(KEY-tone) product of fatty acid
metabolism that accumulates in blood during
starvation and in severe untreated diabetes
mellitus; acetoacetic acid, acetone, or B-
hydroxybutyric acid; also called
ketone body
kilocalorie (kcal)
(KIL-oh-kal-ah-ree) amount
of heat required to change the temperature of
1 L water by 1°C; calorie used in nutrition;
also called
large calorie
(KY-nase) enzyme that transfers a
phosphate (usually from ATP) to another
(ky-NEE-sin) motor protein that uses the
energy from ATP to transport attached cellular
cargo along microtubules
(kin-ess-THEE-zee-ah) sense of
movement derived from movement at a joint
(KY-nin) peptide that splits from kininogen;
facilitates vascular changes and activates pain
(ky-NIN-oh-jen) plasma protein from
which kinins are generated in an infl amed area
knee jerk
refl ex often used in clinical assessment
of nerve and muscle function; striking the
tendon just below the kneecap causes refl ex
contraction of anterior thigh muscles, which
extends the knee
Korotkoff’s sounds
(Kor-OTT-koff) sounds
caused by turbulent blood fl ow during
determination of blood pressure with a
pressurized cuff
Krebs cycle
mitochondrial metabolic pathway that
utilizes fragments derived from carbohydrate,
protein, and fat breakdown and produces
carbon dioxide, hydrogen (for oxidative
phosphorylation), and small amounts of ATP;
also called tricarboxylic acid cycle or citric acid
labeled lines
principle describing the idea that
a unique anatomical pathway of neurons
connects a given sensory receptor directly to
the CNS neurons responsible for processing
that modality and location on the body
complicated bony structure that houses
the cochlea and vestibular apparatus
(LAK-tase) small intestine enzyme that
breaks down lactose (milk sugar) into glucose
and galactose
ionized form of lactic acid
(lak-TAY-shun) production and
secretion of milk by mammary glands
(lak-TEEL) blind-ended lymph vessel in
center of each intestinal villus
lactic acid
(LAK-tik) three-carbon molecule
formed by glycolytic pathway in absence
of oxygen; dissociates to form lactate and
hydrogen ions
(LAK-tose) disaccharide composed of
glucose and galactose; also called
milk sugar
laminar fl
(LAM-ih-ner) when a fl uid (e.g.,
blood) fl ows smoothly through a tube in
concentric layers, without any turbulence
large intestine
part of the gastrointestinal tract
between the small intestine and rectum;
absorbs salts and water
(LAR-inks) part of air passageway between
pharynx and trachea; contains the vocal cords
latch state
contractile state of some smooth
muscles in which force can be maintained
for prolonged periods with very little energy
use; cross-bridge cycling slows to the point
where thick and thin fi laments are effectively
“latched” together
latent period
(LAY-tent) period lasting several
milliseconds between action potential initiation
in a muscle fi ber and beginning of mechanical
position farther from the midline
lateral inhibition
method of refi ning sensory
information in afferent neurons and ascending
pathways whereby fi bers inhibit each other,
the most active fi bers causing the greatest
inhibition of adjacent fi bers
lateral sac
enlarged region at end of each
sarcoplasmic reticulum segment; adjacent to
transverse tubule
lateral traction
force (in the lung) holding small
airways open; exerted by elastic connective
tissue linked to surrounding alveolar tissue
Law of Laplace
(lah-PLAHS) transmural pressure
difference = 2 × surface tension divided by the
radius of a hollow ball (e.g., an alveolus)
law of mass action
maxim that an increase in
reactant concentration causes a chemical
reaction to proceed in direction of product
formation; the opposite occurs with decreased
reactant concentration
L-dihydroxyphenylalanine; precursor to
dopamine formation
leak potassium channels
potassium channels that
are open when a membrane is at rest
acquisition and storage of information as
a result of experience
(LESS-ih-thin) a phospholipid
lengthening contraction
contraction as an
external force pulls a muscle to a longer length
despite opposing forces generated by the active
adjustable part of eye’s optical system, which
helps focus object’s image on retina
adipose-derived hormone that acts within
the brain to decrease appetite and increase
(LOO-koh-site) white blood cell
(LOO-koh-treens) type of
eicosanoid that is generated by lipoxygenase
pathway and functions as infl ammatory
levodopa (L-dopa)
a drug used in the treatment
of Parkinson’s disease
Leydig cell
(LY-dig) testosterone-secreting
endocrine cell that lies between seminiferous
tubules of testes; also called
interstitial cell
LH surge
large rise in luteinizing hormone
secretion by anterior pituitary about day 14 of
menstrual cycle
(luh-BEE-doh) sex drive
(LY-gand) any molecule or ion that binds
to protein surface by noncovalent bonds
ligand-gated channel
membrane channel
operated by the binding of specifi c molecules
to channel proteins
light adaptation
process by which photoreceptors
in the retina adjust to sudden bright light
light chain
pair of small polypeptides bound
to each globular head of a myosin molecule;
function is to
limbic system
(LIM-bik) interconnected brain
structures in cerebrum; involved with emotions
and learning
(LY-pase) enzyme that hydrolyzes
triglyceride to monoglyceride and fatty acids;
see also
lipoprotein lipase
(LIP-id) molecule composed primarily of
carbon and hydrogen and characterized by
insolubility in water
lipid bilayer
a sheet consisting of two layers of
amphipathic lipids; nonprotein part of a cell
(ly-POL-ih-sis) triglyceride breakdown
(lip-oh-PROH-teen) lipid aggregate
partially coated by protein; involved in lipid
transport in blood
lipoprotein lipase
capillary endothelial enzyme
that hydrolyzes triglyceride in lipoprotein to
monoglyceride and fatty acids
(ly-POX-ih-jen-ase) enzyme
that acts on arachidonic acid and leads to
leukotriene formation
large organ located in the upper right portion
of the abdomen with exocrine, endocrine, and
metabolic functions
external force acting on muscle
local control
mechanism existing within tissues
that modulates activity independent of neural
or hormonal input (e.g., blood fl ow into a local
vascular bed)
local current
movement of positive ions
toward more negative membrane region and
simultaneous movement of negative ions in
opposite direction
local homeostatic response
ik) response acting in immediate vicinity of a
stimulus, without nerves or hormones, and
having net effect of counteracting stimulus
longitudinal muscle
thin outer layer of the
intestine; contraction shortens the length of
the tube
long-loop negative feedback
inhibition of
anterior pituitary and/or hypothalamus by
hormone secreted by third endocrine gland in
a sequence
long refl
neural loop from afferents in the
gastrointestinal tract to the central nervous
system and back to nerve plexuses and
effector cells via the autonomic nervous
system; involved in the control of motility and
secretory activity
long-term depression
condition in which nerves
show reduced responses to stimuli after an
earlier stimulation
long-term memory
information stored in the
brain for prolonged periods
long-term potentiation (LTP)
process by which
certain synapses undergo long-lasting increase
in effectiveness when heavily used
loop of Henle
(HEN-lee) hairpinlike segment of
kidney nephron with
situated between proximal and distal
low-density lipoprotein (LDL)
teen) protein-lipid aggregate that is major
carrier of plasma cholesterol to cells
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