1.1 Daily Intake and Loss of Water

• What are the two major sources of water intake in the body?

  Ingested liquids and synthesized water
• How much water is normally added to the body daily from ingestion?

  About 2100 ml/day
• How much water is synthesized in the body daily by oxidation of carbohydrates?

  About 200 ml/day
• What is the total daily water intake for the body?

  About 2300 ml/day
• What factors influence the variability of water intake among individuals?

  Climate, habits, and physical activity level
• What is insensible water loss?

  Water loss not consciously regulated
• How much water is lost daily through insensible water loss?

  About 700 ml/day
• Why is insensible water loss termed 'insensible'?

  Because it occurs without conscious awareness
• How much water is lost through the skin by diffusion?

  About 300 to 400 ml/day
• What minimizes water loss through the skin?

  The cholesterol-filled cornified layer
• How does extensive burns affect water loss through the skin?

  Increases evaporation rate up to 10-fold
• What is the average water loss through the respiratory tract?

  About 300 to 400 ml/day
• How does cold weather affect water loss through respiration?

  Increases water loss due to lower vapor pressure
• What is the normal volume of sweat lost daily?

  About 100 ml/day
• How can sweating affect fluid loss during exercise?

  Can increase to 1 to 2 L/hour
• Why is it important to increase water intake during heavy sweating?

  To prevent rapid depletion of body fluids
• How much water is normally lost in feces daily?

  About 100 ml/day
• What can happen to water loss in feces during severe diarrhea?

  Can increase to several liters a day
• What is the primary method by which the body maintains water balance?

  Controlling urine excretion by the kidneys
• What can urine volume range from in a dehydrated person?

  As low as 0.5 L/day
• What can urine volume reach in someone drinking excessive water?

  As high as 20 L/day
• How do kidneys adjust water and electrolyte excretion?

  By matching excretion rates to intake
• What is the variability of sodium intake among individuals?

  20 to 500 mEq/day
• What is the role of kidneys in fluid and electrolyte balance?

  Adjust excretion rates to match intake
• What are the mechanisms of daily water intake and loss?

  • Daily water intake:
  • Ingested liquids: ~2100 ml/day
  • Synthesized from carbohydrates: ~200 ml/day
  • Daily water loss:
  • Insensible loss: ~700 ml/day
  • Sweat: ~100 ml/day (up to 1-2 L/hour in heat)
  • Feces: ~100 ml/day (more in diarrhea)
  • Urine: variable (0.5 to 20 L/day)
• What are the factors affecting water loss in the body?

  • Insensible water loss: evaporation from skin and lungs
  • Sweat: varies with activity and temperature
  • Feces: small under normal conditions, increases in diarrhea
  • Urine: regulated by kidneys based on intake and needs
• What are the consequences of severe diarrhea on water balance?

  • Significant increase in fecal water loss
  • Risk of dehydration and life-threatening conditions
  • Requires prompt correction of fluid loss
• How do kidneys maintain electrolyte balance?

  • Adjust excretion rates of sodium, chloride, potassium
  • Compensate for excessive losses in disease states
  • Maintain overall fluid and electrolyte homeostasis