The Endocrine System
The Endocrine System
The entirety of an organism’s hormone secreting cells is called the endocrine system and organs that secrete hormones are called endocrine glands. There are over 50 known hormones in the human body that regulate a range of functions such as sexual maturation to the control of one’s blood sugar levels. The endocrine glands include the hypothalamus, pituitary, thyroid, parathyroid, pineal, adrenal, thymus, pancreas, ovaries, and testes. These glands release hormones into the bloodstream, or in some cases into the cell, which then bind to cellular receptors. The biological action of hormones is due to changes in various cellular characteristics and processes that are triggered by hormone binding to specific receptors. These biological responses can be varied, such as changes in cell membrane ion permeability or gene transcription.
Much of our knowledge about endocrine disruption is based on studies of growth, development, and reproduction. These processes are regulated by steroid and thyroid hormones that can be affected by many environmental chemicals. One of the more common mechanisms of endocrine disruption occurs when the chemical mimicks a steroid hormone’s effect by binding to the receptor for that hormone. A chemical that has this mechanism of action is termed an agonist. Other EDCs may be hormone antagonists, where their binding to hormone receptors reduces hormone activity by preventing the endogenous hormone from binding to that receptor and producing the intended cellular response.
Endocrine disrupting chemicals may also act by indirect mechanisms, by interfering with hormone synthesis, degradation, or transport. For example there are many enzymes that are responsible for hormone catabolism. Some EDCs may induce an up regulation of these enzymes leading to increased catabolism and subsequently reduced hormone levels. Many hormones that circulate in the blood are actually bound to plasma proteins; some EDCs bind to these proteins and displace the hormone. The end result is an increase in blood hormone clearance and a decrease in circulating hormone levels.
Much of our knowledge about endocrine disruption is based on studies of growth, development, and reproduction. These processes are regulated by steroid and thyroid hormones that can be affected by many environmental chemicals. One of the more common mechanisms of endocrine disruption occurs when the chemical mimicks a steroid hormone’s effect by binding to the receptor for that hormone. A chemical that has this mechanism of action is termed an agonist. Other EDCs may be hormone antagonists, where their binding to hormone receptors reduces hormone activity by preventing the endogenous hormone from binding to that receptor and producing the intended cellular response.
Endocrine disrupting chemicals may also act by indirect mechanisms, by interfering with hormone synthesis, degradation, or transport. For example there are many enzymes that are responsible for hormone catabolism. Some EDCs may induce an up regulation of these enzymes leading to increased catabolism and subsequently reduced hormone levels. Many hormones that circulate in the blood are actually bound to plasma proteins; some EDCs bind to these proteins and displace the hormone. The end result is an increase in blood hormone clearance and a decrease in circulating hormone levels.