Glossary
G-7
Differential white blood cell count
Diagnostic test to determine relative
proportion of individual leukocyte types.
Diffusion
(dĭ-fu
9
zhun) Te spreading of particles in a gas or solution
with a movement toward uniform distribution of particles; driven by
kinetic energy.
Digestion
A series of catabolic steps in which complex food molecules
are broken down to their building blocks by enzymes.
Digestive system
System that processes food into absorbable units and
eliminates indigestible wastes.
Dipeptide
A combination of two amino acids united by means of a pep-
tide bond.
Diploë
(dip
9
lo-e) Te internal layer of spongy bone in flat bones.
Diploid chromosomal number
Te chromosomal number characteris-
tic of an organism, symbolized as 2
n
; twice the chromosomal number (
n
)
of the gamete; in humans, 2
n
5
46.
Diplopia
(dĭ-plo
9
pe-ah) Double vision.
Dipole
(polar molecule) Nonsymmetrical molecules that contain electri-
cally unbalanced atoms.
Disaccharide
(di-sak
9
ah-rīd
0
, di-sak
9
ah-rid) Literally, double sugar; e.g.,
sucrose, lactose.
Dislocation (luxation)
Occurs when bones are forced out of their nor-
mal alignment at a joint.
Displacement (exchange) reaction
Chemical reaction in which bonds are
both made and broken; atoms become combined with different atoms.
Distal
(dis
9
tul) Away from the attached end of a limb or the origin of a
structure.
Diuretics
(di
0
u-ret
9
iks) Chemicals that enhance urinary output.
Diverticulum
(di
0
ver-tik
9
u-lum) A pouch or sac in the walls of a hollow
organ or structure.
DNA (deoxyribonucleic acid)
(de-ok
0
sĭ-ri
0
bo-nu-kla
9
ik) A nucleic acid
found in all living cells; it carries the organism’s hereditary information.
DNA replication
Process that occurs before cell division; ensures that all
daughter cells have identical genes.
Dominant traits
Occurs when one allele masks or suppresses the ex-
pression of its partner.
Dominant-recessive inheritance
Reflects the interaction of dominant
and recessive alleles.
Dorsal
(dor
9
sul) Pertaining to the back; posterior.
Dorsal root ganglion
Peripheral collection of cell bodies of first-order
afferent neurons whose central axons enter the spinal cord.
Double helix
Te secondary structure assumed by two strands of DNA,
held together throughout their length by hydrogen bonds between bases
on opposite strands.
Duct (dukt)
A canal or passageway; a tubular structure that provides an
exit for the secretions of a gland, or for conducting any fluid.
Ductus (vas) deferens
Extends from the epididymis to the urethra; pro-
pels sperm into the urethra by peristalsis during ejaculation.
Duodenum
(du
0
o-de
9
num) First part of the small intestine.
Dura mater
(du
9
rah ma
9
ter) Outermost and toughest of the three mem-
branes (meninges) covering the brain and spinal cord.
Dynamic equilibrium
Sense that reports on angular (rotatory) accelera-
tion or deceleration of the head in space.
Dyskinesia
(dis-kĭ-ne
9
ze-ah) Disorders of muscle tone, posture, or in-
voluntary movements.
Dyspnea
(disp-ne
9
ah) Difficult or labored breathing; air hunger.
Cytosine (C)
(si
9
to-sēn) Nitrogen-containing base that is part of a
nucleotide structure.
Cytoskeleton
Literally, cell skeleton. An elaborate series of rods running
through the cystol, supporting cellular structures and providing the ma-
chinery to generate various cell movements.
Cytosol
Viscous, semitransparent fluid substance of cytoplasm in which
other elements are suspended.
Cytotoxic T cell (T
C
cell)
Effector ± cell that directly kills foreign cells, cancer
cells, or virus-infected body cells by inducing apoptosis (cell suicide).
Deamination
(de
0
am-ih-na
9
shun) Removal of an amine group from an
organic compound.
Decomposition reaction
Chemical reaction in which a molecule is bro-
ken down into smaller molecules or its constituent atoms.
Defecation
(def
0
ih-ka
9
shun) Elimination of the contents of the bowels
(feces).
Deglutition
(deg
0
loo-tish
9
un) Swallowing.
Dehydration
(de
0
hi-dra
9
shun) Condition of excessive water loss.
Dehydration synthesis
Process by which a large molecule is synthesized
by removing water and covalently bonding smaller molecules together.
Dendrite
(den
9
drīt) Branching neuron process that serves as a receptive,
or input, region; transmits an electrical signal toward the cell body.
Dendritic cells
Protective cells that phagocytize antigens, migrate to
lymph nodes, and present the antigen to ± cells, causing them to activate
and mount an immune response; those in the skin are sometimes called
Langerhans cells.
Depolarization
(de-po
0
ler-ah-za
9
shun) Loss of a state of polarity; loss or
reduction of negative membrane potential.
Dermatome
(der
9
mah-tōm) Portion of somite mesoderm that forms
the dermis of the skin; also the area of skin innervated by the cutaneous
branches of a single spinal nerve.
Dermis
Layer of skin deep to the epidermis; composed mostly of dense
irregular connective tissue.
Desmosome
(dez
9
muh-sōm) Cell junction composed of thickened
plasma membranes joined by filaments.
Diabetes insipidus
(di
0
ah-be
9
tēz in-sih
9
pih-dus) Disease characterized
by passage of a large quantity of dilute urine plus intense thirst and dehy-
dration caused by inadequate release of antidiuretic hormone (ADH).
Diabetes mellitus (DM)
(meh-li
9
tus) Disease caused by deficient insulin
release or by insulin resistance, leading to inability of the body cells to use
carbohydrates.
Dialysis
(di-al
9
ah-sis) Diffusion of solute(s) through a semipermeable
membrane.
Diapedesis
(di
0
ah-pĕ-de
9
sis) Passage of white blood cells through intact
vessel walls into tissue.
Diaphragm
(di
9
ah-fram) (1) Any partition or wall separating one area
from another; (2) a muscle that separates the thoracic cavity from the
lower abdominopelvic cavity.
Diaphysis
(di-af
9
ĭ-sis) Elongated sha² of a long bone.
Diarthrosis
(di
0
ar-thro
9
sis) Freely movable joint.
Diastole
(di-as
9
to-le) Period of the cardiac cycle when either the ven-
tricles or the atria are relaxing.
Diastolic pressure
(di-as-tah
9
lik) Arterial blood pressure reached during
or as a result of diastole; lowest level of any given cardiac cycle.
Diencephalon (interbrain)
(di
0
en-seh
9
fuh-lon) Tat part of the fore-
brain between the cerebral hemispheres and the midbrain including the
thalamus, the epithalamus, and the hypothalamus.
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