Encyclopedia of Health and Medicine

THE ENDOCRINE SYSTEM
The endocrine glands produce hormones, chemical messengers that regulate many functions within the body. Physician
specialists who treat endocrine conditions are endocrinologists and neuroendocrinologists. This section, “The
Endocrine System,” presents a discussion of the endocrine glands and other structures, the hormones they produce and
their functions, an overview of endocrine health and disorders, and entries about the health conditions that involve
the endocrine system.
Structures of the Endocrine System
HYPOTHALAMUS
PITUITARY GLAND
anterior pituitary lobe
posterior pituitary lobe
PINEAL GLAND
THYROID GLAND
PARATHYROID GLANDS
THYMUS
ISLETS OF LANGERHANS
ADRENAL GLANDS
adrenal cortex
adrenal medulla
OVARIES (female)
TESTICLES (male)
Functions of the Endocrine System
The endocrine system and the NERVOUS SYSTEM
work in tandem to direct and regulate the myriad
functions of the body, the nervous system
through electrical impulses that travel along the
nerves and the endocrine system via chemical
messengers called hormones. Endocrine glands,
sometimes called ductless glands, produce hormones.
The endocrine glands release their hormones
directly into the bloodstream, and the
bloodstream transports them to the cells. Cells
throughout the body contain receptors for specific
hormones, so even though hormones circulate
freely through the blood they affect the functions
of only the cells that have receptors for them.
The endocrine glands may be clearly defined or
loosely configured structures and are in numerous
locations throughout the body. Some collections
of endocrine cells inhabit other tissues and organs,
such as those in the STOMACH and SMALL INTESTINE,
and in the ISLETS OF LANGERHANS in the PANCREAS.
Other endocrine cells form organized and independent
structures, such as the ADRENAL GLANDS
that cap the KIDNEYS and the THYROID GLAND which
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lies across the front of the THROAT. Each endocrine
structure produces specific hormones. Collectively
the endocrine structures function in intimate synchronization
and interaction with each other,
continuously adjusting their secretions to accommodate
the ever-changing conditions and needs
of the body. An intricate matrix of cascades and
feedback mechanisms allows this dynamic coordination
to initiate and inhibit cellular activity.
Endocrine Structure
ADRENAL GLANDS
adrenal cortex
adrenal medulla
gastrointestinal tract
HYPOTHALAMUS
THE MAJOR ENDOCRINE STRUCTURES
AND THEIR HORMONES
Primary Hormones
ALDOSTERONE
CORTISOL
DEHYDROEPIANDROSTERONE (DHEA)
DOPAMINE
EPINEPHRINE
NOREPINEPHRINE
cholecystokinin (CCK)
enterogastrone
gastric inhibitive polypeptide (GPI)
gastrin
motilin
secretin
SOMATOSTATIN
vasoactive intestinal peptide (VIP)
ANTIDIURETIC HORMONE (ADH)
CORTICOTROPIN-RELEASING HORMONE
(CRH)