Sodium Natrium Na At.No. 11 Atomic mass 22.98

SODIUM Alkali metal Highly reactive, Found in combined state, mostly as Salt.

Electrolyte Balance

Electrolyte Balance Electrolytes are a major component of body fluids. They enter the body in the food we eat and the beverages we drink. Electrolytes leave the body mainly through the kidneys by way of the urine, they also leave through the skin and feces. Severe vomiting and diarrhea can cause a loss of both water and electrolytes from the body, resulting in both water and electrolyte imbalances.

Electrolyte Balance The concentrations of electrolytes in body fluids must be maintained within specific limits, and even a small deviation outside these limits can have serious or life-threatening consequences. Three most clinically significant electrolytes are sodium ions, potassium ions, and calcium ions.

Fluid Movement Across the Cell Membrane One of the important functions of electrolytes, particularly sodium, is to control fluid movement between fluid compartments. The movement of fluid across the cell membrane differs from the movement of fluid between the interstitial compartment and plasma.

Sodium/Potassium Ion Pump The cell membrane acts as a barrier to separate intracellular and interstitial fluid compartments. Electrolytes move across the cell membrane through channels and ion pumps that are selective for specific ions. The sodium/potassium ion pump actively transports sodium and potassium.

Sodium/Potassium Ion Pump Ion pumps in the membrane help ions to move against their concentration gradient from an area of lower concentration to an area of higher concentration. These pumps require an input of energy in the form of ATP.

Sodium Ion Channel Channels specific for sodium ions allow these ions to diffuse from areas of higher to areas of lower concentration. In most cells the sodium channels don't allow sodium ions to move across the membrane very quickly.

Fluid Movement: Potassium Ion Channel The channels specific for potassium ions allow these ions to move across the membrane fairly quickly from areas of higher to areas of lower concentration. Differences in ion concentration between intracellular and interstitial fluids are caused by these selective ion channels and ion pumps in the cell membrane. These differences make the membrane potential possible and they facilitate a number of important physiological processes.

Fluid Movement: Water The cell membrane is freely permeable to water, which moves from the area of higher water concentration to lower water concentration.

Dietary sources In all foods even water. Table salt “NaCl”, added to food Bread, Cheese, salad, egg, nuts, spinach whole grain In all foods even water. 2.5 grams of salt contain 1gm of Na

REQUIREMENT Estimated safe and adequate daily dietary intake Infants 0 – 0.5 yrs 115 – 350mg 0.5 – 1.0yr 250 – 750mg Children 1 – 3 yrs 325 – 975 4 – 6 yrs 450 – 1350 7 – 10 yrs 600 – 1800 11+ 900 – 2700 Adults 1100 – 3300

Infants requirement is low because of Small lean body mass Composition of feces Cutaneous losses Minimum requirement for infants and young children is about 58 mg/day.

Human milk contains about 160mg/litre Cows milk contains about 483mg/litre

Absorption and Metabolism Sodium is readily absorbed from ileum Very little is excreted in feces except in diarrhea

Sweat is another major route of Sodium loss 20-50mg/L

Adults maintain sodium balance with very little intake Kidneys maintain its balance in blood (Homeostasis) under the influence of a hormone “Aldosterone” on renal tubules. When intake is decreased, aldosterone secretion Increases resulting in decrease of urinary excretion of sodium.

Distribution in the body Total body content = 3800 – 4000 meqt (165 – 174 mg) 44 % is in ECF = 1750 meqt (76 mg) (osmoticaly active, water soluble and exchangeable) 10 % is Soft tissues = 400 meqt (17.4 mg) 46 % is in Bone = 1850 meqt (80 mg)

Distribution in body / tissue Whole blood = 70 meqt/L (161 mg/dl) Plasma = 143 meqt/L (330 mg/dl) Cells = 37 meqt/L (85 mg/dl) Muscle tissue = 26 – 70 meqt/L (60 – 160 mg/dl) Nerve tissue = ~ 140 meqt/L (312 mg/dl)

Functions As a major cation of ECF It regulates Acid base balance, in conjunction with Cl / HCO3 It maintains the osmotic pressure of body fluids and protects severe fluid loss from body. It preserves normal irritability of muscle and permeability of cells.

Deficiency Diseases or Symptom When on normal diet  No hyponatermia Normal range in plasma is 135 – 145 meqt/L Hyponatermia is mostly secondary to Injury Illness (G/E) Burns Use of diuretics

Deficiency Diseases or Symptom Adrencorcortical insufficiency (Addison’s disease) Chronic Renal disease resulting in poor re-absorption of sodium Cirrhosis / CCF –  serum sodium level, without reduction in total body content of Na.

fall in tonicity as well as total volume of plasma Leading to Severe deficiency results in fall in tonicity as well as total volume of plasma Leading to Muscular cramps  Extremities and abdomen Headache Nausea Dry skin Reduce sweating Low urine out put having high specific gravity.

These are the conditions When Kidneys respond Complete re-absorption of filtered sodium Sodium excretion may fall to 20 meqt. / day or less.

Serum Sodium and adrenocortical function: Hypo-adrenalism 113 meq/L (Addison’s disease) Hyper-adrenalism 150 meq/L (Cushing syndrome) Normal 135 – 145 meq/L

Toxicity Diseases or Symptoms Hyper natremia may occur as a result of Rapid administration of sodium salt Hyper active adrenal cortex Administration of Cortisone or deoxy cortisone Dehydration excessive loss of water (Diabetes insipidus) May cause rise in blood pressure in susceptible individually.

Hypernatremia Let’s consider what will happen if the sodium concentration of the blood plasma increases?. What effect would this increase in sodium concentration have on the cells that are bathed by the interstitial fluid? ___ Cells swell ___ Cells shrink

Sodium Homeostasis The normal concentration range of sodium in the plasma is 136 - 145 milliequivalents per liter, making sodium the ion with the most significant osmotic effect in the extracellular fluid.

Hyponatremia What effect would this decrease in sodium concentration have on the cells that are bathed by the interstitial fluid? ___ Cells swell ___ Cells shrink

Roles of Sodium in the Body In addition to playing a pivotal role in nerve impulse conduction and muscle contraction, as the major extra cellular positive ion, sodium is the primary regulator of water movement in the body because water follows sodium by osmosis. If sodium levels in the plasma change, those changes determine fluid levels in the other compartments.

Renin-Angiotensin System angiotensinogen renin angiotensin I converting enzyme angiotensin II efferent constriction; PT reabsorption vasoconstriction aldosterone; CD reabsorption