Hormone remote

Iodine is essential in the mammalian diet to produce the thyroid hormone thyroxine deficiency in humans causes goitre. Collectively, deficiencies of iodine, iron, zinc and vitamin A in humans are thought to be at least as widespread and debilitating as calorie deficiencies (Welch and Graham, 1999). The main source of iodine in soils is oceanic salts rather than parent rock, and so deficiency is most widespread in areas remote from the sea (Fuge, 1996). In principle deficiency is easily corrected with dairy supplements. However in practice this is not always feasible. Addition of iodate to irrigation water has successfully corrected widespread iodine deficiency in parts of China where the usual methods of supplementation had failed (Cao et al., 1994 Jiang et al 1997). However there is not much information on the behaviour of iodine in soil and water systems. 

Lipophilic groups that are not easily hydrolyzed are used extensively for depot preparations, which liberate the active drug molecule slowly, for a period of days or weeks. Steroid hormone palmitates and pamoates, and antimalarial esters (e.g., cycloguanil pamoate, 3.29), can deliver the active drugs over a prolonged time cycloguanil, for example, is released over a period of several months. This can he a great convenience for the patient, especially in areas with remote medical facilities. 

In endocrine signaling the hormone is synthesized in specific signaling, or endocrine, cells and exported via exocytosis into the extracellular medium (e.g. blood or lymphatic fluid in animals). The hormone is then distributed throughout the entire body via the circulatory system so that remote regions of an organism can be reached. 

Malignancies, particularly of neural crest origin, are known to affect brain function adversely through remote (presumably hormonal) effects on neural tissue. For example, ovarian adenocarcinoma can selectively induce a profound cerebellar syndrome caused by the selective death of Purkinje cells (presumably from a neurotoxic hormonal factor). Such phenomena simply illustrate the complicated nature of CNS functioning and the need to be cautious about explanations in the absence of systematic data. 

The effects of plant hormones are quite complex, one plant hormone often having a wide range of effects. However, the various phenomena observed when a plant hormone is applied do not always establish that the plant hormone is directly causing the effect in untreated plants. Some effects of a plant hormone may be direct while others are indirect, with the site of action being quite remote from the location of the end effect. Additionally, there is evidence for rather complex interactions among the various plant hormones. 

Hormones usually stimulate metabolic activities in tissues remote from the secretory organ. They are active at exceedingly low concentrations, too. Furthermore, most hormones are metabolized rapidly, so their effects are often short-lived, allowing rapid adaptations to metabolic changes. 

Endocrine hormones are produced by endocrine glands and specialised neurosecretory cells of the hypothalamus. They are released into the bloodstream and transported to remote sites in the body to exert their activity (Fig. 6.1). 

Phytohorntones, plant hormones The classic P. are endogenous regulators of plant growth and development. They are analogous to animal hormones in that the sites of their synthesis may be remote from the sites of their action, but in contrast to animal hormones, P. have multiple activities and low action specificities. Oligosaccbarins (see), however, are much more specific and are elective at concentrations similar to those at which animal hormones are effective (10- -10" M), but they may not be transported from their site of synthesis to the site of their action. 

It is now firmly established that the synthesis and release of the hormones of the adenohypophysis are controlled by substances released from nerve endings in the hypothalamus and conveyed to the anterior pituitary gland via the portal vessels. The evidence which demonstrated the fundamental importance of the hypothalamus and the hypothalamo-hypophysial portal vessels came mainly from experiments which involved transection of the pituitary stalk, transplantation of the pituitary gland to a site remote from the sella turcica or electrical stimulation of the hypothalamus. 

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