Hormones act as chemical messengers, controlling many basic functions, such as growth, development, reproduction, how food is utilised in the body, blood pressure, blood glucose levels and fluid balance. Examples of hormones are insulin from the pancreas, which controls blood glucose, and the sex hormones, oestrogen from the ovary and testosterone from the testicles, which affect reproductive function.
Hormones are carried in the blood stream to distant target organs or cells where they perform particular functions. Examples are the pituitary hormone from the brain which causes the ovary to release an egg, or the hormones from the adrenal gland which prepare the body to face stress. Other hormones are released within an organ or tissue – a collection of cells related by their functions – and act locally within the organ or tissue, such as preventing an egg maturing in the ovary.
The endocrine system also includes a third group of hormones called ‘neurohormones’ which are released by nerve cells either locally or into the blood stream where they act further away. More...
The following animation illustrates how the glands of the endocrine system are distributed in the human body. To find out more point your mouse to the glands in the image.
1.2 What is the definition of endocrine disruptors?
Endocrine disruption is not, in itself, a measure of toxicity – the occurrence of adverse health effects. Rather, it is considered to be a change that may lead to harmful effects. For example, a potential endocrine disruptor (pED) is a foreign substance or mixture that possesses properties that might be expected to lead to endocrine changes in an individual life form, in its offspring, or in populations.
Please note that there is no widely accepted list of endocrine disruptors or potential endocrine disruptors and that the IPCS document summarised here does not provide such list. The European Commission is developing a candidate list of substances in order to set priorities for further evaluation of their role in endocrine disruption (COM(2001) 262 final)
The following animation illustrates only one of the ways in which EDCs can act. Click the play button to start the animation
1.3 Why is there concern about endocrine disruptors?
Recent years have seen growing concern among scientists and the public at large about endocrine disrupting chemicals (EDCs) that may interfere with the endocrine system and cause harmful effects.
The presence of EDCs in our environment raises concerns because:
harmful effects have been observed on reproduction, growth and development in some species of wildlife, both aquatic and terrestrial,
there are increases in some human reproductive disorders and some cancers which could be related to disturbance of the endocrine system, and
adverse effects from some environmental chemicals known to act on the endocrine system have been observed in laboratory animals.
This has provoked many national and international organizations, as well as scientific and public interest groups, to initiate research programmes, conferences, workshops and expert panels to address and evaluate EDC-related issues. More...