Endocrine glands adrenals

Endocrine glands Adrenal weight decreased in females and increased in males Reduced weight of thyroid... 

Endocrine glands Adrenals weight i , f Thyroid weight i... 

Adrenal gland weights were not affected in rats treated by gavage with 1,500 mg/kg/day trichloroethylene in com oil for 14 days (Berman et al. 1995). Histopathological changes in endocrine glands (thyroid, parathyroid, pancreas, adrenals, pituitary) have not been observed in rats or mice exposed by gavage to trichloroethylene in oil for intermediate or chronic durations (Maltoni et al. 1986 NCI 1976 NIP 1988, 1990). 

No histopathological changes in endocrine tissues (adrenal glands and thyroid) were noted in rabbits receiving <480 mg/kg/day Cellulube 220 for < 14 days (Carpenter et al. 1959), or in rats receiving <350 mg/kg/day tributyl phosphate for 18 weeks (Laham et al. 1985). 

Steroid hormones are produced by the adrenal cortex, testes, ovaries, and placenta. Synthesized from cholesterol, these hormones are lipid soluble therefore, they cross cell membranes readily and bind to receptors found intracellularly. However, because their lipid solubility renders them insoluble in blood, these hormones are transported in the blood bound to proteins. Furthermore, steroid hormones are not typically preformed and stored for future use within the endocrine gland. Because they are lipid soluble, they could diffuse out of the cells and physiological regulation of their release would not be possible. Finally, steroid hormones are absorbed easily by the gastrointestinal tract and therefore may be administered orally. 

A trophic hormone acts on another endocrine gland to stimulate secretion of its hormone. For example, thyrotropin, or thyroid-stimulating hormone (TSH), stimulates the secretion of thyroid hormones. Adrenocorticotropin, or adrenocorticotropic hormone (ACTH), stimulates the adrenal cortex to secrete the hormone cortisol. Both trophic hormones are produced by the pituitary gland in fact, many trophic hormones are secreted by the pituitary. The pituitary gland is sometimes referred to as the "master gland" because its hormones regulate the activity of other endocrine glands. 

Adrenal gland A triangle-shaped organ positioned at the top of the kidney which functions as a double endocrine gland . The larger outer adrenal cortex secretes three classes of steroid hormones glucocorticoids (e.g., cortisol), minerlocorticoids (aldosterone) and small amounts of sex steroids (e.g., testosterone). The inner adrenal medulla secretes catecholamines (e.g., adrenaline and noradrenaline). 

Named after Thomas Addison who first described the clinical condition in the mid 1850s, Addison s disease is one of the commonest endocrinopathies. At one time, most cases of Addison s were due to infection, usually by tuberculosis, of the adrenal cortex but nowadays the likely cause is autoimmune destruction of the tissue, and may be associated with dysfunction of other endocrine glands. 

Nerve impulses stimulate the hypothalamus to send specific hormones to the pituitary gland, thus stimulating (or inhibiting) the release of tropic hormones. The anterior pituitary hormones in turn stimulate other endocrine glands (thyroid, adrenals, pancreas) to secrete their characteristic hormones, which in turn stimulate specific target tissues. 

Location of major endocrine glands in humans. The hypothalamus regulates the anterior pituitary, which regulates the hormonal secretions of the thyroid, adrenals, and gonads (ovary in the female and testis in the male). 

In the studies of long-term exposure of rats to both triphenyltin hydroxide and bis(tributyltin)oxide, most of the tumors were found in endocrine glands. In addition to the pituitary adenomas associated with bis(tributyltin)oxide and triphenyltin hydroxide, there was also an increased incidence of pheochromocytomas of the adrenal gland, parathyroid carcinomas and pancreatic adenocarcinomas in animals from at least one sex. Triphenyltin hydroxide was associated with an increased incidence of testicular Leydig cell tumors in male rats at the highest dose. Hepatic tumors were found in male and female mice following 80 weeks of triphenyltin hydroxide administration. 

Figure 18.3. Endocrine-immune inter-relationship in depression. In depression, the hypothalamic-pituitary-adrenal (HPA) axis is up-regulated with a down-regulation of its negative feedback controls. Corticotrophin releasing factor (CRF) is hypersecreted from the hypothalamus and induces the release of adrenocortico-trophic hormone (ACTH) from the pituitary. ACTH interacts with receptors on adrenocortical cells and cortisol is released from the adrenal glands adrenal hypertrophy can also occur. Release of cortisol into the circulation has a number of effects, including elevation of blood glucose. The negative feedback of cortisol to the hypothalamus, pituitary and immune system is impaired. This leads to continual activation of the HPA axis and excess cortisol release. Cortisol receptors become desensitized leading to increased activity of the pro-inflammatory immune mediators and disturbances in neurotransmitter transmission.

Nicotine is highly addictive and is a CNS stimulant and depressant. Ingestion of nicotine results in an almost immediate kick, because it causes a discharge of epinephrine from the adrenal cortex. This stimulates the CNS and other endocrine glands, which causes a sudden release of glucose. Stimulation is then followed by depression and fatigue, leading the user to seek more nicotine. Nicotine is... 

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. 

Figure 13.1 Major human endocrine glands (1) pineal gland, (2) pituitary gland, (3) thyroid gland, (4) thymus, (5) adrenal gland, (6) pancreas, (7) ovary and (8) testes.

Many other important steroids are hormones secreted by the endocrine glands. Two important classes are the sex hormones and the adrenal cortical steroids. 

There are several approaches to the study of metabolism. First, isolation of steroid metabolites from various steroid-forming tissues (testes, ovaries, placentae, adrenal glands) makes it possible to evaluate the usefulness of a particular endocrine gland in the production of steroids. Secondly, in vitro experiments are conducted by incubation with tissue preparations followed by isolation of the metabolities of steroids. Thirdly, in vivo experiments are carried out by isolation of steroids from biological fluids, mainly from animal and human blood and urine. This last method includes evaluation of the rates of secretion and metabolism of... 

LDH (M.W. 134,000) oceurs as five tetrameric isoenzymes composed of two different types of subunits. Subunits M (for muscle) and H (for heart) are encoded by loci in chromosomes 11 and 12, respectively. Two subunits used in the formation of a tetramer yield five combinations H4(LDH-1), H3M(LDH-2), H2M2(LDH-3), HM3(LDH-4), and M4(LDH-5). The tissue distributiont of LDH isoenzymes is variable. For example, LDH-1 and LDH-2 are the principal isoenzymes in heart, kidney, brain, and erythrocytes LDH-3 and LDH-4 predominate in endocrine glands (e.g., thyroid, adrenal, pancreas), lymph nodes, thymus, spleen, leukocytes, platelets, and nongravid uterine muscle and LDH-4 and LDH-5 preponderate in liver and skeletal muscle. In tissue injury or insult, the appropriate tissue isoenzymes appear in plasma (Chapter 8) thus, determination of LDH isoenzyme composition has diagnostic value. 

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