Structure:
Target tissues or organs, where endocrine hormones from target
glands produce their effects, are distributed throughout the body.
Each tissue affected has a way of selectively
binding or otherwise retaining the hormone destined to affect that
tissue. For most target tissues, the cell membrane is the site of active
attachment. Endocrine hormones may be in one of several different families
of chemicals; these include proteins, peptides, amino acids, biogenic amines,
and steroid hormones. At least sixteen hormones are produced by the target
glands. The principal or most active of the hormones secreted are growth
hormone, thyroxine, calcitonin,
parathormone, insulin,
glucagon, somatostatin,
aldosterone, corticosterone,
dehydroepiandrosterone-sulfate, epinephrine,
norepinephrine, testosterone,
estradiol, androstenedione,
and progesterone. Hundreds of metabolites
of these hormones, sometimes more potent than the one secreted, can be
found in the blood or cells of the body.
Function:
Target tissues attract and accumulate hormones from the circulation, activate
the second messenger system for the production
of cyclic AMP for activating selective protein kinases, using DNA/mRNA
nucleoproteins for synthesizing new proteins. The proteins produced may
be structural, enzymatic, binding, or other proteins.
