Environmental Endocrine - Health - Lecture Slides, Slides of Public Health

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Environmental Endocrine Disruptors Part I: Toxicity Ovaries (women)Testicles (men) Pancreas Adrenal glands Hypothalamus Thyroid gland Parathyroidgland Pineal gland Pituitary gland docsity.com Course Objectives  Be familiar with the terms used, especially those pertaining to environmental endocrine disruption.  Undertake a brief review of the human endocrine system, which regulates our body’s day-to-day function and development.  Understand the basic modes of endocrine disruption. Appreciate the potential, yet at times even dreadful, effects of endocrine disruption. docsity.com Endocrine System (II)  The glands that make up the (human’s) endocrine system are hypothalamus, pituitary, thyroid, parathyroid, adrenals, pineal body, pancreas, ovaries, and testicles.  The primary function of these glands is to synthesize and secrete hormones. Acting as body’s messengers, hormones transfer information and instructions from one set of cells to another; the shape of each hormone molecule is specific and can bind to certain cellular receptors only. docsity.com Types of Hormones  Hormones are typically grouped into three classes: steroids, amines, and peptides.  Nearly all the steroid hormones are lipids synthesized from cholesterol; they are responsible for the development of many male and female sex characteristics. Amine hormones are (all) derived from the amino acid tyrosine secreted by the thyroid. Most hormones are peptides, thus each with only a short chain of amino acids; they are synthesized largely as proteins first. docsity.com Hypothalamus, Pituitary  The hypothalamus is located below the thalamus, in the lower center part of the brain; beneath this gland is the pituitary, which has the size of a pea. Together, these two glands control many other endocrine functions.  Hormones from the two glands are crucial to pregnancy, birth, lactation, and a woman’s menstrual cycle, including ovulation.  Growth hormone and antidiuretic hormone are also crucial hormones secreted by the anterior and posterior pituitary, respectively. docsity.com Ovaries, Testicles  The female ovaries and the male testicles, responsible for many sex characteristics, are referred to as the gonad glands or sex organs.  Female ovaries synthesize the hormones estrogen and progesterone in varying amounts depending on where in her cycle a woman is.  Testicular production of the sex hormone testosterone (a principle androgen) begins during fetal development, continues for a short time after birth, nearly ceases during childhood, and then resumes at puberty. docsity.com Modes of Disruption (I)  There are two basic avenues of endocrine disruption, each of which involves primarily two modes of biochemical reactions. One avenue is on the function or the structure of the glands or the target cells, directly or not.  The other avenue is on the metabolism and the function of hormones that the endocrine glands secrete or that the target cells bind to.  In all cases, the disruption can lead to either an excessive activation or an excessive inhibition of a hormone’s normal function. docsity.com Modes of Disruption (II)  The endocrine glands as a target organ can be impaired or affected directly or indirectly through certain toxicologic disruptions.  For example, their hormone secretion can be impaired by an intruder’s ability to inhibit the biosynthesis or the secretion process.  Other examples include the secondary endocrine toxicity of DES on the ovary and of testosterone secretion, and the primary toxicity of nicotine on the adrenal, nitrogen on the ovary, and estrogens on the pituitary. docsity.com Pesticides as EEDs (II)  Pesticides identified as environmental endocrine disruptors (EEDs) with estrogenic effects include: DDT, dieldrin, endosulfan, fenvalerate, kepone, lindane, methoxychlor, permethrin, triadimefon, and triadimenol.  Pesticide EEDs considered as androgenic or antiandrogenic are: atrazine, p,p’-DDE, lindane, procymidone, vinclozolin, etc.  Those affecting the reproductive system are fewer, including: ketoconazole, oxy- chlordane, tributyltin, and trifluraline. docsity.com Literature Evidence (I) Many in vitro assays are currently used in U.S. EPA’s mandated Endocrine Disruptor Screening Program; these assays are used as the first tiered test to identify and confirm the potential of hundreds (or perhaps thousands) of chemicals as endocrine disruptors.  There are also sufficient in vivo studies showing that many chemicals are capable of inducing endocrine disruption, even at very low doses comparable to background levels in people living in many places. docsity.com Literature Evidence (II)  Field observations in wildlife over the years reveal a worrying trend of endocrine disruption affecting their population growth.  From 1970s to 1980s, a great number of herring gulls and other fish-eating birds were noted to have deformities caused by exposure to dioxin released into the Great Lakes. More astounding is the observation in the 1980s that male alligators in Lake Apopka had testosterone levels as low as a female’s and penises 25% smaller than the normal males’. docsity.com