Best Practice & Research Clinical Endocrinology & Metabolism
1Disorders of body water homeostasis
Section snippets
Body fluid compartments
Water constitutes approximately 55–65% of body weight, varying somewhat with age, sex and amount of body fat, and therefore constitutes the largest single constituent of the body. Total body water (TBW) is distributed between the intracellular fluid (ICF) and the ECF compartments. Estimates of the relative sizes of these two important pools differ significantly depending on the tracer used to measure the ECF volume, but most studies in animals and man have suggested that 55–65% (or just under
Total and effective osmolality
Osmolality is defined as the concentration of all of the solutes in a given weight of water. Plasma osmolality can be measured directly (via determination of freezing point depression or vapour pressure because each of these are colligative properties of the number of free solute particles in a given volume of plasma), or estimated as:Both methods produce comparable results under most conditions, as will simply
Water metabolism
Water metabolism represents a balance between the intake and excretion of water. Each side of this balance equation can be considered to consist of a ‘regulated’ and an ‘unregulated’ component, the magnitudes of which can vary quite markedly under different physiological and pathophysiological conditions. The unregulated component of water intake consists of the intrinsic water content of ingested foods, the consumption of beverages primarily for reasons of palatability or desired secondary
Sodium metabolism
Maintenance of sodium homeostasis requires a simple balance between intake and excretion of Na+. As in the case of water metabolism, it is possible to define regulated and unregulated components of both Na+ intake and Na+ excretion. Unlike water intake, however, there is little evidence in humans to support a significant role for regulated Na+ intake, with the possible exception of some pathological conditions. Consequently, there is an even greater dependence on mechanisms for regulated renal
Pathogenesis
Hyperosmolality indicates a deficiency of water relative to solute in the ECF. Because water moves freely between the ICF and ECF, this also indicates a deficiency of TBW relative to total body solute. Although an excess of body sodium can cause hypernatraemia, the vast majority of cases are due to losses of body water in excess of body solutes, caused by either insufficient water intake or excessive water excretion. Consequently, most of the disorders causing hyperosmolality are those
Pathogenesis
Hypo-osmolality indicates excess water relative to solute in the ECF; because water moves freely between ECF and ICF, this also indicates an excess of TBW relative to total body solute. Imbalances between body water and solute can be generated either by depletion of body solute more than body water, or by dilution of body solute from increases in body water more than body solute (Table 4).3 This represents an oversimplification, because most hypo-osmolar states include components of both solute
References (65)
New approach to disturbances in the plasma sodium concentration
American Journal of Medicine
(1986)A microregulatory analysis of spontaneous fluid intake in humans: evidence that the amount of liquid ingested and its timing is mainly governed by feeding
Physiology and Behavior
(1988)Disorders of antidiuretic hormone secretion
Clinical Endocrinology and Metabolism
(1985)- et al.
Influence of the emetic reflex on vasopressin release in man
Kidney International
(1979) - et al.
Neurogenic disorders of osmoregulation
American Journal of Medicine
(1982) - et al.
Hyponatremia: evaluating the correction factor for hyperglycemia
American Journal of Medicine
(1999) Diabetes insipidus
Endocrinology and Metabolism Clinics of North America
(1995)- et al.
Clinical assessment of extracellular fluid volume in hyponatremia
American Journal of Medicine
(1987) - et al.
The syndrome of inappropriate secretion of antidiuretic hormone
American Journal of Medicine
(1967) - et al.
Hyponatremia causes large sustained reductions in brain content of multiple organic osmolytes in rats
Brain Research
(1991)
Epidemiology, pathophysiology, and management of hyponatremic encephalopathy
American Journal of Medicine
Compartmentation of body water
The syndrome of inappropriate antidiuretic hormone secretion and other hypoosmolar disorders
Effect of insulin on osmoregulation of vasopressin
American Journal of Physiology
Body water and osmolality
Physiology and pathophysiology of thirst and sodium appetite
Water intake and body fluids
Thirst and vasopressin function in normal and disordered states of water balance
Journal of Laboratory and Clinical Medicine
The osmotic thresholds for thirst and vasopressin release are similar in healthy man
Clinical Science (London)
Angiotensin II-induced thirst and vasopressin release in man
Clinical Science (London)
Posterior pituitary
Molecular physiology of urinary concentrating mechanism: regulation of aquaporin water channels by vasopressin
American Journal of Physiology
The regulation of vasopressin function in health and disease
Recent Progress in Hormone Research
Body sodium and extracellular fluid volume
The Hunger for Salt: An Anthropological, Physiological and Medical Analysis
A great craving for salt by a child with cortico-adrenal insufficiency
JAMA
The adrenal cortex
Sodium metabolism
Tubular sodium transport
Glomerular filtration
Aldosterone-mediated regulation of ENaC alpha, beta, and gamma subunit proteins in rat kidney
Journal of Clinical Investigation
Effect of osmolality on aldosterone secretion
Endocrinology
Cited by (348)
Etiology and Management of Edema: A Review
2023, Advances in Kidney Disease and HealthParticipation of the angiotensinergic and vasopressinergic mechanisms in the maintenance of cardiorespiratory parameters in sodium depleted rats
2022, HeliyonCitation Excerpt :Disruption of body fluids regulation is a very common issue encountered in the medical practice. This is mainly due to several illness and conditions that may potentially affect the control of intake and output of water and electrolytes, such as hyponatremia, disrupting this finely balanced mechanism [1]. Hyponatremia occurs when the concentration of sodium in the blood is low, causing a hydroelectrolyte imbalance in the body.
Syndrome of inappropriate antidiuretic hormone secretion
2022, Medicina Clinica