Water Balance and Body Fluids Quiz

Water Balance

• Water movement in the body is primarily regulated by osmosis which is the movement of water molecules through a semi-permeable membrane from an area of high water concentration to low water concentration.
• Concentration of solutes in body fluids determines the direction of water movement.
• Osmoreceptors in the hypothalamus detect changes in blood osmotic pressure (concentration of solutes in the blood), triggering thirst.
• Electrolytes are inorganic compounds that dissociate into ions in solution, playing a crucial role in body fluid balance.
• "Where sodium goes, water follows" highlights the strong influence of sodium on water distribution.

Body Water Content

• The average adult human body contains 40 liters of water, approximately 10.56 gallons.
• Body water content varies by age and gender: babies have the highest proportion (75%), men have around 63%, and women 52%.

Fluid Compartments

• Body fluids are divided into intracellular and extracellular compartments separated by selectively permeable membranes.
• Intracellular fluid makes up 2/3 (63%) of the total body water and is found within cells.
• Extracellular fluid constitutes 1/3 (37%) of total body water and is divided into interstitial fluid (80%) and blood plasma (20%).

Composition of Body Fluids

• Extracellular fluids are characterized by high concentrations of sodium (Na+), chloride (Cl-), calcium (Ca++), and bicarbonate (HCO3-).
• Blood plasma contains higher protein levels compared to interstitial fluid and lymph.
• Intracellular fluids have high concentrations of potassium (K+), phosphate, magnesium (Mg++), and more protein than plasma.

Regulation of Water Intake

• Thirst is the primary mechanism for regulating water intake.
• Even a 1% decrease in body water triggers dehydration, resulting in:
  • Reduced saliva production
  • Increased blood osmotic pressure, stimulating osmoreceptors in the hypothalamus
  • Decreased blood volume leading to the release of renin

Regulation of Water Output

• Water output is primarily regulated through urine formation by the kidneys.
• Antidiuretic hormone (ADH) is released in response to increased blood tonicity or decreased blood volume.
  • ADH acts on the distal convoluted tubules and collecting ducts of the kidneys, increasing water reabsorption.
• Aldosterone, stimulated by angiotensin II (produced due to renin release), promotes sodium (and water) reabsorption in the kidneys.
• Atrial natriuretic peptide (ANP) is released when pressure in the right atrium is too high, causing sodium (and water) loss.

Water Imbalances

• Dehydration is the most common water imbalance, occurring due to:
  • Prolonged diarrhea or vomiting
  • Excessive sweating