lower esophageal sphincter
smooth muscle
of last portion of esophagus; can close off
esophageal opening into the stomach
lower motor neurons
neurons that synapse
directly onto muscle cells and stimulate their
L-type calcium channel
voltage-gated channel
permitting calcium entry into heart cells during
the action potential; L denotes the long-lasting
open time that characterizes these channels
(LOO-men) space in hollow tube or organ
(LOO-min-ul) pertaining to lumen
luminal membrane
portion of plasma membrane
facing the lumen; also called
lung compliance (C
(come-PLY-ance) change
in lung volume caused by a given change in
transpulmonary pressure; the greater the lung
compliance, the more stretchable the lung wall
luteal phase
(LOO-tee-al) last half of menstrual
cycle following ovulation; corpus luteum is
active ovarian structure
luteinizing hormone (LH)
ing) peptide gonadotropic hormone secreted
by anterior pituitary; rapid increase in females
at midmenstrual cycle initiates ovulation;
stimulates Leydig cells in males
(limf) fl uid in lymphatic vessels
lymphatic capillary
(lim-FAT-ik) smallest-
diameter vessel type of the lymphatic system;
site of entry of excess extracellular fl uid
lymphatic system
(lim-FAT-ik) network of vessels
that conveys lymph from tissues to blood and
to lymph nodes along these vessels
lymphatic vessel
any vessel of the lymph system in
which excess interstitial fl uid is transported and
returned to the circulation; along the way, the
fl uid (lymph) passes through lymph nodes
lymph node
small organ, containing lymphocytes,
located along lymph vessel; a site of
lymphocyte cell division and initiation of
specifi c immune responses
(LIMF-oh-site) type of leukocyte
responsible for specifi c immune defenses; B
cells, T cells, and NK cells
lymphocyte activation
cell division and
differentiation of lymphocytes following
antigen binding
lymphoid organ
(LIMF-oid) bone marrow,
lymph node, spleen, thymus, tonsil, or
aggregate of lymphoid follicles;
see also
lymphoid organ, secondary lymphoid organ
(LY-soh-some) membrane-bound cell
organelle containing digestive enzymes in a
highly acid solution that break down bacteria,
large molecules that have entered the cell, and
damaged components of the cell
large molecule composed of up
to thousands of atoms
(MAK-roh-fahje) cell that
phagocytizes foreign matter, processes
it, presents antigen to lymphocytes, and
secretes cytokines (monokines) involved in
infl ammation, activation of lymphocytes, and
systemic acute phase response to infection
or injury;
see also
activated macrophage,
macrophage-like cell
macrophage-like cell
one of several cell types
that exert functions similar to those of
macula densa
(MAK-you-lah DEN-sah)
specialized sensor cells of renal tubule at end of
loop of Henle; component of juxtaglomerular
major histocompatibility complex (MHC)
group of genes that code for major
histocompatibility complex proteins, which are
important for specifi c immune function
a decrease in the absorption
of minerals, vitamins, and nutrients in the
gastrointestinal tract
(mul-LARE-ee-uh) parasitic blood disease
caused by a protozoan spread by the bites of
infected mosquitoes
one of three bones in the inner ear
that transmit movements of the tympanic
membrane to the inner ear
mammary gland
milk-secreting gland in breast
initial step in leukocyte action in
infl amed tissues, in which leukocytes adhere to
the endothelial cell
fundamental property of an object equivalent
to the amount of matter in the object
mass movement
contraction of large segments of
colon; propels fecal matter into rectum
mast cell
tissue cell that releases histamine and
other chemicals involved in infl ammation
matrix (mitochondrial)
the innermost
mitochondrial compartment
maximal oxygen consumption (V
rate of oxygen use as physical exertion is
increased; increments in workload above this
point must be fueled by anaerobic metabolism
maximal tubular capacity (
mean arterial pressure (MAP)
average blood
pressure during cardiac cycle; approximately
diastolic pressure plus one-third pulse pressure
mechanically gated channel
ion channel that is opened or closed by
deformation or stretch of the plasma
sensory neuron specialized to respond to
mechanical stimuli such as touch receptors in
the skin and stretch receptors in muscle
median eminence
(EM-ih-nence) region at base
of hypothalamus containing capillary tufts into
which hypophysiotropic hormones are secreted
(mee-dee-uh-STY-num) membrane
separating right and left thoracic compartments
(MEE-dee-ate) bring about
mediated transport
movement of molecules
across membrane by binding to protein
transporter; characterized by specifi city,
competition, and saturation; includes facilitated
diffusion and active transport
(meh-DUL-ah) innermost portion of
an organ;
adrenal medulla,
medulla oblongata
medulla oblongata
(ob-long-GOT-ah) part of
the brainstem closest to the spinal cord
medullary cardiovascular center
cardiovascular center
medullary collecting duct
terminal component
of the nephron in which vasopressin-sensitive
passive water reabsorption occurs
medullary inspiratory center
neurons in the
medulla oblongata that set the pace for
inspiration; their rate of fi ring is rhythmical but
can be overridden by conscious control
(meg-ah-KAR-ee-oh-site) large
bone marrow cell that gives rise to platelets
(my-OH-sis) process of cell division
leading to gamete (sperm or egg) formation;
daughter cells receive only half the
chromosomes present in original cell
meiotic arrest
state of primary oocytes from fetal
development until puberty, after which meiosis
is completed
membrane attack complex (MAC)
group of
complement proteins that form channels in
microbe surface and destroy microbe
membrane potential
voltage difference between
inside and outside of cell
declarative memory, procedural
memory, working memory
memory cell
B cell or T cell that differentiates
during an initial infection and responds rapidly
during subsequent exposure to same antigen
memory encoding
processes by which an
experience is transformed to a memory of that
(MEN-ark-ee) onset, at puberty, of
menstrual cycling in women
(men-IN-jees) protective membranes
that cover brain and spinal cord
(MEN-ah-paws) cessation of
menstrual cycling in middle age
menstrual cycle
(MEN-stroo-al) cyclical rise
and fall in female reproductive hormones and
processes, beginning with menstruation
menstrual phase
time during menstrual cycle in
which menstrual blood is present
(men-stroo-AY-shun) fl ow of
menstrual fl uid from uterus; also called
menstrual period
an alcohol derived from mint oil that
activates ion channels found in temperature
receptors that sense cool temperatures
mesangial cell
modifi ed smooth-muscle cell that
surrounds renal glomerular capillary loops;
they help to control glomerular fi ltration rate
mesolimbic dopamine pathway
neural pathway
through the limbic system that uses dopamine
as its neurotransmitter and is involved in reward
messenger RNA (mRNA)
ribonucleic acid that
transfers genetic information for a protein’s
amino acid sequence from DNA to ribosome
metabolic acidosis
(met-ah-BOL-ik ass-ih-DOH-
sis) acidosis due to the buildup of acids other
than carbonic acid (from carbon dioxide)
metabolic alkalosis
(al-kah-LOH-sis) alkalosis
resulting from the removal of hydrogen ions by
mechanisms other than respiratory removal of
carbon dioxide
metabolic end product
fi nal molecule produced
by a metabolic reaction or series of reactions
metabolic pathway
sequence of enzyme-mediated
chemical reactions by which molecules are
synthesized and broken down in cells
metabolic rate
total body energy expenditure per
unit time
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