Endocrine tissue

W. W. Douglas, J. Nagasawa, and R. Schulz in H. Heller and K. Lederis, eds., Subcellular Organisation andFunction in Endocrine Tissues, University Press, Cambridge, Mass., 1971, pp. 353—377. 

Measurement of contaminants in fish has concentrated on muscle tissue since the aim has generally been to protect the health of the consumer rather than that of the fish. Endocrine tissue such as the gonads has been much more rarely examined, while data for adrenal, thyroid and pituitary levels are virtually non-existent. More data are available for the liver, as a lipid rich tissue and the major site of xenobiotic catabolism, but the concentrations have rarely been related to its capacity to produce vitellogenin or metabolise endogenous hormones. Tissue concentrations of a wide range of chemicals, are at a level which suggests that, either alone or in combination, they will cause significant endocrine disruption in fish in many polluted habitats. 

Pituitary. The primary endocrine gland that controls many of the endocrine tissues of the body. The pituitary is in turn con-... 

Excitability refers to the capacity of nerves and other tissues (e.g. cardiac), as well as individual cells, to generate and sometimes propagate action potentials, signals that serve to control intracellular processes, such as muscle contraction or hormone secretion, and to allow for long- and short-distance communication within the organism. Examples of excitable cells and tissues include neurons, muscle and endocrine tissues. Examples of nonexcitable cells and tissues include blood cells, most epithelial and connective tissues. 

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). 

Gastrin is a hormone produced by gastric endocrine tissue — specifically, the G cells in the pyloric gland area. It is released into the blood and carried back to the stomach. The major function of gastrin is to enhance acid secretion by directly stimulating parietal cells (HC1) and chief cells (pepsinogen). Gastrin also stimulates the local release of histamine from enterochromaf-fin-like cells in the wall of the stomach. Histamine stimulates parietal cells to release HC1. 

Lloyd, R.V., Jin, L., and Fields, K. (1990) Detection of chromogranins A and B in endocrine tissues with radioactive and biotinylated oligonucleotide probes. Am. I. Surg. Pathol. 14, 35-43. 

Chronic pancreatitis (CP) is a syndrome of destructive and inflammatory conditions resulting from long-standing pancreatic injury. It is characterized by irreversible fibrosis and destruction of exocrine and endocrine tissue but is not invariably progressive. 

Endocrine Effects. Histopathological examination of endocrine tissues (thyroid, parathyroid, adrenals, pituitary, pancreas) after intermediate-duration inhalation exposure revealed no treatment-related lesions in male Sprague-Dawley rats exposed to 500 ppm n-hexane daily for 6 months, 22 hours a day (IRDC 1981) or in Fischer 344 rats of both sexes exposed to up to 10,000 ppm for 6 hours a day,... 

These hormones are essential for the maintenance of pregnancy. The only natural progestin hormone, progesterone (3.38), is produced by the corpus luteum, an endocrine tissue formed in the ovary by the ruptured ovarian follicle after the level of luteinizing hormone peaks. If pregnancy occurs, the corpus luteum persists for the first three months of the pregnancy after that, its role is taken over by the placenta as the major... 

Fig. 3.5. Endocrine, paracrine and autocrine signal transduction, a) endocrine signal transduction the hormone is formed in the specialized endocrine tissue, released into the extracellular medium and transported via the circulatory system to the target cells, b) paracrine signal transduction the hormone reaches the target cell, which is found in close juxtaposition to the hormone producing cell, via diffusion, c) autocrine signal transduction the hormone acts on the same ceU type as the one in which it is produced.

Fig. 4.11. Principle of signal transduction by RXR heterodimers. The activated hormone can be made available to the RXR heterodimer in three different ways, a) The hormone (e.g. T3 hormone) is synthesized in endocrinal tissue and reaches the DNA-bound RXR-T3R heterodimer in the nucleus via passive transport, b) The active hormone is formed in the cytosol from an inactive apo-hormone (as for, e.g. 9-ds-retinoic add), c) The hormone is synthesized intracellularly. In aU three cases, the binding of the hormone-RXR-heterodimeric complex is the signal that induces transcription activation of the downstream genes. After Mangelsdorf and Evans, 1995.

Steroid Hormones The steroid hormones (adrenocortical hormones and sex hormones) are synthesized from cholesterol in several endocrine tissues. 

FIGURE 23-11 Cascade of hormone release following central nervous system input to the hypothalamus. In each endocrine tissue along the pathway, a stimulus from the level above is received, amplified, and transduced into the release of the next hormone in the cascade. The cascade is sensitive to regulation at several levels through feedback inhibition by the ultimate hormone. The product therefore regulates its own production, as in feedback inhibition of biosynthetic pathways within a single cell. 

FIGURE 23-24 The endocrine system of the pancreas. In addition to the exocrine cells (see Fig. 18—3b), which secrete digestive enzymes in the form of zymogens, the pancreas contains endocrine tissue, the islets of Langerhans. The islets contain a, /3, and S cells (also known as A, B, and D cells, respectively), each cell type secreting a specific polypeptide hormone. 

Fifth, certain kallikreins, such as human kallikrein 6, are highly expressed in the central nervous system. It has previously been shown that hK6, and possibly some other kallikreins, are implicated in inflammatory reactions within the central nervous system that lead to demyelination. The association of hK6 and some other kallikreins with AD and multiple sclerosis points to the possibility that some of these enzymes may play important roles within the central nervous system. In addition, many of these enzymes have been found in endocrine tissues such as the islets of Langerhans, thyroid, pituitary, and others, pointing to the possibility that they may participate in prohormone or hormone processing. 

VMAT1 Endocrine tissue Sympathetic ganglia Enterochromaffin cells Monoamines (Km low pM range) Monoamine analogues Toxins (e.g. MPP+) Reserpine (Ki 34 nM) Psychostimulantia (e.g. Amphetamine, cocaine)... 

The similarities between ecdysone synthesis in the insect prothoracic gland and the ovary are obvious and in each case synthesis is initiated in response to a hormone originating in the brain. Both bear a striking resemblance to the mammalian system where steroid hormone synthesis in the various endocrine tissues is initiated in response to the release of appropriate hormones from the anterior pituitary. 

Q13 The pancreas produces hormones in areas of endocrine tissue the islets of Langerhans. The major hormones are insulin, from the beta-cells (/0-cells), and glucagon, from alpha-cells (a-cells). Delta cells produce somatostatin. 

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