Endocrine System
Define 10 terms relating to the endocrine system.
Describe the function of the endocrine system.
Identify at least nine endocrine system structures.
Identify at least one hormone produced by each of the 10 endocrine glands.
Describe at least three methods used to assess the function of the endocrine system.
Basal metabolic rate (BAY-sal met-uh-BOL-ik rayt) Minimal energy expended for respiration, circulation, peristalsis, muscle tone, body temperature, and glandular activity of the body at rest
Hormone (HORE-mone) Chemical substance produced in the body that has specific regulatory effect on the activity of a specific organ
Immunoassay (im-yoo-no-AS-say) Quantitative determination of antigenic substances by examination of blood
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| 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.
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.
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.
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 |
*Most of the endocrine glands secrete more than one hormone with functions not listed here.
Glands and their Hormones
Hypothalamus
The hypothalamus is a structure located above the pituitary gland that translates nervous system impulses into endocrine system messages. It regulates the secretions of the pituitary adenohypophysis by secreting neurohormones that stimulate or inhibit pituitary hormones. For example, the hypothalamus produces a growth hormone–releasing hormone that stimulates the pituitary to release growth hormone.
Pituitary
The pituitary gland (hypophysis) is sometimes called the “master” gland because the hormones that it produces regulate the secretion of other glands (Fig. 18-3). It is located at the base of the brain and is divided into two parts: the anterior and posterior.
Brain Byte
Although the pituitary gland is called the “master” gland because its hormones control other glands, the hypothalamus releases chemicals that stimulate the release of pituitary hormones.
The anterior pituitary (adenohypophysis) gland produces seven hormones:
Thyroid-stimulating hormone (TSH) stimulates the growth and secretion of the thyroid gland.
Adrenocorticotrophic hormone (ACTH) stimulates the growth and secretion of the adrenal cortex.
Follicle-stimulating hormone (FSH) stimulates the growth of the ovarian follicle, production of estrogen in females, and production of sperm in males.
Luteinizing hormone (LH) stimulates ovulation and the formation of the corpus luteum in the menstrual cycle.
In males the LH, called interstitial cell-stimulating hormone, stimulates the secretion of testosterone.
Lactogenic hormone (prolactin) stimulates the secretion of milk and influences maternal behavior.
Somatotropic hormone, also called the growth hormone, accelerates the growth of the body.
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