Sodium — Functions & Management

A Wonder Electrolyte

INTRODUCTION

Human body fluids contain cells, electrolytes, minerals, water and other compounds. All these components have a crucial role in supplying nutrients to the target body organ through various processes like diffusion, osmosis, filtration and active transport. The electrolytes present in the ECF & ICF include sodium, potassium and chloride. Today we are discussing the most abundant electrolyte in extracellular fluid and its role in human body functioning.

WHAT IS SODIUM ??

Sodium is a positively charged ion which can conduct electricity. It is an active element and reacts with almost everything it comes in contact with. When reacted with chlorine, a volatile reaction occurs. When the reaction settles down, the leftover is neither reactive nor poisonous. This substance is called sodium chloride also known as table salt.

ROLE OF SODIUM IN HUMAN BODY

The important human body systems like circulation, respiration, elimination depend on sodium balance. Sodium derived from salt has an important role in the transmission of nerve impulse and muscle contraction. Listed below are some other important functions of sodium.

• Maintains blood volume and blood pressure
• Influences the permeability of cell membrane and helps to move the substances across the cell membrane
• Regulates acid base balance by attaching to chloride and bicarbonate
• Plays an important role in intracellular chemical reactions
• Helps generation of electric signals in the nervous system

SOURCES OF SODIUM

Apart from saliva and bile, body fluids like gastric, pancreatic and intestinal secretions also contain sodium. The normal serum sodium level is 135–145 mEq/L. The excess sodium is excreted through urine, feces and perspiration. People who sweat a lot due to workouts or hot weather, lose more sodium along with body fluids and become dehydrated. Some common sources which can replenish your body with sodium are canned food, processed products, cured meat, seafood, cheese, cottage cheese, pickles, salted pretzels, potato chips, table salt and bread. Fresh fruits and vegetables have less amount of sodium. Talk to your dietician and learn more about recommended dietary allowances and various food sources to avoid sodium imbalance and related complications.

COMPLICATIONS

Generally, during abnormal sodium intake, the kidney regulates the fluid volume to either preserve the available sodium or eliminate the excess sodium. In certain conditions, when kidneys are unable to excrete the excess sodium, the body retains water to dilute it. The increase in fluid volume due to water retention, raises the blood volume. This entire mechanism finally leads to high blood pressure as the heart begins to work harder to pump this larger blood volume.

Complications associated with abnormal serum sodium levels can be monitored and treated with medication, dietary modifications and lifestyle changes. Dehydration, headache, nausea, muscle weakness, fatigue are some of the common signs. Consult your doctor to get your treatment started.

• HYPERNATREMIA

A serum sodium level higher than 145 mEq/L is called hypernatremia. It is usually caused by increased sodium intake or water loss. Other possible causes can be diabetes mellitus , hyperaldosteronism, and cushing’s syndrome. Hypernateremia can make serum hypertonic ( concentrated)

• EDEMA

Edema is the accumulation of fluids intracellularly or extracellularly. One possible cause of edema is salt and water retention. Edema can be detected by a simple finger test. Make a depression on the pre tibial region with a finger for 5 seconds. After releasing the finger, the presence of a pit or an indentation indicates edema. Swelling without pitting is called non pitting edema.

• HYPONATREMIA

A serum sodium level below 135 mEQ/L is called hyponatremia. Lower intake of dietary sodium or excess excretion of sodium leads to hyponatremia. Patients who are on a sodium restricted diet or those who have conditions like excess sweating, lower aldosterone levels or renal disorder can have hyponatremia.

Other conditions like hyperglycemia, hyperlipidemia, hyperproteinemia also affect the serum sodium concentration. Increased availability of the particles such as glucose, lipids or proteins decreases the water availability in which sodium dissolves resulting in lower sodium levels. Also, with higher glucose level, renal tubular flow increases which causes further sodium loss.

SODIUM BALANCE

Human body has several physiological mechanisms to maintain the sodium balance. These naturally occurring mechanisms aim to protect our body from complications associated with the serum sodium level. Here is a brief explanation of each mechanism.

• THIRST MECHANISM

Due to high sodium levels the osmolality (concentration of a solution) of fluid increases which triggers nerve impulse to the brain and causes thirst. Intake of water increases the volume of ECF and normalizes the osmolality.

• ANTIDIURETIC HORMONE

Hypothalamus stimulates the pituitary gland to release ADH into the bloodstream (Antidiuretic hormone also called vasopressin, and is synthesized by hypothalamus. The primary roles of ADH are maintaining osmotic balance, sodium homeostasis and blood pressure regulation) This causes the kidney to retain water, diluting the serum sodium level.

• GLOMERULAR FILTRATION RATE

Higher concentration of sodium increases the blood volume. Greater blood volume increases the hydrostatic pressure which pushes the fluid out of glomerular capillaries in the kidney.This leads to increased GFR, excretion of ECF through urine and flushing of excess sodium.

• RENIN ANGIOTENSIN MECHANISM

When a greater amount of sodium is ingested through diet, the kidney signals juxtaglomerular cells to secrete less renin causing reduction in vasoconstriction (constriction of blood vessels). This factor is important in controlling blood pressure which rises with increase in ECF volume.

• ATRIAL NATRIURETIC PEPTIDE

High sodium intake increases the fluid volume. This leads to stretching of atrial walls and release of ANP into the blood. This process suppresses the effect of aldosterone in the kidneys causing lower sodium reabsorption and increased sodium excretion through urine.

• OSMOTIC PRESSURE

Due to osmosis, water in the cells moves to ECF resulting in dilution. Unfortunately this mechanism can cause cellular dehydration.

• SODIUM POTASSIUM PUMP

The intracellular sodium concentration is low whereas potassium level is high. These ions tend to move from high concentration to low concentration. Which means sodium will tend to move into the cell and potassium ions into the ecf. The sodium potassium pump prevents this diffusion by connecting these ions with a carrier that accompanies these ions through the cell wall against the concentration gradient. This process of using membrane pump is called active transport.

REFERENCE

Chernecky C. Chernecky, Denise Macklin, & Kathleen Murphy- ende, (2001). Fluids & Electrolytes. (1 ed.). Philadelphia :Saunders.

American heart association (2013). Eat Less Salt. (1 ed.). New York: Clarkson Potter.