Endocrine system Hormones

The ability of certain metals to bind to estrogen receptor a suggests that these metals can increase the risk of disorders of the endocrine system (hormonal system, endocrine). Long exposure of women to lead and mercury can lead, among other things, to infertility, miscarriage, and premature delivery. 

Endocrine System Hormones Signals and Communication between Cells and Tissues... 

In its broadest sense, environmental chemistry might be considered to include the chemistry of everything outside of the synthetic chemist s flask The moment that a chemical substance is released to the environment, its physico-chemical properties may have an enormous impact on ecological systems, including humans. Researchers have identified 51 synthetic chemicals that disrupt the endocrine system. Hormone disrupters include some of the 209 polychlorinated biphenyls (PCBs), and some of the 75 dioxins and 135 furans that have a myriad of documented effects (1). The latter half of the twentieth century has witnessed more synthetic chemical production than any other period in world history. Between 1940 and 1982, the production of synthetic chemicals increased about 350 times. Billions of pounds of synthetic materials were released into the environment during this period. United States production of carbon-based synthetic chemicals topped 435 billion pounds in 1992 or 1600 pounds per capita (2). 

Leukotrienes and Prostanoids. Arachidonic acid (AA) (213) and its metabohtes are iavolved ia cellular regulatory processes ia all three principal chemical signaling systems endocrine (see Hormones), immune, and neuronal (62). FoUowiag receptor activation or iacreased iatraceUular... 

Interaction of vitamin D and its metaboUtes with sex hormones has been demonstrated, particularly ia birds ia which the egg-laying functions combine calcium needs and reproductive activity. The metaboUtes of vitamin D behave as hormones. As such, they play an active role ia the endocrine system, along with other hormones, to maintain the various body functions. Several biological influences of metaboUtes of vitamin D have been studied, including effects related to cancer (193—197), skin diseases (198—201), immunomodulatory effects (202,203), and Alzheimer s disease (204—206) (Fig. 9). 

Figure 1 A schematic diagram of the endocrine system of fish. TRH = thyrotrophin releasing hormone GnRH = gonadotrophin releasing hormone CRH = corticotrophin releasing hormone TSH = thyroid stimulating hormone GtH = gonadotrophins I and II ...

The liver plays an important role in the endocrine system. The concentrations of hormones in plasma, and the activity of the glands which secrete them, are determined by the rate at which they are deactivated by the liver. The liver also has a major function in female reproduction since it is the target tissue of ovarian estrogen, to which it responds by producing the yolk protein vitellogenin. " Xenobiotics that affect either of these functions can therefore be considered to be potential endocrine disrupters. 

Among vertebrate species, the neuro-endocrine-immime system is responsible for many complex, inter-related physiological processes including neuronal, homeostatic, reproductive and immune functions. There are four main types of hormone polypeptides, eicosanoids, steroids and thyroid hormones. Reflecting the inter-dependency of the neiiro-endocrine and immune systems, hormones, neuropeptides and other neiirotransmitters are known to be produced by some immune cells and play a role in the regulation of the immune system, while endocrine and nervous tissues express receptors for many substances produced by the immune system. The major focus of interest in endocrine disruption has... 

Unit IX discusses drugp that affect the endocrine system and consists of five chapters antidiabetic drugs, pituitary and andrenocortical hormones, thyroid and antitliyroid drag s, male and female hormones, and dragp acting on the uterus. 

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine system because of the abihty of these chemicals to mimic or block endogenous hormones, or otherwise interfere with the normal function of the endocrine system. Chemicals with this type of activity are most commonly referred to as endocrine disruptors. Some scientists believe that chemicals with the ability to disrupt the endocrine system are a potential threat to the health of humans, aquatic animals, and wildlife. Others believe that endocrine disrupting chemicals do not pose a significant health risk, particularly in light of the fact that hormone mimics exist in the natural environment. Examples of natural hormone mimics are the isoflavinoid phytoestrogens (Adlercreutz 1995 Livingston 1978 Mayr et al. 1992). 

Vertebrates share many functional similarities in their endocrine systems, including their regulatory control and the nature of the hormones and their receptors (Munkittrick et al. 1998). The reproductive abnormalities observed in wildlife populations may therefore potentially be extrapolated to effects in the reproductive health of human populations, if similar exposures to EDCs occur. 

THE DIVERSITY OF THE ENDOCRINE SYSTEM / 437 Table 42-4. General features of hormone classes. 

Much of the material on individual endocrine glands present in the twenty-fifth edition has been replaced with new chapters dealing with the diversity of the endocrine system, with molecular mechanisms of hormone action, and with signal transduction. 

---