10. WATER AND ELECTROLYTES

Water and Electrolytes

Water and electrolytes are essential for maintaining life. They help regulate body temperature, support organ function, maintain fluid balance and allow biochemical reactions to occur. This note explains the distribution of water, functions, electrolyte balance, dehydration and oral rehydration therapy (ORT) in simple language for D.Pharmacy students.

Water and Electrolytes: Distribution, Functions, Balance, Dehydration and ORS Therapy

Water and electrolytes are essential for maintaining life. They help regulate body temperature, support organ function, maintain fluid balance and allow biochemical reactions to occur. This note explains the distribution of water, functions, electrolyte balance, dehydration and oral rehydration therapy (ORT).

Distribution of Water in the Body

Water makes up about 60% of the total body weight in adults. It is distributed into different compartments:

1. Intracellular Fluid (ICF)

Water inside the cells. It forms about 40% of body weight (two-thirds of total body water).

2. Extracellular Fluid (ECF)

Water outside the cells. It forms about 20% of body weight and is divided into:

• Interstitial fluid: Fluid between tissues.
• Plasma: Fluid portion of blood.
• Transcellular fluids: CSF, synovial fluid, digestive juices, etc.

Functions of Water in the Body

Water performs several critical roles in the body.

• Regulates body temperature: Helps in sweating and cooling.
• Medium for biochemical reactions: Most metabolic activities occur in water.
• Transport of nutrients and waste: Blood (mostly water) carries oxygen and nutrients.
• Lubrication: Joints, eyes and tissues require water for smooth movement.
• Maintains blood volume and pressure.
• Helps digestion and absorption.

Water Turnover and Balance

Water Intake (Daily)

• Beverages: Drinking water, juice, tea.
• Food: Fruits, vegetables, cooked meals.
• Metabolic water: Formed during oxidation of carbohydrates, fats and proteins.

Water Loss (Daily)

• Urine
• Sweat
• Breathing (lungs)
• Feces

Water balance is achieved when intake equals loss. Hormones like ADH (antidiuretic hormone), aldosterone and thirst mechanism help maintain the balance.

Electrolyte Composition of Body Fluids

Electrolytes are minerals that carry electrical charges and help maintain fluid balance and nerve function.

Major Electrolytes in ECF (Extracellular Fluid)

• Sodium (Na⁺) – main extracellular cation
• Chloride (Cl⁻) – main extracellular anion
• Bicarbonate (HCO₃⁻) – helps maintain pH

Major Electrolytes in ICF (Intracellular Fluid)

• Potassium (K⁺) – main intracellular cation
• Phosphate (PO₄³⁻)
• Magnesium (Mg²⁺)

Dietary Intake of Electrolytes

• Sodium: 1500–2300 mg/day
• Potassium: 2600–3400 mg/day
• Chloride: 2300 mg/day
• Calcium: 1000–1200 mg/day
• Magnesium: 310–420 mg/day

Balanced intake is necessary for nerve conduction, muscle contraction, hydration and acid–base balance.

Electrolyte Balance

Proper balance of electrolytes is essential for:

• Maintaining fluid distribution between ICF and ECF
• Normal nerve and muscle function
• Maintaining pH and acid–base balance
• Regulating blood pressure and heart rhythm

Hormones such as aldosterone, ADH and natriuretic peptides control electrolyte levels in the body.

Dehydration

Dehydration occurs when the body loses more water and electrolytes than it takes in. It may be mild, moderate or severe depending on the degree of loss.

Causes of Dehydration

• Vomiting and diarrhea
• Excessive sweating (fever, exercise, heat exposure)
• Burns
• Reduced intake of water
• Increased urination (diabetes, diuretics)

Symptoms of Dehydration

• Dry mouth and skin
• Thirst
• Dizziness
• Low blood pressure
• Weak pulse
• Dark yellow urine
• In severe cases: confusion, shock

Oral Rehydration Therapy (ORT)

ORT is a simple and effective method to treat dehydration, especially due to diarrhea and vomiting. It replaces lost water, glucose and electrolytes.

Composition of ORS (WHO Standard)

• Glucose – 13.5 g
• Sodium chloride – 2.6 g
• Potassium chloride – 1.5 g
• Sodium citrate – 2.9 g
• Water – 1 liter

How ORS Works

The glucose–sodium co‑transport mechanism in the intestine helps the body absorb sodium and water quickly, even during severe diarrhea.

When to Use ORS

• Diarrhea
• Vomiting
• Heat exhaustion
• Mild to moderate dehydration

Summary:

Water and electrolytes are vital for life, supporting body temperature regulation, fluid balance, nerve and muscle function, and biochemical reactions. Proper distribution between ICF and ECF, along with adequate intake and hormonal control, keeps the body hydrated. Dehydration, often caused by vomiting, diarrhea, sweating or reduced intake, can be effectively treated with oral rehydration therapy (ORS), which replenishes water, glucose and electrolytes in a fixed, WHO‑recommended ratio. This concept is essential for D.Pharmacy students to understand fluid therapy and electrolyte management in clinical practice.

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