Hormone

The chemical structure of the hormone Epinephrine (adrenaline)

Hormones represent the chemical messengers of the endocrine system, playing an integral role in the body's internal regulation in conjunction with the nervous system. Found in every multicellular organism, hormones interact with specific cells that possess the corresponding receptors for each hormone.

Hormonal Function and Production

Cells capable of hormone production exist throughout the body, with specialized cells congregating in glands, dedicated to hormone synthesis and release. Hormones can originate from different types of glands - "endocrine" glands, which secrete hormones directly into the bloodstream, and "exocrine" glands, which release their products externally through ducts, as seen in sweat and salivary glands.

The concept of hormones was established in 1902 with the discovery of secretin. The term 'hormone', however, was not introduced until 1905.

Hormonal Activities

Hormones enact a broad spectrum of activities, from regulating metabolism and instigating cell growth and death, to triggering sexual development, as evidenced by the roles of estrogen and progesterone in female puberty. They also assist in maintaining homeostasis, a stable internal state, managing factors like temperature, hydration, and blood sugar levels. A hormone released from one gland may even stimulate other glands to produce different hormones.

Categories of Hormones

Hormones in vertebrates generally fall into four categories, based on their chemical composition:

• Steroid hormones: Derived from cholesterol, they include sex hormones like estradiol and testosterone, and the stress hormone, cortisol.
• Eicosanoids: These are lipid-based hormones, synthesized from fats. Eicosanoids predominantly function as local hormones, transmitting messages in close proximity to their production site.
• Amino acid-derived hormones: This group includes hormones such as melatonin, which affects the brain, and thyroxine, which has a broad cellular reach. Many neurotransmitters, or hormones passed between nerve cells, belong to this category.
• Peptides, polypeptides, and proteins: These hormones range from small peptides like TRH and vasopressin, to larger proteins, like insulin and growth hormone. Complex protein hormones with carbohydrate side-chains are known as glycoprotein hormones, with luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone serving as examples.

Hormonal Regulation

Hormonal regulation, the control of hormone production and release, is an essential aspect of biology.

Negative Feedback

Most hormonal regulation operates via a negative feedback system. In this setup, a hormone induces an effect, which is then detected by the hormone-producing cells. Upon recognizing the impact of the hormone, these cells halt its production. This regulatory feedback loop ensures that hormone levels in the body remain balanced and effectively maintain homeostasis.

Hormonal Impact on Health

Alterations in hormone levels can lead to various health conditions. Overproduction or underproduction of specific hormones can disrupt the body's normal function and lead to disorders such as diabetes, thyroid diseases, growth disorders, and many others. Consequently, understanding the regulation and function of hormones is vital for diagnosing and treating these conditions.

See Also

• Endocrine system
• Endocrine gland
• Exocrine gland
• Steroid hormones
• Eicosanoids
• Amino acid-derived hormones
• Peptide hormones
• Glycoprotein hormones

Hormone Resources
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