Facts on File Encyclopedia of Health and Medicine

Structures of the Endocrine System
HYPOTHALAMUS THYMUS
PITUITARY GLAND ISLETS OFLANGERHANS
anterior pituitary lobe ADRENAL GLANDS
posterior pituitary lobe adrenal cortex
PINEAL GLAND adrenal medulla
THYROID GLAND OVARIES(female)
PARATHYROID GLANDS 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 hor-
mones. The endocrine glands release their hor-
mones 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 STOMACHand SMALL INTESTINE,
and in the ISLETS OFLANGERHANSin the PANCREAS.
Other endocrine cells form organized and inde-
pendent structures, such as the ADRENAL GLANDS
that cap the KIDNEYSand the THYROID GLANDwhich

lies across the front of the THROAT. Each endocrine

structure produces specific hormones. Collectively

the endocrine structures function in intimate syn-

chronization and interaction with each other,

continuously adjusting their secretions to accom-

modate the ever-changing conditions and needs

of the body. An intricate matrix of cascades and

feedback mechanisms allows this dynamic coordi-

nation to initiate and inhibit cellular activity.

THE MAJOR ENDOCRINE STRUCTURES

AND THEIR HORMONES

Endocrine Structure Primary Hormones

ADRENAL GLANDS

adrenal cortex ALDOSTERONE

CORTISOL

DEHYDROEPIANDROSTERONE(DHEA)

adrenal medulla DOPAMINE

EPINEPHRINE

NOREPINEPHRINE

gastrointestinal tract cholecystokinin (CCK)

enterogastrone

gastric inhibitive polypeptide (GPI)

gastrin

motilin

secretin

SOMATOSTATIN

vasoactive intestinal peptide (VIP)

HYPOTHALAMUS ANTIDIURETIC HORMONE(ADH)

CORTICOTROPIN-RELEASING HORMONE

(CRH)

96

THE ENDOCRINE SYSTEM

The endocrine glands produce hormones, chemical messengers that regulate many functions within the body. Physi-
cian 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.