Kidneys electrolyte balance

The integrity of mammalian kidneys is vital to body homeostasis, because the kidneys play the principal role in the excretion of metabolic wastes and the regulation of extracellular fluid volume, electrolyte balance, and acid-base... 

The posterior pituitary is innervated by direct nervous stimulation from the hypothalamus, resulting in the release of specific hormones. The hypothalamus synthesizes two hormones, oxytocin and vasopressin. These hormones are stored in and released from the posterior pituitary lobe. Oxytocin exerts two actions (1) it promotes uterine contractions during labor, and (2) it contracts the smooth muscles in the breast to stimulate the release of milk from the mammary gland during lactation. Vasopressin is an antidiuretic hormone (ADH) essential for proper fluid and electrolyte balance in the body. Specifically, vasopressin increases the permeability of the distal convoluted tubules and collecting ducts of the nephrons to water. This causes the kidney to excrete less water in the urine. Consequently, the urine becomes more concentrated as water is conserved. 

Renin-angiotensin-aldosterone system (RAAS) The hormonal system controlled mainly by the kidneys and adrenal glands that regulates blood pressure, blood volume, and electrolyte balance. 

The kidneys are organs specialized to filter the blood. As such, they make an important contribution to the removal of metabolic waste products as well as to maintenance of fluid and electrolyte balance. Specific functions of the kidneys include ... 

Corticosteroids synthesized by the adrenal gland are mineralocorticoids and GC. Min-eralocorticoids regulate fluid and electrolyte balance by affecting ion transport in the kidney. Cortisol, the primary circulating GC in most species (including humans), has many activities, including resistance to stress, regulation of intermediary metabolism, and immunosuppressive and anti-inflammatory effects. GC synthesis and secretion is... 

Aldosterone influences electrolyte balance in the body. Specifically, aldosterone increases the excretion of potassium by the kidney but decreases the excretion of sodium by this organ. One result is the net retention of water. The action of mineralocorticoids tends to increase blood pressure. Basically, the more sodium you retain, the more water you retain. Retaining water tends to increase the fluid level in the vascular system and that increases blood pressure. Think about the pressure changes that happen when you continue to fill a flexible container such as a balloon with water the more water, the greater the pressure in the balloon. You might well imagine that an... 

Mineralocorticoids are endogenous compounds that have an effect on fluid and electrolytic balance in the body, mainly by promoting sodium retention in the kidney. 

While the rate limiting step of the cascade is the renin release, the biological active component is the octapeptide angiotensin n. It is an essential regulator of fluid and electrolyte balance as well as blood pressure. It exerts its actions on various structures like blood vessels, adrenal cortex, kidney and central nervous system. Although at least two different receptor subtypes for angiotensin II have been identified (ATi and AT2) the ATi-subtype is responsible for most of the cardiovascular effects of the agonist. 

Ang II exerts important actions at vascular smooth muscle, adrenal cortex, kidney, heart, and brain. Through these actions, the renin-angiotensin system plays a key role in the regulation of fluid and electrolyte balance and arterial blood pressure. Excessive activity of the renin-angiotensin system can result in hypertension and disorders of fluid and electrolyte homeostasis. 

Certain foreign compounds may cause the retention or excretion of water. Some compounds, such as the drug furosemide, are used therapeutically as diuretics. Other compounds causing diuresis are ethanol, caffeine, and certain mercury compounds such as mersalyl. Diuresis can be the result of a direct effect on the kidney, as with mercury compounds, which inhibit the reabsorption of chloride, whereas other diuretics such as ethanol influence the production of antidiuretic hormone by the pituitary. Changes in electrolyte balance may occur as a result of excessive excretion of an anion or cation. For example, salicylate-induced alkalosis leads to excretion of Na+, and ethylene glycol causes the depletion of calcium, excreted as calcium oxalate. 

Mineralocorticoids are also steroid hormones that are produced by the adrenal cortex. The principal mineralocorticoid in humans is aldosterone. Aldosterone is primarily involved in maintaining fluid and electrolyte balance in the body. This hormone works on the kidneys to increase sodium and water reabsorption and potassium excretion. 

Mineralocorticoid A steroid hormone (e.g., aldosterone) that is important in regulating fluid and electrolyte balance by increasing the reabsorption of sodium from the kidneys. 

The primary function of the renal system is the elimination of waste products, derived either from endogenous metabolism or from the metabolism of xenobiotics. The latter function is discussed in detail in Chapter 10. The kidney also plays an important role in regulation of body homeostasis, regulating extracellular fluid volume, and electrolyte balance. 

Nephrogenic diabetes insipidus, which occurs less often than central diabetes insipidus, is characterized by the inability of the kidneys to reabsorb water into the bloodstream. Treatment with thiazide or potassium-sparing diuretics can help maintain a fluid and electrolyte balance in some individuals with diabetes insipidus. 

While there are no absolute contraindications to lithium, patients with advanced kidney disease or unstable fluid/ electrolyte balance may be more safely treated with an alternative mood stabilizer, such as carbamazepine, valproate, lamotrigine, or olanzapine. 

Nephrotoxicity Kidneys are highly susceptible to toxicants for two reasons A high volume of blood flows through them, and they filtrate large amounts of toxins which can concentrate in the kidney tubules Decreased ability to excrete body wastes Inability to maintain body fluid and electrolyte balance Decreased synthesis of essential hormones (e.g., erythropoietin)... 

In 1989 a renal natriuretic factor (RNF) was detected for the first time and termed urodilatin (P. Schulz-Knappe et at). As examinations have hitherto shown, urodilatin is formed in the medial nephron of the kidney and causes a distad inhibition in the absorption of water and sodium. Its half-life is likewise about 3 minutes. Although ANF is most probably of limited significance for the excretion of sodium and its influence on sodium homoeo-stasis in cases of liver cirrhosis (with or without ascites) has still not been fully clarified, urodilatin is deemed to be important for the regulation of the water and electrolyte balance. (3) (s. tab. 16.5)... 

Another related supportive care issue is electrolyte management. Hyperkalemia, hypermagnesemia, and hyperphosphatemia are common electrolyte disorders in patients with ARF who are unable to use their kidneys to maintain electrolyte balance. This is generally not a serious concern in patients who are achieving electrolyte control via RRT, but electrolytes should be monitored closely in all patients with ARF. 

Maintenance of fluid volume, osmolarity, electrolyte balance, and acid-base status are aU regulated in large part by the kidney. Homeostasis of sodium, potassium, chloride, calcium, magnesium, and phosphorus is altered due to changes in urinary excretion that occur in patients with impaired kidney function. A comprehensive discussion... 

The general processes are manifested by various mechanisms, determined by the type and characteristics of the toxic noxa. Most often met with are a) heavy dehydratation by copious vomiting and diarrheas related to the local damages b) affection of the acid-alkaline and water-electrolytic balance c) acute blood circulation disorders as a consequence of the dehydratation, as well as of the direct injury by some poisons of the vasomotor centers d) syndromes of the central nervous system (consciousness disorders, convulsions, coma, etc.), the liver, the kidneys, the blood, etc., depending on the chemical character of the poison. 

Aldosterone, essentially a corticosteroid in which the methyl group at Cjg is oxidized to a carboxaldehyde, was the last endogenous steroid to be isolated in a form suitable for structural studies. This hormone controls via its action on the kidney both body electrolyte balance and blood volume. A number of modified androstanes, all of which feamre a spirobutyrolactone at C17, act as aldosterone antagonists Those 17-spirobutyrolactones consequently show diuretic and... 

Agents that inhibit steps in the steroidogenic pathway and thus alter the biosynthesis of adrenocortical steroids are discussed, as are synthetic steroids that inhibit glucocorticoid action. The effects of corticosteroids are numerous and widespread, and include alterations in carbohydrate, protein, and lipid metabolism maintenance of fluid and electrolyte balance and preservation of normal function of the cardiovascular system, the immune system, the kidney, skeletal muscle, the endocrine system, and the nervous system. 

In Table 1.1, tests that have been included in regulatory guideline documents (MHW 1990 OECD 1995b, 2002a, 2002b U.S. EPA 1997, 2008) and the IHCPT guidelines are listed. These tests have been selected as measures of metabolic perturbations and tissue injury, and they include measurements of electrolyte balance, carbohydrate metabolism, and some markers of injury to liver, kidney, and other major organs. These tests will be discussed more fully in subsequent chapters. 

The kidneys play important roles in regulating acid-base balance, water and electrolyte balance, blood volume, and blood pressure by interacting with blood hormones. For example, any major change of plasma osmolality is detected by the hypothalamus, which relays messages to the posterior pituitary gland, which then alters the secretion of antidiuretic hormones. Some metabolites (e.g., amino acids and glucose, which are filtered by the glomeruli) are reabsorbed by the tubules and conserved for recirculation. 

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