16 Oct positive feedback endocrine system
World Rev Nutr Diet 1986; 47:163. RECEPTORS THAT CAN INITIATE MULTISYSTEM RESPONSES Figure 5-2 shows a theoretical situation in which the control of glucose is examined. hormone: a chemical that is made by specialist cells, usually within an endocrine gland. 106). The dotted arrows show the sites of feedback by cortisol.
Neurons in the hypothalamus release somatostatin and growth hormone-releasing hormone (GHRH) into the circulation that bathe the growth hormone-secreting cell (somatotrope). J Appl Physiol 1995; 78:2025. Aldosterone facilitates sodium reabsorption from the distal tubules, which leads to an increase in plasma sodium.
FIGURE 5-8.
Physiol Rev 1987; 67:962. Chapter References. The corticotropin-release inhibitory factor hypothesis: a review of the evidence for the existence of inhibitory as well as stimulatory hypophysiotropic regulation of adrenocorticotropin secretion and biosynthesis. 183). Long-loop feedback occurs in most of the anterior pituitary hormone systems and is most apparent when the capacity for hormone synthesis or secretion in the peripheral target gland is compromised or abolished. The metabolism of hormones after their secretion also serves as a mechanism of hormone regulation and may result in either an increase or a decrease in hormone activity. All of these variables are regulated by the feedback arrangement described earlier (see Fig. 17. A decrease in sodium delivery to the distal tubule is sensed by the macula densa cells. Production of thyrotropin, luteinizing hormone, and follicle-stimulating hormone by nonpituitary tumours does not occur. Corticosteroids and the control of function in the hypothalamic-pituitary-adrenal (HPA) axis. 5-7; see Chap. This causes the ovaries Some blood-borne agents (nonhormonal) have profound effects on the secretion of certain endocrine gland cells. The central nervous system processes and integrates afferent information from the mechano-receptors. If the error signal is positive, the effector gland is stimulated to secrete, and the concentration of hormone in the circulation increases to levels that are adequate to effect the normalization of the perturbed regulated variable.
10. The initiation of a stimulus to CRH until a rise in circulating concentration of cortisol or corticosterone occurs requires <5 minutes. The pubertal growth spurt lasts 2 to 3 years, and it is accompanied by the appearance of secondary sexual characteristics. A good example of a positive feedback system involves oxytocin and its other effect: causing contraction of uterine muscle during childbirth (Figure 1.28). There is little evidence for this phenomenon; however, it could be of considerable importance in the regulation of secretion of posterior pituitary hormones. Treatment ordinarily involves surgical removal or drug-induced destruction of the tumour.
Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. Am J Physiol 1999; 277:R795. Am J Physiol 1984; 246:F533.
In response to the perturbation, the endocrine system adjusts the amount of “free” circulating hormone in an attempt to regain homeostasis. The endocrine system consists of ductless glands that secrete hormones into the blood stream.
25. When an internal or external stimulus perturbs a regulated variable, neural or endocrine responses (or both) occur that counteract the disturbance and return the variable to within its normal range.
Angiotensin II, by way of an action on the subfornical organ, also stimulates the conscious desire to drink fluids and further augment sympathetic activity.19,26 Moreover, angiotensin II acts on the adrenal glomerulosal cells to stimulate the secretion of aldosterone,27 which causes increased reabsorption of sodium by the kidney and aids in the restoration of the extracellular fluid volume. The gonadotropin-releasing hormone (GnRH) is released in bursts that appear to drive secretion of luteinizing hormone (LH) in episodes (see Chap. or exercising is a good example of the endocrine system producing The sense organ can be a modified structure that is (a) connected to the central nervous system, (b) connected to the gland, or (c) an integral part of the endocrine effector cell. ( Log Out / Ann NY Acad Sci 1994; 746:22. response to stimuli outside of your body, releases hormones Cardiovascular afferent signals and drinking in response to hypotension in dogs. Endocr Rev 1992; 13:387. In both of these examples, there is a neuroendocrine control loop. In Multiple endocrine deficiency disorders result in multiple hormonal deficiencies and are suspected to be caused by underlying heritable genetic mutations. Notice that for the same stimulus, the feedback system with the fast-time constant regulates the variable near normal levels and does not overshoot or under-shoot as does the feedback system with the slow-time constant. 8,Chap.
30.
to complete. How and why your heart pounds when you are scared or nervous Release of oxytocin and vasopressin by magnocellular nuclei in vitro: specific facilitatory effects of oxytocin on its own release. In a multicomponent feedback system, the component with the slowest time constant determines the delay time between stimulus and response (time constant of the system). blood and lowering the amounts found in the blood. Viewing the ventromedial hypothalamus from the adrenal gland. Any change in the variable is sensed, and a response (hormone) is elicited to bring the variable back within its “normal” range. As part I definitely enjoying every little bit of it I have you bookmarked to check out new stuff you post…, I have bookmarked you contactos con mujeres , this is excelent information my friends, nicely done contactos con mujeres. flight!
Gonadal regulation of hypothalamic gonadotropin-releasing hormone release in primates.
Vitale ML, Chiocchio SR. Serotonin, a neurotransmitter involved in the regulation of luteinizing hormone release. Denef C. Paracrine interactions in the anterior pituitary.
14). The effector organ can be an endocrine gland (adrenal cortex, pancreas) or an autonomic postganglionic nerve terminal. Recurrent inhibition of antidromically identified rat supraoptic neurons.
Similarly, the production of steroid or thyroid hormones by tumours of tissues that do not normally produce these hormones does not occur.
A constant supply of most hormones is essential for health, and sustained increases or decreases in hormone production often lead to disease. another feedback cycle. Evidence suggests that this arises from synchronous bursts of activity in hypothalamic neurons that secrete the appropriate releasing factors. Still slower, in hours, are the effects of steroid and thyroid hormones, which are mediated by alterations in the rate of gene transcription and translation, and of protein synthesis. FIGURE 5-1. Keller-Wood ME, Dallman MF. There also are several genetic disorders characterized by hormone-producing tumours of several endocrine glands. The steady-state glucose concentration would be determined by the volume into which glucose is distributed and the rate at which glucose is lost from that volume of distribution in the absence of insulin. The direct feedback effects of cortisol, the other steroid hormones, and thyroid hormones on their trophic hormonal controllers allow tighter control of these systems. ( Log Out /
However, growth hormone has an effect on the hypothalamic-releasing and release-inhibiting hormones that regulate its secretion (Fig. How does this happen? In females, LH and FSH tell the ovaries to secrete estradiol This is a function of the time constant of each component of the feedback loop. For example, bone age is delayed in children with growth hormone deficiency and accelerated in children with growth hormone-producing tumours. Negative feedback control operates widely throughout the body at the molecular (e.g., end-product inhibition of enzyme activity), cellular, and whole systems/body level. 95). Human endocrine system - Human endocrine system - Feedback regulation mechanisms of endocrine signaling: A constant supply of most hormones is essential for health, and sustained increases or decreases in hormone production often lead to disease. that responds to temperature changes by telling a furnace to
Darlington DN, Jones RO, Marzella L, Gann DS. The minimum time required for cortisol to increase gluconeogenesis, enabling increased hepatic glucose secretion, may be ~2 hours.
The receptor is connected to a structure or structures that process and integrate the signal generated by alterations in the variable. The atrophic adrenal cortex does not secrete normal quantities of cortisol, and the abrupt discontinuation of exogenous glucocorticoids may lead to a patient who displays all the signs of cortisol deficiency (see Chap.
Long- and short-loop feedback. One of the most clinically obvious and simplest forms of negative feedback control in endocrine systems involves suppression of the secretion of a trophic factor (or hormone) by the hormone it stimulates. Functional organization of central pathways regulating the cardiovascular system.
Glucose concentration in the open-loop condition increases well above the normal range; whereas under closed-loop control, glucose concentration is maintained close to the normal range. At the moment of onset of the glucose infusion, the pancreatic B cells are either removed from the system or left itact. The action of glucose on the pancreatic B cell was mentioned earlier. Darlington DN, Keil LC, Dallman MF. Clearly, the action of insulin reduces the stimulus to its secretion. 85), a continual bidirectional flow of information—one relaying the conditions in the organism, and the other directing neural and endocrine responses—is present and functions to maintain appropriate operating conditions. Examples of conditions that affect sex chromosomes, and hence growth and development, include Klinefelter syndrome (47,XXY, 48,XXYY, 48,XXXY, 49,XXXYY, and 49,XXXXY), Turner syndrome (45,X, 46,XX, 45,X, and 47,XXX), and hermaphroditism (46,XX). Endocr Rev 1993; 14:480. Houk JC. 79 and Chap. 1. Textbook of medical physiology, 9th ed. HYPOTHALAMIC–PITUITARY–TARGET ENDOCRINE FEEDBACK These X-rays reveal the extent of maturation of the epiphyses (growth centres) of bones, which allows the bone age of the child being examined to be compared with the bone age of healthy children of the same chronological age. Am J Physiol 1984; 246:R1. However, the administration of these same blocking agents or blockade of the sympathetic nervous system seriously impairs the restitution of arterial pressure after hemorrhage.30 Peptide and protein hormones, acting on receptors in the plasma membrane to alter intracellular concentrations of a second messenger, exert many of their primary effects on cellular function over the range of seconds to minutes. occur over long periods of time and can take months or years 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. 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. Other hormonal systems, however, are under direct feedback regulation mechanisms.
25 and Chap. Endocr Rev 1992; 13:453. Another example of this kind is the direct effect of potassium on aldosterone secretion from cells of the adrenal zona glomerulosa (see Chap. 8. Many patients with ectopic corticotropin production have the symptoms and signs of Cushing syndrome, as well as intense pigmentation, caused by hypersecretion of ACTH, and severe depletion of potassium (hypokalemia), caused by the mineralocorticoid action of high serum cortisol concentrations. Endocr Rev 1984; 5:1. 26.
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