Section 1

Hormones

• Hormones are chemical messengers secreted by cells that act to regulate the activity of other cells.

• Hormones have many functions, including regulation of growth; maintenance of homeostasis; and regulation of energy production, use, and storage.

• Ductless glands called endocrine glands make most of the body's hormones. Specialized cells in the brain, stomach, and other organs also make and release hormones. Exocrine glands secrete nonhormonal chemicals into specific body locations.

• Amino acid-based hormones bind to cell-membrane receptors of their target cells, activating a second messenger that then activates or deactivates enzymes in a cascade fashion.

• Steroid and thyroid hormones bind to receptors inside the cell. The hormone-receptor complex binds to DNA in the nucleus and turns genes either on or off.

• Similar to hormones, neuropeptides and prostaglandins act on nearby cells to regulate cellular activities.

Vocabulary hormone (p. 1031) endocrine gland (p. 1031) endocrine system (p. 1031)

exocrine gland (p. 1031) amino acid-based hormone (p. 1031)

steroid hormone (p. 1031) target cell (p.1032) receptor (p.1032)

second messenger (p. 1032) neuropeptide (p. 1033) prostaglandin (p. 1033)

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