Sodium content, human body

The average Na+ content of the human body is 60 mEq/kg, of which 50% is in extracellular fluid, 40% is in bone, and 10% is intracellular. The chief dietary source of sodium is salt added in cooking. Excess sodium is largely excreted in the urine, although some is lost in perspiration. Gastrointestinal losses are small except in diarrhea. 

Sea lettuces which draw from the sea contain wealth of mineral elements (Table 5.4). Calcium, one of the most important minerals essential for human body, is accumulated in sea lettuces at a higher level compared with milk, brown rice, spinach, peanuts, and lentils (MacArtain et ah, 2007). Calcium contents in Ulva lactuca, Ulva reticulata, Ulva fasciata were 32.5, 147, and 0.47 mg/100 g edible portion, respectively. Moreover, potassium and sodium are known as electrolytes because their ability to dissociate into positively and negatively charged ions when dissolved in water. Potassium is the major cation of intracellular fluid. Together with sodium, it maintains normal water balance. In addition, potassium also promotes cellular growth and maintains normal blood pressure. Potential source of potassium is Ulva reticulata, which contains 1540 mg potassium per 100 g edible portion (Ratana-arpom and Chirapart, 2006). 

The total sodium and potassium contents in the human body are about 70-100 g and 140-180 g, respectively. Sodium is found predominantly in the extracellular space, while potassium is located mainly inside the cells. Large amounts of sodium and potassium ions are found in the gastric juices. 

Salt and water balance are closely related. Water can remain in the ECF only if accompanied by sodium ions, which are the major cations in the ECF and form 90% of the total cation content. If water is added to the plasma without an appropriate amount of sodium ions to maintain normal osmotic pressure, the water will leave the ECF and move into the body cells. Although thirst is known to be a powerful stimulus to drink and replace the lost water, the corresponding stimulus for salt intake or salt appetite is poorly understood and is probably of minor importance in human subjects. 

Essentiality and Toxicity for Man For humans, sodium (and chlorine) are essential nutrients, the deficiency of which frequently and acutely leads to premature death, usually from circulatory failure. The second most frequent consequence is diarrhea. The physiology of man is, consequently, characterized by multiple control mechanisms which act to maintain and control the NaCl content and concentrations within the body. Sodium deficiency symptoms in humans are not well known nonetheless, a sodium chloride deficit as a common cause of death is quite treatable with minimum effort, provided that some basic principles are remembered. Body weight change is the best indicator of a sodium deficit. Except in the presence of imminent circulatory collapse, oral treatment is usually possible. Except in case of cholera, the colon usually responds to aldosterone, and quite low sodium concentrations are adequate for the rehydration solutions. In the case of cholera, near-isotonic solutions are necessary (Harper et al. 1997). 

The chloride content of human tissue is 1.1 g/kg body weight and the plasma concentration is 98-106 mmol/1. Chloride serves as a counter ion for sodium in extracellular fiuid and for hydrogen ions in gastric juice. Chloride absorption is as rapid as its excretion in the urine. The minimum intake of chloride largely corresponds on a molar basis to the sodium requirement. 

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