Term	Definition	Prefix	Root	Suffix
Acromegaly	Enlargement of the extremities		acro	megaly
Adenoma	Tumor of a gland		aden	oma
Adenomalacia	Softening of a gland		aden/o	malacia
Adrenalectomy	Removal of the adrenal gland		adrenal	ectomy
Endocrine	To secrete inside	endo	crine
Hyperglycemia	Too much sugar in the blood	hyper	glyc	emia
Pancreatitis	Inflammation of the pancreas		pancreat	itis
Polyphagia	Excessive hunger	poly	phagia
Polyuria	Excessive excretion of urine	poly	uria
Thyroidectomy	Removal of the thyroid		thyroid	ectomy

^*A transition syllable or vowel may be added to or deleted from the word parts to make the combining form.

Abbreviations of the Endocrine System

Abbreviation	Meaning
ADH	Antidiuretic hormone
ANS	Autonomic nervous system
BMR	Basal metabolic rate
DM	Diabetes mellitus
FSH	Follicle stimulating hormone
GH	Growth hormone
SIADH	Syndrome of inappropriate antidiuretic hormone
STH	Somatotropic hormone
TH	Thyroid hormone
TSH	Thyroid-stimulating hormone

Structure and Function of the Endocrine System

The primary function of the endocrine system is to produce hormones that monitor and coordinate body activities (Fig. 18-1). Hormones are chemical messengers secreted by the endocrine glands. Each type of hormone moves through the blood to its own target cells, which react specifically to it. The endocrine glands secrete hormones directly into the bloodstream. Hormones may be proteins, glycoproteins, polypeptides, amino-acid derivatives, or lipids.

FIGURE 18-1 The endocrine system. (From Patton KT, Thibodeau GA: *Anatomy & physiology,* ed 7, St. Louis, 2010, Mosby.)

Hormones may be divided into two classes on the basis of their composition and the way they influence their target organs:

Nonsteroid hormones are proteins that work as “first-messengers.” They act on cells of the target organ to cause them to produce or release a second messenger molecule.

Steroid hormones influence the target organ independently.

Hormones may also be divided into categories on the basis of their function:

Tropic hormones target other endocrine structures to increase their growth and secretions.

Sex hormones influence reproductive changes.

Anabolic hormones stimulate the process of building tissues.

Hormones direct many body processes, including growth, metabolism, and reproductive functions (Table 18-1). Hormones regulate the body’s reaction to stress and maintain the internal environment (homeostasis). The importance of hormones in the body can be demonstrated by the numerous and diverse disorders that occur when the amount of hormone produced is either too great (hypersecretion) or too little (hyposecretion). The quantity of hormones in the blood is monitored through a negative feedback mechanism, which stimulates more secretion when needed (Fig. 18-2). Additionally, the autonomic nervous system controls and stimulates the secretion of the hormones of the adrenal gland.

TABLE 18-1

Endocrine Glands and Hormones *

Gland	Hormone	Function
Pituitary	Somatotropin (or growth hormone [GH])	Promotes tissue growth and development
Pineal	Melatonin	Supports the biological clock
Thyroid	Thyroxine (TH)	Regulates the metabolic rate
Parathyroid	Parathyroid hormone (PTH)	Regulates calcium and phosphates in the bloodstream and bones
Thymus	Thymosin	Stimulates development of T cells
Adrenal	Epinephrine	Regulates autonomic nervous system response
Pancreatic islets	Insulin	Regulates blood sugar
Ovaries	Estrogen	Regulates female sexual characteristics
Testes	Testosterone	Regulates male sexual characteristics