Water and electrolyte absorption in the gastrointestinal tract

Absorption of water and electrolytes in the gastrointestinal tract are dynamic processes which are closely coupled to each other. The luminal surface of the small intestine is so organized that the surface area available for contact with the intestinal contents is greatly amplified. Water is absorbed passively throughout the GI tract in response to osmotic pressure gradients set up by absorption of solutes, mainly that of sodium chloride, glucose, and amino acids. Sodium may be actively or passively absorbed. In the jejunuma Na+, K+, and Cl- are absorbed mainly by passive solvent drag or convection. In the ileum active absorption of sodium occurs. The soduim absorbed into the cell is actively pumped into the intercellular space by the basolateral membrane Na+ pump. The human colon is responsible for the final modification of the 500-1000 mls of fluid that enter it daily. This fluid is isotonic whith plasma in Na+ concentration. Approximately 80 - 90 percent of the water and more than 90 percent of the Na+ and Cl- that enter the colon daily are absorbed. Several pathological conditions and mechanisms that may result in net fluid and electrolyte secretion have also been discussed (Summary)

Salt wasting in severe tetanus

A 42-year-old man with severe tetanus exhibited two episodes of salt wasting. It was not possible to demonstrate either chronic renal failure or adrenal disease, conditions known to be associated with salt wasting. Studies done in this patient suggested a limitation in maximum tubular reabsorptive rate for sodium. Treatment was purely supportive (AU)

Total body water, extracellular, and plasma volume compartments in sickle cell anaemia

The total body water (TBW), plasma (PV) and extracellular fluid volumes (ECFV) of twenty-nine subjects with sickle cell anaemia, ten of whom were in painful crisis, were studied. During asymtomatic periods (the steady state), the ECFV of subjects with the anaemia is increased when compared with normal controls, because of plasma volume expansion; the interstitial fluid volume (ISFV) is normal, and intra cellular water (ICFV) is diminished by 5 percent of weight. During painful crisis, there was a marked tendency to loss of plasma volume into the interstitial fluid compartment, and the data also suggested that there was acute cellular distruction. Most of the patients in this study managed, however, presumably by compensatory changes in renal function and fluid intake, to maintain a normal plasma volume during painful crisis (AU)

Chemical composition of the whole body and individual tissues of two Jamaican children whose death resulted primarily from malnutrition

A post-mortem chemical analysis has been made of two children who died primarily of malnutrition. The absolute amounts of fat, collagen and non-collagen protein, water, sodium, and potassium found in the whole body and particular organs have been compared with the expected amounts in a normal child of the same height. The results show that the malnourished child is overhydrated with respect to body solids, has lost proportionately more non-collagen protein than collagen protein and may be specifically potassium deficient with respect to nitrogen. (Summary)

Protein requirements in tropical countries: nitrogen losses in sweat and their relation to nitrogen balance

An experiment was undertaken to determine whether high rates of sweating in a tropical climate affect protein requirements by increasing the total nitrogen losses from the body. Six fully acclimatized volunteers were given a diet supplying 50g protein (=8gN) daily. They performed strenuous physical work of a normal nature for an average of 6«h a day for two 5-day periods. During control periods the subjects took minimal exercise and lived in a cool environment. N balance was measured throughout. Rates of sweating were measured by weighing. Whole body sweat was collected and the concentrations were measured of nitrogen, sodium and potassium. During 6«h work approximately 3 liters of sweat were lost, containing on average 0.49gN, 64 m-equiv. Na and 22 m-equiv. K. The N concentration in sweat was 0.20mg/g, which is lower than that found by most other workers. It is suggested that acclimatization is an important factor in reducing N loss by sweating. There was a marked decrease in urinary Na excretion during sweating, which compesated fully for the loss of Na in sweat. Renal compensation for loss of K was less efficient. Because the total N loss in sweat was small, it was not possible to establish with certainty whether it was compensated for by a reduced renal excretion of N. However, after the initial period the subjects were in N balance in spite of the relatively low protein intake. It is concluded that there is no evidence to suggest that heavy sweating under natural conditions in a tropical climate causes a significant increase in protein requirements. (AU)

The excretion of water and solute by malnourished children

Serial measurements were made of the water and solute excretion of 15 malnourished children. Urinary solute excretion and osmolar clearances were low initially and rose during recovery. In most instances there was net tubular reabsorption of water as the children recovered. In one child in whom measurements were made every 2 hours, the diurnal rhythm of solute excretion was poorly marked on admission and restored on recovery. The malnourished children showed an impaired ability to excrete sodium. Evidence is presented to suggest that this is not caused by increased tubular reabsorption. (AU)

The mode of triamterene

Triamterene is a potent diuretic and natriuretic agent which also causes a potassium retention. Its action cannot be through aldosterone antagonism since it acts under conditions when aldosterone activity is negligible. It produces a fall in glomerular filtration rate and rise in serum creatinine. Evidence is presented that it must also have a proximal tubular action (AU)

Magnesium balance studies in marasmic kwashiorkor

Studies of magnesium balance were made on 3 Jamaican infants during recovery from marasmic kwashiorkor. Analysis of muscle biopsy specimens indicated a marked deficit of magnesium as well as potassium in all cases. The serum magnesium level was slightly low in one case. A positive magnesium balance was maintained for several weeks in recovery and was accompanied by low urinary excretion. In one case there was considerable intestinal absorption of magnesium, even in the presence of diarrhea. Efficient absorption of a high oral suppliment tended to overcome renal conservation. Previous analysis has suggested that the deficiency of intracellular electrolytes in wet muscle samples is due partly to the reduced intracellular volume associated with protein loss and partly to a true electrolyte deficit. The positive magnesium balance in recovery is therefore attributable both to intracellular repletion and to tissue growth; the latter tends to be masked clinically by loss of excess body water. Little is known of the additional factor of the repletion of magnesium in bone, but the evidence from animal experiments is that the deficit in bone may be very substantial (AU)

Fluid management in burns

A brief review of the patho-physiology of burns is presented. The main cause of shock following body burns is loss of circulating blood volume either to the exterior or into the burn area. This is best remedied by prompt replacement in accordance with the recommendations of Evans as far as volume and composition are concerned. The hourly urinary output and clinical response of the patient should be the milestones of therapy. Special care must be exercised in the management of the following categories:- children with more than 10 percent body burns, all patients with more than 50 percent involvement, patients over 50 years of age, those with pre-existing cardiovascular, respiratory or renal disease, and those with respiratory burns. Significant nitrogen depletion and anaemia follow most major burns and these must be anticipated or corrected promptly if delayed convalescence and retarded wound healing are to be avoided. (AU)

The management of gastro-enteritis in Jamaican infants

Gastro-enteritis, occurring in a typical country amongst malnourished infants, presents a special problem. Mortality is high and, since those cases which gain admission to hospital must form only a small percentage of the overall incidence prevailing in Jamaica, the control of gastro-enteritis is a serious challenge. Experience gained in the Paediatic Department of the University College Hospital forms the basis of this discussion of the management of infantile gastro-enteritis. The common presenting symptoms and aetiological agents are described and the use of laboratory investigations is discussed in relation to the management of the case. Special emphasis is laid on the management of fluid and electrolyte disturbances, both in a hospital with adequate laboratory facilities and in one which has not these advantages. No detailed discussion of prophylaxis has been attempted, but it is obvious that measures to reduce the incidence of gastro-enteritis are of primary importance in the control of this disease; such measures include the establishment of infant welfare clinics throughout the country where advice on infant feeding and general hygiene can be given. (AU)