Fluid Balance and Body Compartments

Fluid Compartments and Balance

• About two-thirds of the body's fluid is contained in the intracellular compartment.
• Interstitial fluid makes up approximately 80% of the extracellular fluid.
• Water primarily moves in and out of body compartments through osmosis.
• The main determinant of fluid balance is the concentration of solutes in various compartments.
• Most solutes in body fluids are electrolytes, such as sodium and potassium.

Body Constituents and Regulation

• The largest single constituent in the body is water, accounting for a significant portion of body weight.
• The urge to drink is regulated by the hypothalamus, which responds to changes in blood osmolarity.
• Hormones that regulate urine production include antidiuretic hormone (ADH) and aldosterone.
• The primary method to regulate body water balance is through renal function and fluid intake.
• Fluid balance implies maintaining equilibrium between intake and output of fluids in the body.

Acid-Base Disorders

• Respiratory alkalosis is characterized by decreased arterial blood carbon dioxide and increased pH.
• Metabolic acidosis is caused by increased production of acids or decreased bicarbonate levels.
• Metabolic alkalosis is often a result of excessive loss of acids or an increase in bicarbonate concentration.
• Increased bicarbonate concentration is characteristic of metabolic alkalosis.
• Respiratory alkalosis can arise from conditions causing hyperventilation.
• Respiratory acidosis is characterized by increased carbon dioxide and decreased pH, often due to hypoventilation.

Electrolyte Functions and Roles

• The most abundant extracellular ion is sodium, crucial for fluid balance and nerve impulses.
• Chloride plays a role in regulating osmotic pressure and is essential for forming hydrochloric acid in the stomach.
• Potassium is the most abundant cation in intracellular fluid, pivotal in fluid volume maintenance, impulse conduction, and muscle contraction.
• Calcium, primarily an extracellular ion, is important for blood coagulation, neurotransmitter release, and muscle excitability.

Buffer Systems

• The most abundant buffer in body cells and plasma is the protein buffer system.
• The bicarbonate buffer system plays a critical role in regulating blood pH.
• The phosphate buffer system is significant in maintaining pH in red blood cells and kidney tubular fluids.

Clinical Conditions

• Respiratory acidosis is caused by hypoventilation, leading to elevated carbon dioxide and decreased pH.
• Alkalosis conditions are characterized by elevated blood pH (above 7.45) and can lead to central nervous system overexcitability due to synaptic transmission facilitation.