Organization of the Endocrine System

Barrett EJ. Organization of the endocrine system. In Boron WF, Boulpaep EL, eds. Medical Physiology A Cellular and Molecular Approach. New York Saunders 2003. 

The endocrine system also functions to regulate and control physiological processes of the body. However, the endocrine system accomplishes its functions by sending out chemical signals called hormones into the blood. Glands, the organs of the endocrine system, se-... 

Endocrine Effects. No information was available that reported the effects of formaldehyde on the endocrine system of humans after inhalation, oral, or dermal exposure. Formaldehyde has been reported not to exert adverse effects on organs of the endocrine system in laboratory animals and, hence, is not a major target organ for formaldehyde toxicity after inhalation (Appelman et al. 1988 Kamata et al. 1997 Kems et al. 1983b Maronpot et al. 1986 Monticello et al. 1989 Woutersen et al. 1987) or oral (Johannsen et al. 1986 Til et al. 1988b, 1989 Tobe et al. 1989 Vargova et al. 1993) exposure. No data regarding endocrine effects in animals after dermal exposure were located. 

The organization of the endocrine system can best be described in relation to the central nervous system. Three levels of endocrine tissues can be distinguished on the basis of their association with the central nervous system (Figure 30-12). The first level consists of those that are (or were) derived from nerve cells these include the hypothalamus, adrenal medulla, thyroid C-cell, and gastrointestinal enterochromaffin cells. The hypothalamus and adrenal medulla still retain their neural connections and can therefore be regarded as endocrine extensions of the nervous system. The C-cell and the gut cells, however, are APUD cells and lack neural connections. These four tissues produce hormonal peptides or amines having, like neurotransmitters, rapid-onset, short-term effects. 

Investigations of genetically controlled polymorphisms of various organs of the endocrine system have recently begun. At the present time, numerous examples of ge-... 

Pesticides have a statistically reliable effect on children in zones where OCPs are intensively used (in the Salyansk region of Azerbaijan, the amount of OCPs introduced into humans exceeded public health standards by up to 7.7 times). Primary illness of the endocrine system increased 3.1 times in children up to age 15 (over a five year observation period) in disruptions in diet and metabolism, the nervous system, and the sensory and respiratory organs in increased frequency of illness (over five years) in children up to age 15 (an overall increase by 3.6 times, and by class of illness, from 2.2-7.6 times) in the prevalence of pathological disruptions according to data from medical examinations of children from 8-14 years (an overall increase by 2.3 times, and by class of illness by 2.0-8.4 times) in... 

The endocrine system is an anatomically diverse assemblage of organs, united by the common fnnetion of secreting hormones. Organs, with qnite different fnnetions, inclnding the kidney, liver and intestine, also secrete hormones and, in this sense, they too are part of the endocrine system. In a functional sense, the endocrine system also inclndes the blood which transports hormones to their target cells, tissues or organs. 

Different chemicals provide communication between tissues/organs of the reproductive system. They are classified into three groups steroids, peptides and fatty messengers. They can also be classified as endocrine or local hormones, some of which are discussed in Chapter 12. 

Although it is the dominant organ of the neural system, the brain also has an endocrine function, enabling the all-important overlap between neural and endocrine control systems. The most obvious and classically recognized hormonal function of the brain arises from the peptide hormones of the hypothalamus. The hypothalamus is intimately connected with the pituitary, producing the hypothalamic-pituitary axis. The hypothalamus is part of the brain the pituitary, although located within the skull, is not part of the brain but is part of the endocrine system. Peptide hormones from the hypothalamus influence pituitary function and thus endocrine function throughout the body. 

Figure 5.2 The Hypothalamic Pituitary Axis The hypothalamus is part of the diencephalon within the brain. The pituitary, although located within the skull, is more correctly a part of the endocrine system than the nervous system. Together, the hypothalamus and pituitary form the interface between the nervous system and endocrine system and exert control over the majority of other hormone secreting organs. Releasing and inhibiting factors permit the hypothalamus to control the pituitary. Pituitary hormones are released into the general circulation, affecting metabolic function throughout the thorax and abdomen.

Endocrine disrupting chemicals Exogenous chemicals that alter functions) of the endocrine system and consequently cause adverse health effects in an intact organism, its progeny or (sub)populations. 

Xenobiotics can adversely affect the normal functions of the cells/organs of the reproductive system. These agents may induce a variety of outcomes, including prevention of ovulation and impairment of ovum transport, fertilization, or implantation. Endocrine disruptors may mimic endogenous hormones as well as directly destroy cellular components, leading to cell death. More indirect effects may include inhibition of key enzymes involved in steroid synthesis. 

Pineal gland A tiny, light-sensitive organ in the center of the brain, also called the pineal eye or "third eye." In reptiles it controls changes in skin color. In humans it is a master gland of the endocrine system, probably regulating many biorhythms. 

One study that overcomes some of the shortcomings of those just cited reported adverse neurodevelopment outcomes following maternal exposures to 19 organic solvents and mixtures of these. 13 In this study, the women were occupationally exposed to the chemicals listed in Table 24.3. Also included in this table are the K, values and whether or not the specific chemical is a known teratogen or a known endocrine disruptor. 5 It is interesting to note that only three of the chemicals in the study—ethanol, trichloroethylene, and mineral spirits (a mixture of hydrocarbon solvents)—are endocrine disruptors. This shows that teratogenic effects can be induced by chemicals and mixtures that are independent of the endocrine system. 

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