Labial frenulum (LA-be-al FREN-Q-lum) A medial fold of mucous mem-
brane between the inner surface of the lip and the gums.
Labor The process of giving birth in which a fetus is expelled from
the uterus through the vagina.
Lacrimal canal (LAK-ri-mal) A duct, one on each eyelid, beginning
at the punctum at the medial margin of an eyelid and conveying
tears medially into the nasolacrimal sac.
Lacrimal gland Secretory cells, located at the superior anterolateral
portion of each orbit, that secrete tears into excretory ducts that
open onto the surface of the conjunctiva.
Lacrimal sac The superior expanded portion of the nasolacrimal
duct that receives the tears from a lacrimal canal.
Lactation (lak-TA-shun) The secretion and ejection of milk by the
Lacteal (LAK-te-al) One of many lymphatic vessels in villi of the
intestines that absorb triglycerides and other lipids from digested
Lacuna (la-KOO-na) A small, hollow space, such as that found in
bones in which the osteocytes lie.
P lu r a l
is lacunae (la-KOO-ne).
Lamellae (la-MEL-e) Concentric rings of hard, calcified extracellular
matrix found in compact bone.
Lamina propria (PRO-pre-a) The connective tissue layer of a mucosa.
Langerhans cell (LANG-er-hans) Epidermal dendritic cell that func-
tions as an antigen-presenting cell (APC) during an immune
Lanugo (la-NOO-go) Fine downy hairs that cover the fetus.
Large intestine The portion of the gastrointestinal tract extending
from the ileum of the small intestine to the anus, divided structur-
ally into the cecum, colon, rectum, and anal canal.
Laryngopharynx (la-rin'-go-FAR-inks) The inferior portion of the
pharynx, extending downward from the level of the hyoid bone
that divides posteriorly into the esophagus and anteriorly into the
larynx. Also called the hypopharynx.
Larynx (LAR-inks) The voice box, a short passageway that connects
the pharynx with the trachea.
Lateral (LAT-er-al) Farther from the midline of the body or a
Lateral ventricle (VEN-tri-kul) A cavity within a cerebral hemisphere
that communicates with the lateral ventricle in the other cerebral
hemisphere and with the third ventricle by way of the interven-
Leg The part of the lower limb between the knee and the ankle.
Lens A transparent organ constructed of proteins (crystallins) lying
posterior to the pupil and iris of the eyeball and anterior to the
Lesion (LE-zhun) Any localized, abnormal change in a body tissue.
Leukemia (loo-KE-me-a) A malignant disease of the blood-forming
tissues characterized by either uncontrolled production and
accumulation of immature leukocytes in which many cells fail to
reach maturity (acute) or an accumulation of mature leukocytes
in the blood because they do not die at the end of their normal
life span (chronic).
Leukocyte (LOO-ko-sTt) A white blood cell.
Leukocytosis (loo'-ko-sT-TO-sis) An increase in the number of white
blood cells, above 10,000 per |iL, characteristic of many infec-
tions and other disorders.
Leukopenia (loo-ko-PE-ne-a) A decrease in the number of white
blood cells below 5000 cells per |iL.
Leydig cell (LT-dig) A type of cell that secretes testosterone; located
in the connective tissue between seminiferous tubules in a
mature testis. Also known as interstitial cell of Leydig.
Libido (li-BE-do) Sexual desire.
Ligament (LIG-a-ment) Dense regular connective tissue that attaches
bone to bone.
Ligand (LT-gand) A chemical substance that binds to a specific
Limbic system A part of the forebrain, sometimes termed the
visceral brain, concerned with various aspects of emotion and
behavior; includes the limbic lobe, dentate gyrus, amygdala,
septal nuclei, mammillary bodies, anterior thalamic nucleus,
olfactory bulbs, and bundles of myelinated axons.
Lipase An enzyme that splits fatty acids from triglycerides and
Lipid (LIP-id) An organic compound composed of carbon, hydrogen,
and oxygen that is usually insoluble in water, but soluble in alco-
hol, ether, and chloroform; examples include triglycerides (fats
and oils), phospholipids, steroids, and eicosanoids.
Lipid bilayer Arrangement of phospholipid, glycolipid, and choles-
terol molecules in two parallel layers in which the hydrophilic
"heads" face outward and the hydrophobic "tails" face inward;
found in cellular membranes.
Lipogenesis (li-po-GEN-e-sis) The synthesis of triglycerides.
Lipolysis (lip-OL-i-sis) The splitting of fatty acids from a triglyceride or
Lipoprotein (lip'-o-PRO-ten) One of several types of particles contain-
ing lipids (cholesterol and triglycerides) and proteins that make it
water soluble for transport in the blood; high levels of low-density
lipoproteins (LDLs) are associated with increased risk of athero-
sclerosis, whereas high levels of high-density lipoproteins (HDLs)
are associated with decreased risk of atherosclerosis.
Liver Large organ under the diaphragm that occupies most of the
right hypochondriac region and part of the epigastric region.
Functionally, it produces bile and synthesizes most plasma
proteins; interconverts nutrients; detoxifies substances; stores
glycogen, iron, and vitamins; carries on phagocytosis of worn-out
blood cells and bacteria; and helps synthesize the active form of
Lordosis (lor-DO-sis) An exaggeration of the lumbar curve of the
vertebral column. Also called hollow back.
Lower limb The appendage attached at the pelvic (hip) girdle, con-
sisting of the thigh, knee, leg, ankle, foot, and toes. Also called
Lumbar (LUM-bar) Region of the back and side between the ribs and
Lumbar plexus (PLEK-sus) A network formed by the anterior (ventral)
branches of spinal nerves L1 through L4.