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Understanding Dehydration: Impacts & Prevention

Explore effects of long-term exposure to hot & dry environments on fluid intake/output. Learn about body fluid compartments, osmolarity, types of dehydration, and importance of maintaining electrolyte balance. Discover the causes, clinical features, and management of dehydration in different populations. Gain insights into the osmoreceptor-ADH feedback system controlling thirst and fluid intake. Stay informed to prevent dehydration in various scenarios.

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Understanding Dehydration: Impacts & Prevention

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  1. Dehydration Effects of long-term exposure to hot and dry environment Layla Abdulla Physiology – Group 3

  2. Outline

  3. Fluid intake and output • Total body water is ≈ 60% of body weight- age, adipose tissue, gender • Daily water intake- in liquids, food, or oxidation of carbohydrates- depends on climate, habits, level of physical activity • Daily water loss- insensible water loss- fluid loss in sweat- water lost in feces- water lost by kidneys

  4. Water loss by kidneys • Occurs in form of urine excreted by kidneys • Most important way body maintains balance of: - water intake & output- electrolyte intake & output • Urine volume:- dehydration: 0.5L/day - drinking  amounts of water: 20L/day • Kidneys adjust excretion rate of water andelectrolytes: - to precisely match intake of the substances- to compensate for excessive losses

  5. Fluid intake and output

  6. Body fluid compartments • Intracellular fluid:- K+, Mg2+, ATP, ADP, AMP • Extracellular fluid:- Na+, Cl-, HCO3- • Transcellular fluid:- cerebrospinal, pleural, peritoneal, digestive fluids

  7. Water shifts between compartments • Volume of body fluid compartment depends on amount of solute it contains. • Osmolarity: concentration of solute particles, expressed as osmoles (or milliosmoles) per liter of solution. • In steady state, intracellular osmolarity =extracellular osmolarity. • NaCl, NaHCO3, mannitol confined to ECFcompartment because they don’t readily crosscell membranes. To maintain this equality, water shifts freely + rapidlyacross cell membranes.

  8. Dehydration • Decrease in ECF volume – water loss, Na+ loss • Tonicity: effect of concentration of solution on volume of cell- Isotonic (solution doesn’t change volume)- Hypotonic (solution causes cell to swell)- Hypertonic (solution causes cell to shrink) • Types:- Isosmotic dehydration (hemorrhage, gastrointestinal fluid loss)- Hyposmotic dehydration (renal loss of NaCl)- Hyperosmotic dehydration (water deficit)

  9. Dehydration Primary measurement is plasma sodium concentration • Normal plasma sodium concentration is ≈ 142 mEq/L • Hypernatremia = if sodium concentration is elevated above 155 mmol/L

  10. Dehydration - hypernatremia • Associated with  plasma sodium concentration,which causes increased osmolarity • Causes: - water loss which concentrates sodium ions- excess sodium in extracellular fluid- decreased ADH effect, renal causes • Clinical features:- abnormal urine output, ECF volume is lowered, CNS disorders

  11. Dehydration - hypernatremia

  12. Dehydration - hypernatremia • When water intake that is less than water loss- Prolonged, heavy exercise- Lost in the desert without adequate drinking water • Sweat = loss of NaCl and water- compared to body fluids, sweat has  water than solute • In new steady state,  ECF and ICF volumes,  ECF & ICF osmolarities

  13. Dehydration - hypernatremia • Even a small rise in plasma Na+ concentration above normal range results in sensation of thirst and correction of abnormality by increase in free water intake • So hypernatremia occurs most often in- infants, elderly- people with impared mental status- people with impaired sense of thirst- people who have intact thirst mechanism but unable to obtain water • During water deficits, kidneys minimize fluid loss through osmoreceptor-ADH feedback systemand increase adequate fluid intake through thirst mechanism.

  14. Osmoreceptor-ADH Feedback System

  15. Thirst • Thirst = conscious desire for water • Many factors that stimulate ADH secretion also  thirst. • Temporarily relieved after drinking water to prevent overhydration and excess dilution of body fluids

  16. Sources • Hall, John E., and Arthur C. Guyton. Guyton and Hall Textbook of Medical Physiology.Philadelphia, PA: Saunders/Elsevier, 2011. Print. • Costanzo, Linda S. Physiology with Student Consult Online Access. 5th ed. Philadelphia, PA: Saunders Elsevier, 2014. Print. • Costanzo, Linda S. Board Review Series Physiology. 5th ed. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2011. Print.

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