Endocrine hormones

True endocrine hormones, however, remain a fairly well defined group. Virtually all of the hormones used therapeutically (discussed below) fit into this grouping. Examples include insulin, glucagon, GH and the gonadotrophins. 

Once released from the cell of origin, the signal ligand must travel to its site of action. For the classical endocrine hormones this means via the bloodstream. Given that blood plasma is approximately 94% water, the physical nature of the hormone is important. Peptides are hydrophilic and so circulate unbound to any other molecule whereas... 

Not the least of the factors for consideration in evaluating a possible risk pertains to the characteristics of those persons exposed. A hazard does not become an actuality until there is a risk of human exposure. Consequently, in evaluating the risk, you must take into account those who are or might be exposed, not only in terms of numbers but also in relation to the realities of individual variation and predisposition. These considerations can be difficult in a political environment that demands equality. However, it should be recognized that not all persons are equal either in their predisposition towards an adverse response to a toxic assault or in the severity of their response to that assault. Differences in response can occur, for example, by reason of age, sex, and physical fitness. A classic example exists in the manufacture and processing of female endocrine hormones in which a woman, and particularly a pregnant woman, may be more at risk than a man under the same circumstances. Less dramatic, but... 

Type III neurotransmitters These are peptides (neuropeptides), and most are considered to be neuromodulators rather than neurotransmitters. As a further complication, some of these are also found in the intestine, where they act as local hormones or even endocrine hormones (Chapter 4 Table 14.1). 

The classification of vitamin D as a vitamin is largely an historical accident. It conforms much more to the definition of a hormone it is produced in one part of the body and released into the blood to affect other parts of the body in this case, a novel endocrine hormone (Chapter 12). 

Figure 17.20 Cytokines produced by activated Th cells and some of their effects. The cytokines produced have several functions activation of B-cells, macrophages and cytotoxic T-cells. The cytokines, along with endocrine hormones, stimulate responses in the whole body (e.g. lipolysis in adipose tissue, protein degradation in muscle, acute phase protein production in liver. Chapter 18).

In the ebb phase, there is increased activity of the sympathetic nervous system and increased plasma levels of adrenaline and glucocorticoids but a decreased level of insulin. This results in mobilisation of glycogen in the liver and triacylglycerol in adipose tissue, so that the levels of two major fuels in the blood, glucose and long-chain fatty acids, are increased. This is, effectively, the stress response to trauma. These changes continue and are extended into the flow phase as the immune cells are activated and secrete the proinflammatory cytokines that further stimulate the mobilisation of fuel stores (Table 18.2). Thus the sequence is trauma increased endocrine hormone levels increased immune response increased levels of cytokines metabolic responses. 

Table 18.2 Endocrine hormones and cytokines responsible for metabolic changes in trauma...

Initially the level of insulin decreases, favouring increased rates of lipolysis, fatty acid oxidation, muscle protein degradation, glycogenolysis and gluconeogenesis. It soon increases, however, as a result of insulin resistance, when the stimulation of the above processes will depend on the cytokine levels. For details of endocrine hormone effects, see Chapter 12. For details of cytokines see Chapter 17. 

Hormones are chemical signaling substances. They are synthesized in specialized cells that are often associated to form endocrine glands. Hormones are released into the blood and transported with the blood to their effector organs. In the organs, the hormones carry out physiological and biochemical regulatory functions. In contrast to endocrine hormones, tissue hormones are only active in the immediate vicinity of the cells that secrete them. 

Connected to the brain by a stalk (Fig. 30-1), the pituitary gland releases at least ten peptide or protein hormones that regulate the activity of other endocrine (hormone-producing) glands in distant parts of the body. The pituitary is composed of several distinct parts the anterior lobe (adenohypophysis), a thin intermediate portion (pars intermedia), and a posterior lobe (neurohypophysis). Each has its own characteristic endocrine functions. 

FIGURE 28-1 Negative feedback control in the hypothalamic-pituitary-endocrine pathways. Excitatory and inhibitory effects are indicated by (+] and H, respectively. Negative feedback loops occur owing to inhibition of the endocrine hormone on the pituitary and hypothalamus. 

The primary purpose of the endocrine system is to maintain homeostasis — that is, to maintain a relatively constant internal environment in the face of a constantly changing external environment. The endocrine system consists of hormones and the glands and tissues that produce the hormones. A hormone is a chemical substance released by certain cells to effect the function of other distant cells (endocrine function). Many compounds act as endocrine hormones as well as having paracrine and autocrine functions. Paracrine and autocrine describe actions on nearby cells and on other cells that produce the substance, respectively. There is considerable overlap between substances classified as hormones and other chemical messengers such as neurotransmitters and cytokines. Many substances function in more than one of these categories. For example, epinephrine and norepinephrine function as both neurotransmitters and adrenal medullary hormones. 

The hypothalamus-pituitary, thyroid, parathyroid, pancreas, adrenals, ovary, and testes are considered to be the principal endocrine glands producing hormones. A more complete list of the major endocrine hormones and their primary gland of origin is shown in Table 9.1. 

As indicated in Table 9.1, the endocrine hormones can be divided into two major chemical classes (1) the peptides and amino acid derivatives and (2) the cholesterol-based steroid compounds. In general, the former are believed to interact primarily with membrane-associated receptors, while the latter are more lipophilic and are able to gain entrance into target cells. In any event, overactive or underactive endocrine... 

The nose and its associated structures responsible for our sense of smell linking our nervous and endocrine (hormonal) systems serves to make our perception and reactions to an odour a unique experience. This reinforces its significance in the psychosomatic (mind-body) interchange. Scent can affect mood and emotion at a deep level. People often find that scents are powerfully effective in provoking long-forgotten memories. 

Cushing s syndrome (hypercorticism) is an endocrine hormone disorder caused by high levels of cortisol in the blood. Cushing s disease refers to one specific cause, a non-cancerous tumour (adenoma) in the pituitary gland that produces a large amount of ACTH, which in turn elevates cortisol. It can usually be cured by surgery. 

Plants not only evolved allelochemicals with broad activities (see Section 1.3.1) but also some that can interfere vdth a particular target [3,6,17-19,25]. Targets that are present in animals but not in plants are nerve cells, neuronal signal transduction, and the endocrinal hormone system. Compounds that interfere with these targets are usually not toxic for the plants producing them. Plants have had to develop special precautions (compartmentation resin ducts, trichomes, laticifers) in order to store the allelochemicals with broad activities that could also harm the producer. 

A (natural or synthetic) chemical that causes changes in endocrine (hormonal) function, leading to adverse effects in an animal or its offspring, enzymes... 

---