G-12 glossary
immunity The body’s overall ability to resist and combat any
substance foreign to itself.
immunization Various processes, including vaccination, that
promote increased immunity against specific diseases.
immunodeficiency Disorder in which a person’s immune
system is weakened or absent.
immunoglobulin Ig; any of the five classes of antibodies
that participate in defense and immune responses. Examples
are IgM antibodies (first to be secreted during immune
responses) and IgG antibodies (which activate complement
proteins and neutralize many toxins).
immunological tolerance The lack of an immune response
against normal body cells.
immunotherapy Procedures that enhance a person’s immu-
nological defenses against tumors or certain pathogens.
implantation Series of events in which a blastocyst (pre-
embryo) invades the endometrium (lining of the uterus) and
becomes embedded there.
independent assortment Genetic principle that each gene
pair tends to assort into gametes independently of other gene
pairs located on nonhomologous chromosomes.
induced-fit model According to this model, a surface region
of each substrate has chemical groups that are almost but not
quite complementary to chemical groups in an active site.
inflammation Process in which, in response to tissue dam-
age or irritation, phagocytes and plasma proteins, including
complement proteins, leave the bloodstream, then defend and
help repair the tissue. Occurs during both nonspecific and
specific (immune) defense responses.
innate immunity The body’s inborn, preset immune
responses, which act quickly when tissue is damaged or
microbes have invaded.
inner cell mass In early development, a clump of cells in the
blastocyst that will give rise to the embryonic disk.
inorganic compound Compound that does not contain both
carbon and hydrogen.
insertion The end of a muscle that is attached to the bone
that moves most when the muscle contracts.
inspiration The drawing of air into the lungs; inhaling.
integration, neural See synaptic integration.
integrator Of homeostatic systems, a control point where dif-
ferent bits of information are pulled together in the selection
of a response. The brain is an example.
integument [L. integere, to cover] The organ system that pro-
vides a protective body covering; in humans, the skin, oil and
sweat glands, hair, and nails.
interferon Protein produced by T cells that interferes with
viral replication. Some interferons also stimulate the tumor-
killing activity of macrophages.
interleukin One of a variety of chemical communication
signals—secreted by macrophages and helper T cells—that
drive immune responses.Human Genome Project (HGP) A research project in which
the estimated three billion nucleotides present in the DNA of
human chromosomes were sequenced.
humerus The long bone of the upper arm.
hydrocarbon A molecule having only hydrogen atoms
attached to a carbon backbone.
hydrogen bond A weak attraction between an electronega-
tive atom and a hydrogen atom that is already taking part in
a polar covalent bond.
hydrogen ion A free (unbound) proton; a hydrogen atom
that has lost its electron and so bears a positive charge (H+).
hydrolysis reaction (high-drawl-ih-sis) [L. hydro, water, and
Gk. lysis, loosening or breaking apart] Enzyme-driven reac-
tion in which covalent bonds break, splitting a molecule into
two or more parts, and H+ and OH– (derived from a water
molecule) become attached to the exposed bonding sites.
hydrophilic [Gk. philos, loving] Characteristic of a polar sub-
stance that is attracted to the polar water molecule and so dis-
solves easily in water. Sugars are examples.
hydrophobic [Gk. phobos, dreading] Characteristic of a non-
polar substance that is repelled by the polar water molecule
and so does not readily dissolve in water. Oil is an example.
hydroxide ion Ionized compound of one oxygen and one
hydrogen atom (OH–).
hyperplasia An abnormal enlargement of tissue that leads to
a tumor.
hypertension Chronically elevated blood pressure.
hyperthermia Condition in which the body core temperature
rises above the normal range.
hypertonic Having a greater concentration of solutes relative
to another fluid.
hypodermis A subcutaneous layer having stored fat that
helps insulate the body; although not part of skin, it anchors
skin while allowing it some freedom of movement.
hypothalamus [Gk. hypo, under, and thalamos, inner cham-
ber] A brain center that monitors visceral activities (such as
salt–water balance and temperature control) and that influ-
ences related forms of behavior (as in hunger, thirst, and sex).
hypothermia Condition in which the body core temperature
falls below the normal range.
hypothesis A possible explanation of a specific
phenomenon.
hypotonic Having a lower concentration of solutes relative
to another fluid.
ileum Final section of the small intestine, where absorption is
completed and residues move toward the large intestine.
immune system Interacting white blood cells that defend
the body through self/nonself recognition, specificity, and
memory. T and B cell antigen receptors ignore the body’s own
cells yet collectively recognize at least a billion specific threats.
Some B and T cells formed in a primary response are set aside
as memory cells for future battles with the same antigen.
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