Hyponatremia – serum sodium concentration less than normal

Hyponatremia is a common electrolyte disorder defined as a serum sodium level of less than 135 mEq per L is the most common disorder of body fluid and electrolyte balance encounte-red in clinical practice.

It is associated with increased mortality, morbidity and length of hospital stay in patients presenting with a range of conditions. Hyponatremia is therefore both common and important.

Hyponatremia results from the inability of the kidney to excrete a water load or excess water intake. Water intake depends upon thirst mechanism. Thirst is stimulated by increase in osmolality.

Thirst is sensed by osmoreceptors located in the hypothalamus and leads to the release of anti-diuretic hormone (vasopressin) from the posterior pituitary. Anti-diuretic hormone acts on the V2 receptors located at the basolateral aspect of the collecting duct cells and leads to increased aquaporin expression on the luminal aspect of the collecting duct cells which increases water absorption and abolishes thirst.

The most common causes of hyponatremia are the syndrome of inappropriate anti-diuresis (SIAD), diuretic use, polydipsia, adrenal insufficiency, hypovolemia, heart failure, and liver cirrhosis (the latter two are often collectively referred to as “hypervolemic hyponatremia”).

The most common classification system for hyponatremia is based on volume status:
*hypovolemic (decreased total body water with greater decrease in sodium level)
*euvolemic (increased total body water with normal sodium level)
*hypervolemic (increased total body water compared with sodium)
Hyponatremia – serum sodium concentration less than normal

Sodium in extracellular fluid

Sodium chloride is primarily restricted to the extracellular space. When sodium is ingested without water the excess sodium will remain in the extracellular space, where it will raise the plasma sodium concentration and the plasma osmolality.

The increase in osmolality will result in the osmotic movement of water out of the cells into the extracellular space until the osmolality is the same in two compartments.

As a result, the glomerular filtration rate increases, and the excess sodium and water are excreted by the kidney to restore the normal extracellular volume.

A low sodium diet leads to a transient negative sodium balance, thereby reducing extracellular volume, a process that activates the sodium-conserving mechanisms of the kidney.

Because sodium is the major extracellular cation, shifts in serum sodium levels are usually inversely correlated with the hydration state of the extracellular fluid compartment.

The pathophysiology of hyponatremia then is usually expansion of body fluids leading to excess total body water. Symptomatic hyponatremia usually does not occur until the serum is below 120 to 125 mEq/L.

In the normal individual, the kidney behaves as though extracellular volume was the regulatory stimulus articulating renal excretion with salt intake.
Extra note:
Osmotic pressure is measured in milliosmoles. When the number of particles is measured per kilogram of solvent, the correct term s osmolality, when measured per liter of solvent, the correct term is osmolarity. Sodium in extracellular fluid

Electrolytes in the Human Body

Electrolytes are solutes that contain a charge in aqueous solutions. Most acids, bases and salts are soluble in water are electrolytes.

Electrolytes are negatively or positively charged ion. Although many substances in the body are electrolytes, in nutrition and in sports drinks, the term electrolytes refers to the three principal electrolytes in body fluids: sodium, potassium and chloride.

These are electrolytes are among the most commonly monitored electrolytes in clinical practice.

These electrolytes are important in maintaining fluid balance and allowing nerve impulses to travel throughout out bodies, signaling the activities that are essential for life.

Sodium and potassium carry a positive charge, and chloride carries a negative charge.

The concentration of sodium, potassium and chloride inside a cell differ dramatically from those outside the cell.

An electrolyte is stored either intracellular or extracellular.

Potassium is the principal positively charged intracellular ion, sodium is the most abundant positively charged extracellular and chloride is the principal negatively charged extracellular ion.

Fluid move though the body continuously. The heart pumps the blood, pressure is extend on the vessels from outside the body, and muscles relax and contract to help move the fluid through the vascular system. Fluid moves into and out of the cells and the extracellular spaces by osmotic pressure.

Osmotic pressure is determined by the concentration of the electrolytes and other solutes in water.

The greater the difference in charge between two regions, the greater is potential for ions to move to their oppositely charged regions.
Electrolytes in the Human Body

Sodium: Recommendation and Food Sources

Sodium: Recommendation and Food Sources
We rarely eat too little sodium; in fact, most of us eat substantially more than we need. Actual sodium requirements by the body are relatively small – only a few hundred milligrams daily.

In order to make sure that the diet contains adequate amounts of all nutrient, however, the Food and Nutrition Board set the Al for sodium for adults at 1,500 milligrams per day.

The Tolerable Upper Intake Level for sodium is 2,300 milligrams per day. This suggested maximum level is echoed in the American Heart Association’s Diet and Lifestyle Recommendations.

Food sources
The typical American diet contains 3,000 to 6,000 milligrams of sodium daily. Not only do Americans consumes more than the recommended amounts of sodium, but they also are poor judges of the amount of sodium in their diets.

Surprisingly, processed foods – not table salt - contribute the most sodium.

70 % of the sodium in the American diet comes from processed foods. In addition to being higher in sodium, these foods are often lacking in many other nutrients such as fiber and antioxidants.

Soy sauce and other sauces; pickled foods; salty or smoked meats, cheese and fish; salted snack foods; bullion cubes and canned and instant soups are all high sodium foods.

Seasoning based in salt ( e.g. lemon salt and seasoning salt) and those containing the flavor enhancer monosodium glutamate (MSG) are also high in sodium.

If your diet is cased on Asian foods that contain liberal amounts of soy sauce and MSG you could be taking in 12,000 to 16,000 milligrams of sodium per day.

Your intestinal tract absorbs nearly all dietary sodium, which then travels throughout the body in the bloodstream. Your kidneys, those remarkable organ, retain the exact amount of sodium the body needs and excrete the excess sodium in the urine along with water.

Taking in too much sodium and not enough water can worsen dehydration. The old practice of giving athletes salt tablets before or after exercise is unnecessary and possibly harmful.

On the other hand, radical sodium restriction is not a good idea either. Even though most American consume to much sodium, severe sodium restriction can limit the availability of other essential nutrients such as vitamin B6, calcium, iron and magnesium.
Sodium: Recommendation and Food Sources

Sodium in Human Body

Sodium in Human Body
Sodium is capable of permeating the cell membrane and muscle contraction and nerve transmission involve a temporary exchange of extracellular sodium and intracellular potassium.

The subsequent transfer of sodium out of the cell is by means of an active mechanism or pump.

A very small amount of sodium occurs intracellularly.

In bone sodium is bound for the most part on the surface of bone crystals. The amount present in bone is by no means small and accounts for 30 to 45 percent of total body sodium.

This reservoir apparently is part of the active labile sodium pool in the body.

Sodium metabolism is regulated primarily by aldosterone, a hormone of the adrenal cortex that promotes the reabsorption of sodium from the kidney tubules.

If the absence of this hormone, sodium excretion is increased and symptoms of deficiency ensue.

Other adrenalin minerolocorticoids, deoxycorticosterone and hydrocortisone, are involved in regulation of sodium excretion but are less potent in action.
Sodium in Human Body

Sodium

Sodium
The value of salt has been recognized for centuries. The common expressions of “salt of the earth” and even the word “salary” all derive from high value placed upon salt throughout history.

The requirement for sodium is not well defined, but human dietaries generally contain more sodium than necessary.

Tissue formation, as in growth, requires about 1.1 -1.2 mg/kg of tissue gained; the requirement for maintenance should be considerably less.

Intakes vary widely; about 10 gm NaCl/day appears to be usual for most Americans, whereas intakes of 30 – 40 gm/day are not uncommon in Oriental countries where soy sauces and sodium glutamate are flavored as flavoring agents.

The human body contains about 1.8 gm Na/kg at free bodyweight, most of which is present in extracellular fluids.

The content of serum normally is about 140 mEg/liter .

Since sodium is the chief cation of the extracellular fluid, the control of the body fluid osmolarity and therefore body fluid volume is largely dependent on sodium ions and the ratio of sodium to other ions.
Sodium

Main Elements: Sodium

Main Elements: Sodium
The sodium content of the body is 1.4 kg. Sodium is present mostly as an extracellular constituent and maintains the osmotic pressure and maintains the osmotic pressure of the extracellular fluid.

In addition, it activates some enzymes, such as amylase.

Sodium absorption is rapids; it starts 3 – 6 min after intake and is completed within 3 h.

Daily intake of sodium averages 2.5 g (females) to 3.3 g (males); the adult’s minimum requirement ranges form 1.3 – 1.6 g/day (equal to 3.3 – 4.0 g/day NaCl).

The intake of too little or too much sodium can result in serious disorders.

From a nutritional standpoint, the daily sodium intake should be limited o 2.3 g (equivalent to 6 g NaCl).

A low intake of sodium can be achieved by a nonsalty diet or by using diet salt.
Main Elements: Sodium

Salt in the Diet

Salt in the Diet
The substance we call salt is the chemical compound sodium chloride. Salt also contains small amounts of other trace elements including calcium, magnesium and iodine.

Salt in the diet comes mainly from processed foods such as crisps, nuts, cheese, pickled vegetables, sauces and smoked foods. It is also added to food during preparation, cooking and at the table. Small quantity occurs naturally in some foods. Nobody is quite sure exactly how much salt we need to eat, but it is relatively small amount.

Salt in children’s diet
Babies need very little salt. Their kidneys are not well enough develop to get rid of extra salt. The main problem is hypernatraemia, which causes dehydration with symptoms of irritability, poor appetite and sometimes convulsions. If hypernatraemia is not treated it can cause permanent brain damage and can be fatal. Children who have high salt intakes also develop a taste for salty foods which is hard to shake off in later life.

Salt and health
There is some weak evidence that eating too much salt is connected with high blood pressure. In countries where peop0le eat a lot of salt there is high blood pressure, and where they do not eat a lot of salt high blood pressure is not a problem. This has not, however, been shown within countries. For examples, in the United Kingdom it has never been shown that people who eat a lot of salt are more likely to have high blood pressure than those who do not. The mechanism by which salt might cause high blood pressure is not understood either, although some evidence suggests that it is the sodium component which people react to. If this so, care may need to be taken over the consumption of other sodium salts on food. These include sodium nitrate, sodium caseinate, monosodium glutamate and a number of others.
Salt in the Diet