Hormones: Living Messengers

Hormones are chemical substances that our bodies use to regulate every physiological process. They are secreted by one cell or organ and used by another. They circulate in our blood from the secretory organ to the target organ. They are regulated by complex feedback loops that keep them balanced within specific ranges. They are necessary for growth, reproduction, maintenance of homeostasis, metabolism and all other life functions.

Regulation: Feedback Loops

Some hormones are regulated by a feedback loop that involves special trophic hormones which cause the release of other hormones.

Thyroid hormone, for instance, which controls metabolic processes, is kept within a narrow range. The hypothalamus produces thyroid releasing factor, which stimulates the pituitary to release thyroid stimulating hormone, which stimulates the thyroid gland to release more thyroid hormone. Thyroid releasing factor (TRF) and thyroid stimulating hormone (TSH) are both trophins.

If too much thyroid hormone is circulating in the bloodstream, the hypothalamus senses this and shuts off the production of thyroid releasing factor. The pituitary doesn't release thyroid stimulating hormone, and the level of thyroid hormone drops. If it gets too low, that causes the hypothalamus to release TRF again.

Cellular Functions And Receptors

Hormones function by regulating processes within the individual cells in our bodies. They do this by combining with receptors on the cell membrane. The hormone "fits" into a specific receptor much the same way a key fits into a lock. When the hormone combines with a receptor, it causes or blocks some activity.

For example, when insulin combines with insulin receptors, glucose is carried into the cell, where it can be used for energy.

Their Building Blocks

Hormones are made from other substances, primarily proteins and fats. There are three main types of hormones.

Amine-derived hormones are made from tryptophan and tyrosine, two amino acids. Catecholamines are amine-derived hormones.

Peptides are made from chains of amino acids. Insulin is a peptide hormone. Sometimes peptid chains have glucose molecules attached to them, and they are called glycoproteins. These are larger hormone molecules, such as follicle stimulating hormone.

Lipid or phospholipids are made from fatty acids. Steroids, including sex hormones, and prostaglandins are examples of lipid hormones.

Hormone Replacement Therapy

Because they are necessary for cellular function, inadequate levels of any hormone can have serious effects. Many of the diseases of aging may be due to problems with hormone production, transportation or receptors. Replacing them when you are deficient is often necessary, especially as people grow older. Many people take thyroid hormone or other hormone replacements.