Metabolic homeostasis abnormalities

Electrolytes are involved in many metabolic and homeostatic functions, including enzymatic and biochemical reactions, maintenance of cell membrane structure and function, neurotransmission, hormone function, muscle contraction, cardiovascular function, bone composition, and fluid homeostasis. The causes of electrolyte abnormalities in patients receiving PN may be multifactorial, including altered absorption and distribution excessive or inadequate intake altered hormonal, neurologic, and homeostatic mechanisms altered excretion via gastrointestinal and renal losses changes in fluid status and fluid shifts and medications. 

Two inherited human diseases that represent abnormal copper metabolism are Menkes syndrome and Wilson s disease. Menkes syndrome, with symptoms similar to those of copper deficiency, is characterized by a progressive brain disease, abnormally low copper concentrations in liver and other tissues, and diminished ability to transfer copper across the absorptive cells of the intestinal mucosa (USEPA 1980 Aaseth and Norseth 1986). Wilson s disease (hepatolenticular degeneration) is the only significant example of copper toxicity in humans. Wilson s disease is an autosomal recessive disorder that affects normal copper homeostasis and is characterized by excessive... 

Maintenance of water homeostasis is paramount to life for all organisms. In mammals, the maintenance of osmotic pressure and water distribution in the various body fluid compartments is primarily a function of the four major electrolytes, Na", K , Cl", and HCOi". In addition to water homeostasis, these electrolytes play an important role in the maintenance of pH, proper heart and muscle function, oxidation-reduction reactions, and as cofactors for enzymes. Indeed, there are almost no metabolic processes that are not dependent on or affected by electrolytes. Abnormal concentrations of electrolytes may be either the cause or the consequence of a variety of disorders. Thus determination of electrolytes is one of the most important functions of the clinical laboratory. Interpretation of abnormal osmolality and acid-base values requires specific knowledge of the electrolytes. Because of their physiological and clinical interrelationship, this chapter discusses determination. of electrolytes, osmolality, acid-base status, and blood oxygenation. 

Calcium and phosphorus balance is mediated through the complex interplay of hormones and their effects on bone, the Gi tract, kidney, and parathyroid gland. What begins as relatively minor imbalances in phosphorus and calcium homeostasis leads to secondary hyperparathyroidism (sHPT) in the short term and ultimately renal osteodystrophy (ROD) if these metabolic abnormalities are not corrected. 

Although AD is not usually considered a metabolic disorder, evidence supporting this hypothesis exists. Abnormalities in a number of brain enzymes involved in glucose metabolism (Friedland et al. 1989 Kalaria and Harik, 1989) and in Ca + homeostasis in AD have been detected (Martin et al., 1989). Thus, ALC may be useful to attenuate cellular energy deficiency in aging and AD. 

---