinth
0
) Bony cavities and membranes of the inner ear.
Lacrimal
(lak
9
ri-mal) Pertaining to tears.
Lactation
(lak-ta
9
shun) Production and secretion of milk.
Lacteal
(lak
9
te-al) Special lymphatic capillaries of the small intestine that
take up lipids.
Lactic acid
(lak
9
tik) Product of anaerobic metabolism, especially in
muscle.
Lacuna
(lah-ku
9
nah) A small space, cavity, or depression; lacunae in
bone or cartilage are occupied by cells.
Lamella
(lah-mel
9
ah) A layer, such as of bone matrix in an osteon of
compact bone.
Lamina
(lam
9
ĭ-nah) (1) A thin layer or flat plate; (2) the portion of a ver-
tebra between the transverse process and the spinous process.
Large intestine
Portion of the digestive tract extending from the ileoce-
cal valve to the anus; includes the cecum, appendix, colon, rectum, and
anal canal.
Larynx
(lar
9
ingks) Cartilaginous organ located between the trachea and
the pharynx; voice box.
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