Body Fluids Composition and Functions

Body Fluids

• Fluids make up approximately 60% of the adult human body, primarily composed of water and ions.
• Body fluids are divided into two main compartments: intracellular fluid (ICF) and extracellular fluid (ECF).
• ICF makes up two-thirds of the body's water, while ECF makes up one-third.
• ICF functions as a stabilizing agent, maintains cell shape, and assists with transport of nutrients across the cell membrane.
• ECF appears as interstitial tissue fluid and intravascular fluid.

Functions of Water

• Acts as a solvent for cellular components.
• Has catalytic action, accelerating chemical reactions in the body.
• Provides lubricating actions, preventing friction in joints and other areas.
• Regulates heat loss through evaporation from skin and lungs and removal in urine.

Fluid and Electrolyte Balance

• Fluid and electrolyte balance is a dynamic process crucial for life and homeostasis.
• Homeostasis is maintained by the endocrine system and nervous system.
• Sources of water to the body include dietary liquids, solid foods, and oxidation of foodstuffs.
• Water output occurs through urine, respiration, lactation, feces, tears, and evaporation from skin and lungs.

Normal Intake and Output

• Daily intake: approximately 2,500 ml of fluid.
• Levels of intake: fluids (1,200 ml), foods (1,000 ml), and metabolic products (30 ml).
• Daily output should be approximately equal to intake.

Overhydration and Dehydration

• Overhydration: occurs when too much water is taken without solute, leading to decreased plasma osmolarity.
• Water intoxication: occurs when excessive amounts of water, low-sodium, or hypotonic solutions are taken.
• Dehydration: occurs when water is lost without solute, leading to increased plasma osmolarity.
• Treatment of dehydration: supplemental fluids and electrolytes are often administered.

Fluid Regulation Mechanisms

• Thirst center: regulates the desire to drink.
• Antidiuretic hormone (ADH): controls blood pressure, blood volume, and tissue water content.
• Renin-angiotensin system (RAA): controls fluid volume by regulating blood flow to the renal juxtaglomerular apparatus.
• Atrial natriuretic peptide (ANP): released by the heart to correct overload imbalances.

Electrolytes

• Electrolytes: substances that dissociate into ions when dissolved in water, making up 7% of total body weight.
• Functions of electrolytes:
  • Maintain acid-base balance.
  • Maintain normal osmolality and volume of body fluid.
  • Regulate nerve and muscle function.
  • Help rebuild damaged tissue.
• Electrolytes are found in the form of inorganic salts, acids, and bases.
• Electrolyte concentrations are measured according to their chemical activity and expressed as milliequivalents.

Intracellular and Extracellular Electrolytes

• Intracellular electrolytes: potassium, magnesium, sulfate, phosphate, and others.
• Extracellular electrolytes: sodium, chlorine, calcium, bicarbonate, and others.

Electrolyte Imbalance

• Causes:
  • Kidney damage caused by illness, such as diabetes or high blood pressure.
  • Severe vomiting, diarrhea, GI malabsorption.
  • Lifestyle factors, such as drinking too much water and eating poorly.
  • Inherited genetic conditions.
• Types of electrolyte disorders:
  • Hyper (too high).
  • Hypo (too low).