The endocrine system

Differentiate between the primary functions of the nervous system and the endocrine system

• Describe biochemical and functional distinctions among steroid hormones, protein/peptide hormones, and amine hormones

• Explain beneficial effects of the binding of hormones to plasma proteins

• Distinguish between a trophic and a nontrophic hormone • Describe the three types of hormone interactions • Explain the two primary mechanisms by which hormones carry out

their effects • Describe how the effects of hormones are amplified • Describe how the pituitary gland is formed during embryonic devel-

opment • Describe anatomical and functional relationships between the hypo-

thalamus and the pituitary gland • Explain how negative feedback mechanisms limit release of hor-

mones from the adenohypophysis • List functions and describe mechanisms regulating release of hor-

mones from the neurohypophysis • List functions and describe mechanisms regulating release of hor-

mones from the adenohypophysis • Discuss functions and factors regulating release of the following hor-

mones: thyroid hormones, calcitonin, parathyroid hormone, catecholamines, aldosterone, cortisol, adrenal androgens, insulin, and glucagon

Two major regulatory systems make important contributions to homeostasis: the nervous system and the endocrine system. In order to maintain relatively

constant conditions in the internal environment of the body, each of these systems influences the activity of all the other organ systems. The nervous system coordinates fast, precise responses, such as muscle contraction. Electrical impulses generated by this system are very rapid and of short duration (milliseconds). The endocrine system regulates metabolic activity within the cells of organs and tissues. In contrast to the nervous system, this system coordinates activities that require longer duration (hours, days) rather than speed. Examples of such activities include growth; long-term regulation of blood pressure; and coordination of menstrual cycles in females. The endocrine system carries out its effects through the production of

hormones

, chemical messengers that exert a regulatory effect on the cells of the body. Secreted from

endocrine glands

, which are ductless structures, hormones are released directly into the blood. They are then transported by the circulation to the tissues upon which they exert their effects. Because they travel in the blood, the serum concentrations of hormones are very low (10

to 10

M

); therefore, these molecules must be very potent.