Describe a hormone as a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs

A hormone is a chemical substance produced by specialized glands in the endocrine system, which are secreted directly into the bloodstream. Hormones serve as messenger molecules that travel throughout the body to target specific organs or tissues, altering their activity and regulating various physiological processes.

Key Characteristics of Hormones

• Production: Hormones are synthesized by endocrine glands such as the pituitary gland, thyroid gland, adrenal glands, pancreas, and gonads (ovaries and testes) .
• Transport: Once produced, hormones enter the bloodstream, where they are carried to distant target organs. Some hormones circulate freely in the blood, while others bind to transport proteins that help regulate their availability and activity .
• Target Specificity: Hormones exert their effects on specific target cells that possess receptors for that hormone. This interaction follows a “lock-and-key” mechanism, where only cells with the appropriate receptors respond to the hormone’s presence .

Functions of Hormones

Hormones play vital roles in numerous bodily functions, including:

• Metabolism Regulation: Hormones like insulin and glucagon regulate blood sugar levels and energy metabolism.
• Growth and Development: Growth hormone influences growth in children and adolescents.
• Reproductive Functions: Sex hormones (e.g., estrogen, testosterone) regulate reproductive processes and secondary sexual characteristics.
• Homeostasis Maintenance: Hormones help maintain homeostasis by regulating blood pressure, fluid balance, and electrolyte levels