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Effects of long-term exposure to hot and dry environment

Dehydration. Effects of long-term exposure to hot and dry environment. Layla Abdulla Physiology – Group 3. Outline. Fluid intake and output. Total body water is ≈ 60% of body weight - age, adipose tissue, gender

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Effects of long-term exposure to hot and dry environment

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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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