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Renal Disease; Fluid and Electrolyte Disorders
Published in John S. Axford, Chris A. O'Callaghan, Medicine for Finals and Beyond, 2023
As sodium is the major extracellular ion, it is the major determinant of body water content. Generally, the body will maintain osmolality, even at the expense of volume changes. This makes sense because a small change in body water content is tolerated by changes in vessel tone, but a change in the osmotic gradient across cell membranes has severe effects on cells, such as causing seizures in the brain. Control of osmolality: Osmoreceptors in the hypothalamus detect changes in osmolality and trigger changes in water intake by thirst and in water excretion by altering vasopressin (ADH) secretion. This maintains osmolality by changing water handling but does not control body osmolyte content.Control of volume: Volume receptors in the circulation detect stretch. Sodium handling by the kidney is influenced especially by angiotensin II and aldosterone. Because osmolality will normally be maintained, the total body water volume is controlled by changing the amount of sodium in the body. For example, if body volume is low, the kidney retains sodium, which increases plasma osmolality. The osmolality regulating system then causes more water to be drunk and less to be excreted by the kidney and the result is an increase in total body water.
Hyponatremia in pregnancy
Published in Nadia Barghouthi, Jessica Perini, Endocrine Diseases in Pregnancy and the Postpartum Period, 2021
Anthony Parravani, Bethany Pellegrino
Nonpregnant state, maintenance of serum osmolality and sodium:Under nonpregnant conditions, serum osmolality is maintained within a narrow range of 275–295 mOsm/L.Any changes in serum osmolality are sensed by osmoreceptors which respond to correct the change.An increase in serum osmolality by 1–2% results in the release of ADH from the posterior pituitary, which acts on the Arginine Vasopressin Receptor 2 (AVPR2) on the basolateral membrane of the collecting ducts in the kidneys. This leads to the upregulation of aquaporin 2 channels and increased water absorption by the kidneys.Any increase in serum osmolality also stimulates the thirst center in the hypothalamus, resulting in water intake to assist in correction of the hypertonic state.4
Tubular Function
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The release of ADH from the posterior pituitary is under the control of baroreceptor and osmoreceptor reflexes that act via the hypothalamus. Hypothalamic osmoreceptors sense changes in plasma osmotic pressure. A rise in osmotic pressure increases ADH secretion, and a fall in osmotic pressure reduces ADH secretion. The set point of the system is defined as the plasma osmolality at which ADH secretion begins to increase and the slope of this relationship is quite steep, reflecting the sensitivity of the system, and below this, virtually no ADH is released. The set point varies from 280 to 295 mOsm/kg H2O. A fall in plasma volume is detected by arterial, venous and, particularly, cardiac atrial baroreceptors, which reduce their afferent firing rate to the hypothalamus, in turn increasing ADH release from the posterior pituitary. The sensitivity of the baroreceptor mechanism is less than that of osmoreceptors. A 5%–10% decrease in blood volume is required before ADH secretion is stimulated. Changes in blood volume also influence the secretion of ADH in response to changes in plasma osmolality. When a decrease in blood volume occurs, the set point shifts to lower plasma osmolality values and the slope is steeper. This allows the kidney to conserve water, even though the water retention will reduce the osmolality of body fluids. The opposite response occurs with an increase in blood volume and the set point shifts to higher osmolality values and the slope is decreased. The same osmoreceptors and baroreceptors control the sensation of thirst via hypothalamic centres close to those producing ADH.
Mechanisms involved in the cardiovascular effects caused by acute osmotic stimulation in conscious rats
Published in Stress, 2020
Eduardo Albino Trindade Fortaleza, Cristiane Busnardo, Aline Fassini, Ivaldo Jesus Almeida Belém-Filho, Gislaine Almeida-Pereira, José Antunes-Rodrigues, Fernando Morgan Aguiar Corrêa
Osmoreceptors are found in forebrain areas, such as the subfornical organ and organum vasculosum of the lamina terminalis (Bourque, 2008; Broadwell & Brightman, 1976; McKinley et al., 1983). Additionally, there are peripheral osmoreceptors in the liver, mouth, splanchnic circulation, and hepatoportal region (Bisset & Chowdrey, 1988; Bourque et al., 1994; Hosomi & Morita, 1996). When stimulated, they activate the hypothalamic supraoptic nucleus (SON) and the paraventricular nucleus (PVN) to regulate vasopressin (AVP) and oxytocin (OT) secretion, and the central sympathetic neurocircuitry (Hussy, Deleuze, Desarmenien, & Moos, 2000; Larsen & Mikkelsen, 1995; Onaka & Yagi, 2001; Weiss & Hatton, 1990), integrating cardiovascular control and body fluid balance (Haberich, 1968; Herbert, Moga, & Saper, 1990; Kobashi & Adachi, 1985; Ricardo & Koh, 1978; Saper, Reis, & Joh, 1983; Sawchenko & Swanson, 1982; Stocker, Osborn, & Carmichael, 2008; Toney, Chen, Cato, & Stocker, 2003; Torvik, 1956; van der Kooy & Koda, 1983).
Activation of tumor cell integrin αvβ3 by radiation and reversal of activation by chemically modified tetraiodothyroacetic acid (tetrac)
Published in Endocrine Research, 2018
John T. Leith, Aleck Hercbergs, Susan Kenney, Shaker A. Mousa, Paul J. Davis
The surprising finding in the current studies is that integrin αvβ3 undergoes a substantial physical change (“activation”) acutely in response to radiation exposure. This change has not previously been described as a feature of cell response to radiation exposure. While such a change is likely to generate intracellular signals via stress-activated protein kinases and other factors cited above, the change may also radically change the complex cell–cell and cell–ECM protein interactions of the integrin. Such changes could involve αvβ3-dependent alterations in cell permeability,24 resulting in cellular osmolar stress that inhibits DNA replication25 and contributes to radioresistance. Integrins are known to be osmoreceptors.26 We also speculate that important radiation-induced changes in abundance and function of cell surface αvβ3 might alter the physical state of tumor cell microenvironment sufficiently to reduce oxygen diffusion and metabolic substrate availability to cells. This would also serve to inhibit cell division and radiosensitivity.
Psychogenic polydipsia associated with sertraline treatment: a case report
Published in Psychiatry and Clinical Psychopharmacology, 2019
Esra Okyar, Leyla Bozatlı, Işık Görker, Serap Okyar
The regulation of the hypothalamic thirst center is thought to be impaired in the pathogenesis [8]. If the solute concentration in the extracellular fluid increases, the osmoreceptors in the hypothalamus generate an output signal to increase the release of ADH from the posterior pituitary. If the solute concentration in the extracellular fluid decreases, there is a decrease in the release of ADH [14]. It is thought that patients with PP have inappropriate ADH release or inadequate response of kidneys to ADH. While ADH levels are high in PP, the osmotic threshold for ADH release is reduced [8]. Hippocampal dysregulation of fluid consumption behavior is another cause of PP [15].