Glossary 569portion of the refraction pathway for the focusing of light
rays (Chapter 9).
Lesion(LEE-zhun) An area of pathologically altered tissue;
an injury or wound (Chapter 5).
Leukemia(loo-KEE-mee-ah) Malignancy of blood-form-
ing tissues, in which large numbers of immature and non-
functional white blood cells are produced (Chapter 11).
Leukocyte(LOO-koh-sight) White blood cell; the five
kinds are neutrophils, eosinophils, basophils, lympho-
cytes, and monocytes (Chapter 11).
Leukocytosis(LOO-koh-sigh-TOH-sis) An elevated white
blood cell count, often an indication of infection
(Chapter 11).
Leukopenia(LOO-koh-PEE-nee-ah) An abnormally low
white blood cell count; may be the result of aplastic ane-
mia, or a side effect of some medications (Chapter 11).
Leukotrienes(LOO-koh-TRY-ens) Chemicals produced
by basophils and mast cells from the phospholipids of
their cell membranes; they increase capillary permeabil-
ity and attract WBCs during inflammation (Chapter 14).
Ligament(LIG-uh-ment) A fibrous connective tissue struc-
ture that connects bone to bone (Chapter 6).
Lipase(LY E-pays) A digestive enzyme that breaks down
emulsified fats to fatty acids and glycerol; secreted by the
pancreas (Chapter 16).
Lipid(LIP-id) An organic chemical insoluble in water;
includes true fats, phospholipids, and steroids (Chap-
ter 2).
Lipoprotein(li-poh-PRO-teen) A large molecule that is a
combination of proteins, triglycerides, and cholesterol;
formed by the liver to circulate lipids in the blood
(Chapter 16).
Lithotripsy(LITH-oh-TRIP-see) Crushing of gallstones
or renal calculi by an instrument that uses ultrasonic
waves applied to the exterior of the body (Chapter 16).
Liver(LIV-er) The organ in the upper right and center of
the abdominal cavity; secretes bile for the emulsification
of fats in digestion; has many other functions related to
the metabolism of nutrients and the composition of
blood (Chapter 16).
Liver lobule(LIV-er LAH-byool) The structural unit of
the liver; a columnar hexagon of liver cells and sinusoids
surrounding a central vein; includes the smallest bile
ducts (Chapter 16).
Localized infection(LOH-kuhl-IZ’D) An infection con-
fined to one body organ or site (Chapter 22).
Longitudinal section (LAWNJ-i-TOO-din-uhl SEK-
shun) A plane or cut along the long axis of an organ or
the body (Chapter 1).
Loop of Henle(LOOP of HEN-lee) The part of a renal
tubule that extends from the proximal convoluted tubule
to the distal convoluted tubule (Chapter 18).
Lordosis(lor-DOH-sis) An exaggerated lumbar curvature
of the vertebral column (Chapter 6).Lower esophageal sphincter (e-SOF-uh-JEE-uhl
SFINK-ter) The circular smooth muscle at the lower
end of the esophagus; prevents backup of stomach con-
tents (Syn.—cardiac sphincter) (Chapter 16).
Lower respiratory tract(LOH-er RES-pi-rah-TOR-ee
TRAKT) The respiratory organs located within the
chest cavity (Chapter 15).
Lumbar puncture(LUM-bar PUNK-chur) A diagnostic
procedure that involves removal of cerebrospinal fluid
from the lumbar meningeal sac to assess the pressure and
constituents of cerebrospinal fluid (Chapter 8).
Lumbar vertebrae(LUM-bar VER-te-bray) The five large
vertebrae in the small of the back (Chapter 6).
Lungs(LUHNGS) The paired organs in the thoracic cav-
ity in which gas exchange takes place between the air in
the alveoli and the blood in the pulmonary capillaries
(Chapter 15).
Luteinizing hormone (LH or ICSH)(LOO-tee-in-EYE-
zing) A gonadotropic hormone produced by the anterior
pituitary gland that, in men, stimulates secretion of
testosterone by the testes or, in women, stimulates ovula-
tion and secretion of progesterone by the corpus luteum
in the ovary (Chapter 10).
Lymph(LIMF) The water found within lymphatic vessels
(Chapter 2).
Lymph node(LIMF NOHD) A small mass of lymphatic
tissue located along the pathway of a lymph vessel; pro-
duces some lymphocytes and destroys pathogens in the
lymph (Chapter 14).
Lymph nodule(LIMF NAHD-yool) A small mass of lym-
phatic tissue located in a mucous membrane; destroys
pathogens that penetrate mucous membranes (Chapter
14).
Lymphatic tissue(lim-FAT-ik TISH-yoo) A hemopoietic
tissue that produces some lymphocytes and in which lym-
phocytes mature and are activated; found in the spleen
and lymph nodes and nodules (Chapter 11).
Lymphocyte(LIM-foh-sight) A type of white blood cell
(agranular); T cells and B cells are involved in the specific
responses of adaptive immunity; natural killer cells are
nonspecific and are part of innate immunity (Chapter
11).
Lysosome(LY E-soh-zome) A cell organelle found in the
cytoplasm; contains enzymes that digest damaged cell
parts or material ingested by the cell (Chapter 3).
Lysozyme(LY E-soh-zyme) An enzyme in tears and saliva
that inhibits the growth of bacteria in these fluids
(Chapter 9).—M—
Macrophage(MAK-roh-fahj) A phagocytic cell derived
from monocytes that contributes to both innate
and adaptive immunity. Capable of phagocytosis of30Scanlon(p3) Glossary 8/17/06 11:08 AM Page 569