Human Body Water Composition
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Questions and Answers

What percentage of body weight is water in men?

  • Seventy percent
  • Fifty five percent
  • Sixty percent (correct)
  • Sixty six percent

    • What percentage of total body water is in the plasma?

  • Eighty percent
  • Eight percent (correct)
  • Thirty three percent
  • Sixty six percent

    • What is the primary determinant of water distribution in the body?

  • Energy availability
  • Diffusion rates
  • Osmotic content of the ICF and ECF (correct)
  • Sodium pump activity

    • What is the concentration of potassium in the intracellular fluid?

    <p>110 mmol/l</p> Signup and view all the answers

    What is the concentration of sodium in the extracellular fluid?

    <p>135 mmol/l</p> Signup and view all the answers

    What is the term for the equal osmotic concentrations of the ICF and ECF?

    <p>Isotonic</p> Signup and view all the answers

    What percentage of body water is in the extracellular fluid?

    <p>Thirty three percent</p> Signup and view all the answers

    What is the primary mechanism of water transport in the body?

    <p>Free permeability</p> Signup and view all the answers

    What is the normal range of osmolality of the ECF?

    <p>282-295 mmol/kg of water</p> Signup and view all the answers

    What happens to the ECF osmolality when there is water deprivation?

    <p>It increases</p> Signup and view all the answers

    What is the function of vasopressin in the body?

    <p>To make the renal collecting ducts permeable to water</p> Signup and view all the answers

    What is the maximum urine concentration that can be achieved in humans?

    <p>1200 mmol/l</p> Signup and view all the answers

    What happens to water in the ICF when ECF osmolality increases?

    <p>It moves to the ECF</p> Signup and view all the answers

    What is the result of stimulating the hypothalamic thirst center?

    <p>Increased water intake</p> Signup and view all the answers

    What is the effect of vasopressin on the renal collecting ducts?

    <p>It makes them permeable to water</p> Signup and view all the answers

    What is the outcome of restoring ECF osmolality?

    <p>Renal water retention</p> Signup and view all the answers

    What is the minimum daily water intake necessary for the maintenance of water balance?

    <p>1100 ml</p> Signup and view all the answers

    What is the normal ECF sodium concentration?

    <p>135-145 mmol/l</p> Signup and view all the answers

    What is the normal daily intake of sodium in the western world?

    <p>100-200 mmol/day</p> Signup and view all the answers

    What is the obligatory sodium loss via the kidneys, skin and gut?

    <p>Less than 10 mmol/day</p> Signup and view all the answers

    What is the rate of sodium secretion into the gut?

    <p>1000 mmol/day</p> Signup and view all the answers

    What is the rate of sodium filtration by the kidneys?

    <p>25000 mmol/day</p> Signup and view all the answers

    What percentage of the body's sodium is freely exchangeable?

    <p>70%</p> Signup and view all the answers

    What is the consequences of a partial failure of sodium reabsorption?

    <p>Sodium homeostasis will be compromised</p> Signup and view all the answers

    What is the minimum change in osmolality that osmoreceptors can detect?

    <p>1%</p> Signup and view all the answers

    What is the plasma osmolality level at which vasopressin becomes detectable in the plasma?

    <p>280 mmol/kg</p> Signup and view all the answers

    What happens to vasopressin secretion when the ECF osmolality falls?

    <p>It is inhibited</p> Signup and view all the answers

    What type of solute can diffuse readily across cell membranes and increase ICF osmolality?

    <p>Urea</p> Signup and view all the answers

    What happens to vasopressin secretion when there is a decrease in plasma volume of more than 10%?

    <p>It increases</p> Signup and view all the answers

    What is the primary stimulus for vasopressin release when there is a decrease in plasma volume?

    <p>Hypovolemia</p> Signup and view all the answers

    What is the result of vasopressin secretion when ECF osmolality increases?

    <p>Concentrated urine production</p> Signup and view all the answers

    What type of receptors besides osmoreceptors affect vasopressin secretion?

    <p>Baroreceptors and volume receptors</p> Signup and view all the answers

    Which of the following stimulates vasopressin secretion?

    <p>Increased ECF osmolality</p> Signup and view all the answers

    What is the result of severe water depletion on the brain?

    <p>Cerebral dehydration</p> Signup and view all the answers

    How should water be given to a patient with water depletion?

    <p>Orally or via nasogastric tube</p> Signup and view all the answers

    What is the goal of fluid replacement in water depletion?

    <p>Correct approximately two-thirds of the deficit in the first 24 hours</p> Signup and view all the answers

    What is the effect of water depletion on ECF osmolality?

    <p>Increased ECF osmolality</p> Signup and view all the answers

    Which of the following inhibits vasopressin secretion?

    <p>Alcohol</p> Signup and view all the answers

    What is the result of rapid fluid replacement in severe water depletion?

    <p>Cerebral oedema</p> Signup and view all the answers

    Which of the following stimulates the thirst center?

    <p>Increased ECF osmolality</p> Signup and view all the answers

    Study Notes

    Water Distribution

    • Water accounts for approximately 60% of body weight in men and 55% in women, with 66% of this water being in the intracellular fluid (ICF) and 33% in the extracellular fluids (ECF)
    • Only 8% of total body water is in the plasma

    Sodium Distribution

    • The body of an adult man contains approximately 3000 mmol of sodium, with 70% of it being freely exchangeable and the remainder complexed in bone
    • Most cell membranes are permeable to sodium, which is maintained by active pumping of sodium from ICF to ECF by Na+-K+ ATPase

    Water and Sodium Homeostasis

    • The minimum daily water intake necessary for the maintenance of water balance is approximately 1100 ml, which increases if losses are abnormally large
    • Sodium input and output are normally balanced, with the kidneys filtering 25,000 mmol/day and the vast majority being regained by reabsorption in the gut and renal tubule
    • Excessive sodium intake can be harmful, such as in the pathogenesis of hypertension

    Osmolality and Vasopressin

    • Changes in body water content independent of the amount of solute will alter the osmolality, which is normally maintained in the range of 282-295 mmol/kg of water
    • A slight increase in ECF osmolality will stimulate the hypothalamic thirst center and osmoreceptors, which causes the release of vasopressin (antidiuretic hormone or ADH)
    • Vasopressin renders the renal collecting ducts permeable to water, permitting water reabsorption and concentration of the urine

    Physiological Responses to Water Loss

    • Water loss will increase ECF osmolality, stimulating vasopressin release and promoting water reabsorption
    • Redistribution of water from ICF to ECF will occur, increasing ECF volume and decreasing ICF volume
    • Renal water retention will occur, and increased water intake will help restore ECF osmolality to normal

    Vasopressin Secretion

    • Vasopressin concentration rises sharply if plasma osmolality increases above 282 mmol/kg
    • A small decrease in blood volume has little effect on vasopressin secretion, but a decrease in plasma volume of more than 10% will stimulate vasopressin release
    • Other stimuli affecting vasopressin secretion include angiotensin II, arterial and venous baroreceptors, and volume receptors

    Water Depletion

    • Water depletion will occur if water intake is inadequate or losses are excessive
    • Loss of water from ECF causes an increase in osmolality, stimulating thirst and vasopressin secretion
    • Severe water depletion can cause cerebral dehydration, which may lead to cerebral hemorrhage or oedema

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    Description

    Learn about the distribution of water in the human body, including its composition in men and women, and the percentage of water in intracellular and extracellular fluids.

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