Noradrenaline
A hormone, produced by the medulla of the adrenal gland, that increases the concentration
of glucose in the blood, raises blood pressure and heartbeat rate, and increases muscular
power and resistance to fatigue; also one of the principal neurotransmitters; also called
norepinephrine.
Norepinephrine
A substance, C 8 H 11 NO 3 , both a hormone and neurotransmitter, secreted by the adrenal
medulla and the nerve endings of the sympathetic nervous system to cause vasoconstriction
and increases in heart rate, blood pressure, and the sugar level of the blood. Also called
noradrenaline.
Norm of reaction
The range of phenotypic possibilities for a single genotype, as influenced by the
environment.
Nostril
Either f the external opening of the nose.
Notochord
A longitudinal, flexible rod formed from dorsal mesoderm and located between the gut and
the nerve cord in all chordate embryos.
Nuclear envelope
The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm.
Nucleic acid
A polymer consisting of many nucleotide monomers; serves as a blueprint for proteins and,
through the actions of proteins, for all cellular activities. The two types are DNA and RNA.
Nuclear
The scientific study of the forces, reactions, and internal structures of atomic nuclei.
Nuclear envelope
The double-layered membrane enclosing the nucleus of a cell. Also called nuclear envelope.
Nuclear lamina
A protein meshwork lining the inner surface of the nuclear envelope
Nuclear membrane
The double-layered membrane enclosing the nucleus of a cell. Also called nuclear envelope
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