Water and Electrolyte Balance

There can be no objection to the ingestion of bulk substances for the purpose of supplementing low-residue modern diets. However, use of irritant purgatives or cathartics is not without hazards. Specifically, there is a risk of laxative dependence, i.e the inability to do without them. Chronic intake of irritant purgatives disrupts the water and electrolyte balance of the body and can thus cause symptoms of illness (e.g., cardiac arrhythmias secondary to hypokalemia). 

Farkkila AM, Iivanainen MV, Farkkila MA. Disturbance of the water and electrolyte balance during high-dose interferon treatment. J Interferon Res 1990 10(2) 221-7. 

Alhenc-Gelas, F., and Corvol, P. (2000). In Handbook of Physiology Endocrine Regulation Of Water And Electrolyte Balance (J. C. S. Fray, ed.), pp. 81-103. Oxford University Press, New York. 

Reisin, I. L. Rotunno, C. A. (1981). Water and electrolyte balance in protoscoleces of Echinococcus granulosus incubated in vitro general procedures for the determination of water, sodium, potassium and chloride in protoscoleces. International Journal for Parasitology, 11 399-404. 

What is clear, however, is that the consequences of hormone imbalance result in profound aberrations in homeostasis. For instance, changes in water, acid-base, and electrolyte balance in the human organism have far-reaching medical implications. The clinical biochemistry laboratory performs numerous acid-base, electrolyte, and osmolarity determinations every day, and the management of the patient depends in a major way on such clinical-chemical data. For this reason, this chapter contains a discourse on water and electrolyte balance, presented from a clinical and biochemical point of view. 

The surface of the mucosa is relatively smooth as there are no intestinal villi. Crypts of Lieberktlhn are present. Goblet cells account for more of the epithehal cells than in the small intestine. The mammalian large intestine is important for the maintenance of water and electrolyte balance. Its primary function is the reabsorption of water, sodium, chloride and volatile fatty acids it secretes potassium and bicarbonate. 

Lelthead, C.S. (1964) Disorders of water and electrolyte balance. In Heat Stress and Heat Disorders (Leithead, C.S. Lind, A.R., authors), pp. 141-177, F.A. Davis Company, Philadelphia, PA. 

Four general pathophysiologic mechanisms disrupt water and electrolyte balance, leading to diarrhea. These four mechanisms are the basis of diagnosis and therapy. They are (1) a change in active ion transport by either decreased sodium absorption or increased chloride secretion (2) a change in intestinal motility (3) an increase in luminal osmolarity and (4) an increase in tissue hydrostatic pressure. These mechanisms have been related to four broad clinical diarrheal groups secretory, osmotic, exudative, and altered intestinal transit. 

Defects in the cerebral functions and disturbances in the water and electrolyte balance are considered to be the earliest and most reliable signs of commencing decompensation in a severe liver disease, particularly cirrhosis. 

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)... 

Ultimately, decompensation of the water and electrolyte balance is the result of (1.) splanchnic and peripheral arterial vasodilation, (2.) subsequent marked reduction in the effective arterial blood volume, (3.) increase in renin, aldosterone, vasopressin and noradrenaline, 4.) renal vasoconstriction with retention of sodium and water, and (5.) inadequate compensation of the plasma volume as a result of progressive hypalbuminaemia. 

Disorders of cerebral functions on the one hand and of the water and electrolyte balance on the other hand are the earliest and most reliable hints of the onset of decompensation in severe liver disease, especially cirrhosis. In clinical terms, they can be easily diagnosed as latent hepatic encephalopathy (by carrying out psychometric tests) and/or latent oedema (by recording the increase in body weight). For this reason, these examination methods are also of fundamental importance in the follow-up of chronic liver disease, (s. fig. 15.3)... 

Diet The diet should be evenly balanced and in accordance with the principles of present-day dietetics it must also be tolerated by the patient. There is no special diet for viral hepatitis patients. The water and electrolyte balance is often disrupted in cases of acute viral hepatitis, possibly with the occurrence of oedemas and ascites (so-called hepatitis oedematosa) (48, 77, 131) (s. p. 297) or impaired renal function (60, 120) - as is recognizable from the diuresis which normally develops at the onset of the convalescence phase. An even balance of water and electrolytes should be maintained - this is very much supported by the patient lying flat. In the event of inadequate nutrition or malnutrition, particularly when nausea and vomiting occur, substitution measures are advisable (e.g. vitamins, glucose and electrolyte infusions). 

Impairment of cerebral functions and disturbances of the water and electrolyte balance are the two most important and most common manifestations of decompensated liver cirrhosis. They may be reliably detected at an early stage by means of daily body weight control and simple psychometric tests. A documentation sheet filled in by the patient has proved to be worthwhile latent oedemas or the onset of ascites as well as latent encephalopathy can be detected in this way and thus treated at an early stage. Longterm standing leads to a reduction of natriuresis with subsequent water retention and a deterioration of renal blood flow (like a vicious circle). This is caused by activation of the RAAS and the sympathetic nervous system. Such a dangerous situation (which can arise for example after two hours of standing at a sports event with excessive emotional participation) is often underrated, as we ourselves observed in several patients (s. p. 292) (s. fig. 15.3) (see chapter 16 )... 

In the fasting state, 9 L of fluid enters the proximal small intestine each day. Of this fluid, 2 L are ingested through diet, while the remainder consists of internal secretions. Because of meal content, duodenal chyme is usually hypertonic. When chyme reaches the ileum, the osmolality adjusts to that of plasma, with most dietary fat, carbohydrate, and protein being absorbed. The volume of ileal chyme decreases to about 1 L/day upon entering the colon, which is further reduced by colonic absorption to 100 mL daily. If the small intestine water absorption capacity is exceeded, chyme overloads the colon, resulting in diarrhea. In humans, the colon absorptive capacity is about 5 L daily. Colonic fluid transport is critical to water and electrolyte balance. 

The possible relationship between tryptophan and sodium ions has been considered in a number of studies. Herken and Weber165 reported that under certain conditions tryptophan injections intraperitoneally to rats led to a reduction of elimination of Na++. Subsequently, Reuter et al.166 analyzed the alterations of water and electrolyte balances by the use of clearance experiments. The fractional Na++ reabsorption increases, with no increase in the absolute tubular sodium transport rate since the significant reduced plasma-sodium concentration led to a decreased sodium load. The most probable cause of the decreased plasma-sodium concentrations seemed to be retention of sodium-free water under the conditions of infusion. The water retention is compatible with the antidiuretic effect of serotonin. Another relationship between tryptophan and sodium has been reported on the effects of each agent alone or together in vivo or in vitro, on in vitro hepatic nuclear tryptophan receptor binding and hepatic protein synthesis.167 168 This has been considered in detail in Chapter 4. 

A significant study using extracts of rat cardiac atrial tissue produced copious excretion of urine, Na+ and Cl- at levels 30 times above normal on being injected into rats. The discovery of a saluretic peptide hormone thus established the heart as an endocrine gland with strong effects on water and electrolyte balance (Na+ and Cl-). Now named Atrial Natriuretic Factor (ANF), it may be useful in treating CHF patients in whom levels have been shown to be increased, yet are associated with decreased cardiac output. The normal effect of ANF infusion is to increase water, Na+, and K+ excretion and inhibit it for aldosterone and cortisone. Most of these effects do not occur in CHF patients, which may be the reason for the edema accompanying CHF. Why that is, however, remains to be seen. When the reasons become known, it may be possible to find a way around the CHF patient s inability to respond to ANF. That should solve many problems. 

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. 

Cortisone Controls metabolism of proteins, carbohydrates, lipids controls water and electrolyte balances controls inflammation... 

CLINICAL SIGNIFICANCE OF ELECTROLYTES 5.1. Water and Electrolyte Balance... 

The maintainance of water and electrolyte balance is one of the most important therapeutic activities in the clinic. Normal diet and adequate fluid intake cover one s requirements. Imbalance (see above) has to be verified by electrolyte determination in blood serum as well as in urine and possibly by other diagnostic parameters. Water equilibrium must be attained and compensation of electrolyte deficiency should be performed by oral or parenteral application of medicaments containing the required amount of electrolytes. A very large number of solutions and tablets is available to solve these clinical problems. For further details, see Refs. 27 and 41-44. 

Body Fluid Compartments Regulation of Water and Electrolyte Balance Movement of Water and Electrolytes Factors Regulating Movement Imbalances of Water and Electrolytes Water Depletion Water Excess Sodium Depletion Sodium Excess Potassium Depletion Potassium Excess Chloride... 

REGULATION OF WATER AND ELECTROLYTE BALANCE. Basically, water (1) enters the body via the digestive tract as liquid or food, (2) moves into the blood and tissue, and (3) leaves via the kidneys, skin, lungs, or feces. Water entering and leaving the body is under rigid... 

It is evident that a marvelous organ, the kidney, is largely responsible for regulating the water and electrolyte balance of the body. Each kidney contains about one million minute functional units called nephrons. As the blood passes through these nephrons, they select, reject, conserve, and eliminate water, electrolytes, and other substances in order to maintain the volume and the composition of the extracellular fluid. Each day they rejuvenate ab)OUt 50 gal (190 liter) of blood. Moreover, they function to regulate red blood cell production, aldosterone secretion, blood pressure, and calcium metabwlism. So important is their function that without it death results in 8 to 14 days. 

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