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positive feedback endocrine system

At the moment of onset of the glucose infusion, the pancreatic B cells are either removed from the system or left itact. 25. Thrasher TN, Keenan CR, Ramsay DJ. ENDOCRINE CELLS AS RECEPTORS AND EFFECTORS The pubertal growth spurt lasts 2 to 3 years, and it is accompanied by the appearance of secondary sexual characteristics. Lambertz SW, Macleod RM. The effects of estradiol are complex. In the amount of time from the 10th to the 20th week of pregnancy, the fetus grows 12.7 cm (5 inches) in length. and progesterone, which stimulates the growth of the egg-producing Neuropeptide Y stimulates food intake in satiated animals and, over the long term, causes obesity. CHAPTER 5 FEEDBACK CONTROL IN ENDOCRINE SYSTEMS (ACTH, adrenocorticotropin hormone; CRH, corticotropin-releasing hormone; pit., pituitary.) which stimulates sperm production. Insulin secretion, however, is just one of a set of autonomically mediated responses that occurs to the sight, smell, or taste of food. In these disorders, known as multiple endocrine neoplasia (MEN), affected patients have germ line mutations (heritable mutations that are incorporated into all of the cells of the body) in genes that predispose them to endocrine gland hyperplasia (an abnormal increase in the number of cells in the gland) and tumour development. Dampney RA. The pubertal growth spurt is associated with both an increase in nocturnal secretion of growth hormone and an increase in serum concentrations of sex steroids. The major endocrine systems are regulated by negative feedback, a process believed to maintain hormonal levels within a relatively narrow range. Such performance requires a means to determine the level of activity or the concentration of the variable that is regulated. The hypothalamus secretes neurohormones that stimulate (or inhibit) the secretion of specific anterior pituitary hormones, which in turn stimulate a peripheral target gland to secrete hormone and, with sufficient stimulation, to grow (see Chap. The quantitative relations among system components in engineering and the mathematical description of these have been useful in describing biologic control systems.1 The notion of a setpoint reference signal, which can be explicitly delineated in an engineered system, is, in most biologic systems, an apparent setpoint, deduced by the behavior of the system, and probably normally arises from the interaction of a hormone or metabolite with receptors and cellular function. Thus, the overall performance of a relatively slow system may appear tighter than anticipated and more like that of a system with an overall fast-time constant. ( Log Out /  Moreover, many hormones are bound in the circulation by high-affinity specific binding globulins. Vitale ML, Chiocchio SR. Serotonin, a neurotransmitter involved in the regulation of luteinizing hormone release. Axons containing neuropeptide Y, in turn, innervate nearby hypothalamic cell groups that are known to constitute a neural network that determines food intake. Potentiation of hormonal responses to hemorrhage and fasting, but not hypoglycemia in conscious adrenalectomized rats. Corticosterone inhibition of ACTH secretion. The diagram shows the (hypothetical) blood glucose (top) and insulin (bottom) concentrations before and during infusion of glucose. 19. Production of thyrotropin, luteinizing hormone, and follicle-stimulating hormone by nonpituitary tumours does not occur. 16). Control strategies in physiological systems. responses bring about all the familiar feelings: the ball Hyponatremia can occur as a result of vasopressin (antidiuretic hormone) secretion, usually by small-cell carcinomas of the lung, and hypoglycemia may be caused by tumour production of insulin-like growth factors or, very rarely, insulin. A fall in plasma sodium concentration is reflected in the sodium concentration in the tubular ultrafiltrate. Rapid growth occurs during infancy and then slows until the onset of puberty, when it increases strikingly for several years. Plant TM. Endocrine tissue may modify its hormonal secretory rate as a regulated variable changes but may not actually sense the change itself. Endocr Rev 1984; 5:1. Ultrashort-loop feedback is suspected to occur when a hormone acts on its own cell type to inhibit further secretion of itself. 5-8). Role of arginine vasopressin in regulation of systemic arterial blood pressure. How does this happen? The ovaries (and testes) make and release estradiol (and testosterone) How and why your heart pounds when you are scared or nervous Neural control of somatotropic function. Cardiovascular response to stress. The increased concentration of insulin causes increased glucose transport into those cells that contain insulin receptors and a reduction in blood glucose concentration. 12 and Chap. There is evidence suggesting that this feedback can occur either by inhibiting the secretion of growth hormone-releasing hormone or by stimulating the secretion of growth hormone-inhibiting hormone (somatostatin) into the hypophysial portal circulation.6,7 There is growing evidence that similar short-loop feedback circuits exist for the other hypophysial hormones. FIGURE 5-2. Evans JJ. However, in cases in which the tumour cannot be removed or its function reduced, adrenalectomy (removal of the adrenal glands) or treatment with a drug such as ketoconazole, an antifungal drug that inhibits adrenal steroid synthesis, may be more effective. LH stimulates testosterone secretion in men and ovulation, luteal formation, and estrogen and progesterone secretion in women. 206). reactions that mobilize glucose and fatty acids, Cellular energy reserves are increased and your muscles The cycle is interrupted when suckling stops (see Chap. The gonadal endocrine system has been best studied from this point of view. PARTURITION AND SUCKLING to stop releasing testosterone). ULTRASHORT-LOOP FEEDBACK (Redrawn from Guyton AC. A variable is monitored by a receptor that is sensitive to changes in that variable. Multisystem control involves specialized receptor organs that are directly connected to or embedded in central components of the autonomic nervous system. ovarian follicle and prepares the uterus for pregnancy. One key difference is that positive feedback loops are used to eradicate a stimulus. Am J Physiol 1984; 246:F533. Because the ovum-containing follicle was the … CHAPTER REFERENCES.

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