Glossary G-5to indicate the reversal of membrane polarity that
occurs during the production of action potentials in
nerve and muscle cells. Also called hypopolarization.
deposition (dep- ̆o-zish 9 on), bone The formation
of the extracellular matrix of bone by osteoblasts.
This process includes secretion of collagen and
precipitation of calcium phosphate in the form of
hydroxyapatite crystals.
detoxication (de-tok 0 s ̆ı-ka 9 shun) The reduction
of the toxic properties of molecules. This occurs
through chemical transformation of the mole cules
and takes place, to a large degree, in the liver.
diabetes insipidus (di 0 ̆a-be 9 t ̄ez in-sip 9 ̆ı-dus)
A condition in which inadequate amounts of
antidiuretic hormone (ADH) are secreted by
the posterior pituitary. It results in inadequate
reabsorption of water by the kidney tubules, and thus
in the excretion of a large volume of dilute urine.
diabetes mellitus (m ̆e-li 9 tus) The appearance
of glucose in the urine due to the presence of
high plasma glucose concentrations, even in the
fasting state. This disease is caused by either a lack
of sufficient insulin secretion or by inadequate
responsiveness of the target tissues to the effects of
insulin.
dialysis (di-al 9 ̆ı-sis) A method of removing
unwanted elements from the blood by selective
diffusion through a porous membrane.
diapedesis (di 0 ̆a-p ̄e-de 9 sis) The migration of white
blood cells through the endothelial walls of blood
capillaries into the surrounding connective tissues.
diarrhea (di 0 ̆a-re 9 ̆a) Abnormal frequency of
defecation accompanied by abnormal liquidity of the
feces.
diastole (di-as 9 t ̆o-le) The phase of relaxation in
which the heart fills with blood. Unless accompanied
by the modifier atrial, diastole refers to the resting
phase of the ventricles.
diastolic (di 0 ̆a-stol 9 ik) blood pressure The
minimum pressure in the arteries that is produced
during the phase of diastole of the heart. It is
indicated by the last sound of Korotkoff when taking
a blood pressure measurement.
diffusion (d ̆ı-fyoo 9 zhun) The net movement of
molecules or ions from regions of higher to regions
of lower concentration.
digestion The process of converting food into
molecules that can be absorbed through the intestine
into the blood.
dihydrotestosterone (di-hi 0 dro-tes-tos 9 ter-on)
(DHT) A metabolite formed in target cells from
testosterone by the enzyme 5a-reductase. DHT is
more directly responsible for many of the actions of
testosterone on its target organs.
1,25-dihydroxyvitamin (di 0 hi-drok 0 se-vi 9 t ̆a-min)
D 3 The active form of vitamin D produced within
the body by hydroxylation reactions in the liver and
kidneys of vitamin D formed by the skin. This
is a hormone that promotes the intestinal absorption
of Ca^21.
diploid (dip 9 loid) Denoting cells having two
of each chromosome, or twice the number of
chromosomes that are present in sperm or ova.
disaccharide (di-sak 9 ̆a-r ̄ıd) Any of a class of
double sugars; carbohydrates that yield two simple
sugars, or monosaccharides, upon hydrolysis.
diuretic (di 0 y ̆u-ret 9 ik) A substance that increases
the rate of urine production, thereby lowering the
blood volume.
DNA deoxyribonucleic (de-ok 0 se-ri 0 bo-noo- kle 9 ik)
acid A nucleic acid composed of nucleotide bases and
deoxyribose sugar that contains the genetic code.
dopa (do 9 p ̆a) dihydroxyphenylalanine (di 0 hi-
drok 0 se-fen 0 al- ̆a-l ̆a-n ̄ın) An amino acid formed in the
liver from tyrosine and converted to dopamine in thecytochrome (si 9 t ̆o-kr ̄om) A pigment in
mitochondria that transports electrons in the process
of aerobic respiration.
cytochrome P450 enzymes Enzymes of a
particular kind, not related to the mitochondrial
cytochromes, that metabolize a broad spectrum of
biological molecules, including steroid hormones and
toxic drugs. They are prominent in the liver where
they help in detoxication of the blood.
cytokine (si 9 to-k ̄ın) An autocrine or paracrine
regulator secreted by various tissues.
cytokinesis (si 0 to-k ̆ı-ne 9 sis) The division of the
cytoplasm that occurs in mitosis and meiosis when a
parent cell divides to produce two daughter cells.
cytoplasm (si 9 t ̆o-plaz 0 em) The semifluid part of
the cell between the cell membrane and the nucleus,
exclusive of membrane-bound organelles. It contains
many enzymes and structural proteins.
cytoskeleton (si 0 to-skel 9 ̆e-ton) A latticework of
structural proteins in the cytoplasm arranged in the
form of microfilaments and microtubules.D
Dalton’s law The statement that the total
pressure of a gas mixture is equal to the sum that
each individual gas in the mixture would exert
independently. The part contributed by each gas is
known as the partial pressure of the gas.
dark adaptation The ability of the eyes to increase
their sensitivity to low light levels over a period
of time. Part of this adaptation involves increased
amounts of visual pigment in the photoreceptors.
dark current The steady inward diffusion of Na^1
into the rods and cones when the photoreceptors are
in the dark. Stimulation by light causes this dark
current to be blocked, and thus hyperpolarizes the
photoreceptors.
declarative memory The memory of factual
information. This can be contrasted with
nondeclarative memory, which is the memory of
perceptual and motor skills.
deglutition (de-gloo-tish 9 un) The process of
swallowing.
dehydration (de 0 hi-dra 9 shun) synthesis The
bonding together of subunits to form a longer
molecule, in a reaction that also results in the
production of a molecule of water.
delayed hypersensitivity An allergic response in
which the onset of symptoms may not occur until 2
or 3 days after exposure to an antigen. Produced by
T cells, it is a type of cell-mediated immunity.
dendrite (den 9 dr ̄ıt) A relatively short, highly
branched neural process that carries electrical
activity to the cell body.
dendritic (den-drit 9 ik) cells The most potent
antigen-presenting cells for the activation of helper
T lymphocytes. The dendritic cells originate in the
bone marrow and migrate through the blood and
lymph to lymphoid organs and to nonlymphoid
organs such as the lungs and skin.
denervation (de 0 ner-va 9 shun) hypersensitivity
The increased sensitivity of smooth muscles to neural
stimulation after their innervation has been blocked
or removed for a period of time.
deoxyhemoglobin (de-ok 0 se-he 0 m ̄o-glo 9 bin) The
form of hemoglobin in which the heme groups are in
the normal reduced form but are not bound to a gas.
Deoxyhemoglobin is produced when oxyhemoglobin
releases oxygen.
depolarization (de-po 0 lar- ̆ı-za 9 shun) The loss of
membrane polarity in which the inside of the cell
membrane becomes less negative in comparison to
the outside of the membrane. The term is also usedcotransport Also called coupled transport or
secondary active transport. Carrier-mediated
transport in which a single carrier transports an ion
(e.g., Na^1 ) down its concentration gradient while
transporting a specific molecule (e.g., glucose)
against its concentration gradient. The hydrolysis of
ATP is indirectly required for cotransport because
it is needed to maintain the steep concentration
gradient of the ion.
countercurrent exchange The process that occurs
in the vasa recta of the renal medulla in which
blood flows in U-shaped loops. This allows sodium
chloride to be trapped in the interstitial fluid while
water is carried away from the kidneys.
countercurrent multiplier system The interaction
that occurs between the descending limb and the
ascending limb of the loop of Henle in the kidney.
This interaction results in the multiplication of the
solute concentration in the interstitial fluid of the
renal medulla.
creatine phosphate (kre 9 ̆a-tin fos 9 f ̄at) An organic
phosphate molecule in muscle cells that serves as a
source of high-energy phosphate for the synthesis of
ATP; also called phosphocreatine.
creatine phosphokinase (kre 9 a-ten fos-fo-ki 9 nas)
(CPK) An enzyme that forms creatine phosphate
from creatine and ATP. It also catalyzes the reverse
reaction, in which creatine phosphate donates its
phosphate group to ADP to form ATP. This reaction
generates ATP rapidly when muscles are exercising.
Also known as creatine kinase (CK).
creatinine (kre-at 9 i-nen) A molecule formed
from muscle creatine that is maintained at a normal
plasma concentration by the kidneys, which filter the
creatinine into the urine. Because the creatinine is
not reabsorbed and is only slightly secreted, its renal
plasma clearance is often used as a measure of the
glomerular filtration rate (GFR).
CREB An acronym for cyclic AMP response
element binding protein. CREB is a transcription
factor that activates genes important for learning and
long-term potentiation.
cremasteric (krem-as-ter 9 ik) reflex Contraction
of the cremaster muscles retracts the testes closer to
the body cavity. This contraction may be elicited as
a reflex response to the gentle stroking of a male’s
inner thigh.
crenation (kr ̆ı-na 9 shun) A notched or scalloped
appearance of the red blood cell membrane caused
by the osmotic loss of water from the cells.
cretinism (kr ̄et 9 n-iz 0 em) A condition caused
by insufficient thyroid secretion during prenatal
development or the years of early childhood. It
results in stunted growth and inadequate mental
development.
cryptorchidism (krip-tor 9 k ̆ı-diz 0 em) A
developmental defect in which the testes fail to
descend into the scrotum, and instead remain in the
body cavity.
curare (koo-r ̆a-re) A chemical derived from
plant sources that causes flaccid paralysis by
blocking ACh receptor proteins in muscle cell
membranes.
Cushing’s syndrome Symptoms caused by
hypersecretion of adrenal steroid hormones
as a result of tumors of the adrenal cortex or ACTH-
secreting tumors of the anterior pituitary.
cyanosis (si 9 a-no ̆ 0 sis) A bluish discoloration
of the skin or mucous membranes due to
excessive concentration of deoxyhemoglobin;
indicative of inadequate oxygen concentration in
the blood.
cyclins (si 9 klinz) A group of proteins that promote
different phases of the cell cycle by activating
enzymes called cyclin-dependant kinases.fox36375_glo_G1-G19.indd 5fox36375_glo_G1-G19.indd 5 2/4/15 12:29 PM2/4/15 12:29 PM