Endocrine system pituitary

Unit IX discusses drugp that affect the endocrine system and consists of five chapters antidiabetic drugs, pituitary and andrenocortical hormones, thyroid and antitliyroid drag s, male and female hormones, and dragp acting on the uterus. 

Imura, H and Fukata, J., Endocrine-paracrine interaction in communication between the immune and endocrine systems. Activation of the hypothalamic-pituitary-adrenal axis in inflammation. Eur. J. Endocrinol. 130,32-37 (1994). 

Vasopressin (antidiuretic hormone) is a peptide synthesized in the hypothalamus and secreted from the neurohypophysis of the pituitary gland. This substance plays an important role in the long-term regulation of blood pressure through its action on the kidney to increase reabsorption of water. The major stimulus for release of vasopressin is an increase in plasma osmolarity. The resulting reabsorption of water dilutes the plasma toward its normal value of 290 mOsM. This activity is discussed in more detail in Chapter 10 (the endocrine system) and Chapter 19 (the renal system). 

Reports of the effects of Li+ upon the thyroid gland and its associated hormones are the most abundant of those concerned with the endocrine system. Li+ inhibits thyroid hormone release, leading to reduced levels of circulating hormone, in both psychiatric patients and healthy controls [178]. In consequence of this, a negative feedback mechanism increases the production of pituitary TSH. Li+ also causes an increase in hypothalamic thyroid-releasing hormone (TRH), probably by inhibiting its re-... 

GHRF and GHRIF are peptides secreted by hypothalamic neurons termed neuroendocrine transducers (the name is apt, as these interface between the nervous and endocrine systems). The factors that regulate their secretion are poorly understood but probably involve both nerve impulses originating from within the brain and feedback mechanisms, possibly involving pituitary hormones. 

The endocrine system is composed of hormone-producing organs within the body. Probably the most important endocrine organ is the pituitary gland, located at the base of the skull and intimately associated with the hypothalamus, both the pituitary and the hypothalamus secrete a wide variety of peptidic hormones and are crucial to the... 

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.

Anterior lobe of pituitary is the master gland of the endocrine system as a whole because it produces peptide trophic hormones which affect the other ductless/endocrine glands. The anterior lobe secretes the following hormones ... 

The control of metabolism, growth, and reproduction is mediated by a combination of neural and endocrine systems located in the hypothalamus and pituitary gland. The pituitary weighs about 0.6 g and rests at the base of the brain in the bony sella turcica near the optic chiasm and the cavernous sinuses. The pituitary consists of an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis) (Figure 37-1). It is connected to the overlying hypothalamus... 

There are also a few examples of positive feedback mechanisms in the endocrine system.25 43 In a positive feedback loop, rising concentrations of one hormone cause an increase in other hormones, which, in turn, facilitates increased production of the first hormone. The primary example of this type of feedback occurs in the female reproductive system, where low levels of estrogen production increase the release of pituitary hormones (LH, FSH).10 43 Increased LH and FSH then facilitate further estrogen production, which further increases pituitary hormone secretion, and so on (see Chapter 30). Positive feedback mechanisms are relatively rare, however, compared with negative feedback controls in the endocrine system. 

Use of Hormones to Alter Normal Endocrine Function. Because of the intrinsic control mechanisms in the endocrine system, administration of exogenous hormones can often affect the normal release of hormones. This fact can be exploited in certain situations to cause a desired change in normal endocrine function. For instance, oral contraceptives containing estrogen and progesterone inhibit ovulation by inhibiting the release of LH and FSH from the anterior pituitary. 

Thyroid hormone release is subject to the negative feedback strategy that is typical of endocrine systems controlled by the hypothalamic-pituitary axis. Increased circulating levels of the thyroid hormones (T4, T3) serve to limit their own production by inhibiting TRH release from the hypothalamus and TSH release from the anterior pituitary.30,35 This negative feedback control prevents peripheral levels of thyroid hormones from becoming excessively high. 

The SD rat is a commonly used laboratory animal. However, it has limitations when used to evaluate the effects of chemicals on the endocrine system, including the pituitary and mammary gland, because of a high spontaneous tumor incidence in these organs. At about 9-12 months of age, the SD rat begins to experience prolonged periods... 

Endocrine Effects. Little is known about the effects of aluminum on endocrine systems. The oral administration of sodium aluminum phosphate to male and female Beagle dogs for 6 months did not alter thyroid, adrenal, or pituitary gland weight or microanatomy (Katz et al. 1984 Pettersen et al. 1990). These organs were also normal in male and female Wistar rats fed a diet containing unspecified amounts of aluminum phosphide/ammonium carbamate for 24 months (Hackenberg 1972). 

Hierarchical control and feedback control, both positive and negative, are a fundamental feature of endocrine systems (Figure 13.2). Each of the major hypothalamic-pituitary-hormone axes is governed by negative feedback ... 

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