Water and Fluid Balance

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Water and Fluid Balance
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Water

• Greatest component of human body 50-70 of bodys
  weight (40 litres)
• Muscle 73 water
• Adipose tissue 20 water
• Cannot conserve water therefore only survive a
  few days without drinking

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Functions

• Intracellular and extracellular fluid
• Aids biochemical reactions
• Transport of nutrients, metabolites, waste
  products, hormones between cells in body
• Aids exchange of oxygen and carbon dioxide in the
  lungs

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Functions (2)

• Balances blood volume
• Temperature regulation
• Lubricates and cushions joints
• Basis of saliva, bile and amniotic fluid

5
Intra and extracellular fluid

• Water inside cells intracellular
• Water outside cells or in blood extra
• Body controls intra and extracellular fluids by
  controlling electrolyte concentrations
• Intra contains potassium
• Extra contains sodium

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How much do we need?

• Approx 3000ml men, 2200ml women per day
• 1000ml comes from food
• 300ml as byproduct of metabolism
• Rest from ingested fluids
• Test adequacy of intake using colour of urine,
  should be clear to pale yellow

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Water balance

• Tightly controlled
• If water volume drops body retains more water
• Dehydration-due to not drinking enough or losing
  too much
• More losses if hot, doing hard physical activity,
  during fever, vomiting and diarrhoea
• Water intoxication-too much water in body, rare,
  occurs if drink huge amount or kidneys not
  working properly

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Removal of waste products

• Urea, byproduct of protein metabolism, major body
  waste, is removed via the urine
• Excess sodium (salt) also excreted in urine
• Low urine output forces kidneys to produce very
  concentrated urine which increases risk of kidney
  stone formation esp among men
• Kidney stones are substances that have
  precipitated out of the urine and accumulated

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Water intake and output

• Intake
• Fluids 550-1500
• Food 700
• Metabolic200-300
• Total 1500-3000

• Output
• Evaporation from lungs 400-600
• Sweat 200
• Urine 500-1500
• Faeces 150
• Total 1500-3000

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Thirst

• Brain communicates need to drink by signaling
  thirst
• Not always reliable esp for infants, older
  people, and during vigorous exercise
• These groups need to take steps to prevent eg
  athletes need to monitor fluid intake before and
  after training/events

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Thirst

• Once thirsty, body releases two hormones to
  conserve water
• Hormone 1 - Kidneys reduce urine flow
• Decrease blood volume and blood pressure
• Hormone 2 - Kidney retains more sodium and thus
  more water
• Still some water loss eg skin, lungs
• Alcohol inhibits hormone 1 release for fluid
  conservation

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Dehydration

• Losses must be replaced
• 1-2 loss of body weight feel thirsty
• 4 loss muscles lose strength, endurance
• 10-12 heat tolerance decreased, weakness
• 20 - coma and death can follow

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Water content of food

• Tomato 94
• Milk 88
• Egg 75
• Bread 45
• Muesli 10
• Peanuts 5

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Sources of fluid

• Water
• Milk
• Caffeinated drinks
• Fruit juices, soft drinks, cordials and sports
  drinks

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Water

• Town supply water (may contain fluoride-beneficial
  to prevent tooth decay)
• Safety of supply may be issue
• No known benefits of bottled
• water compared to tap water

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Milk

• Important source of calcium, protein and other
  nutrients
• Choose reduced and low fat varieties
• Fortified soy beverages are suitable replacement

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Caffeinated drinks

• Coffee, tea, cocoa, cola flavoured drinks contain
  caffeine
• Also energy drinks containing guarana or cola nut
• Caffeine is stimulant and mild diuretic
• Tea, coffee and soft drinks are most frequently
  consumed drinks in NZ
• Addition of sugar to tea/coffee adds energy to
  diet

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Fruit juices, soft drinks etc

• Contain water, some have Vit C, energy
• Contribute to excess energy consumption
• Contribute to dental decay eg phosphoric acid and
  citric acid in sports drinks can erode enamel
• Frequency of intake adds to these problems

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Energy and sugar content of drinks

• Drink Amount kcal sugar/g
• Gatorade 1 cup 74 16.3
• Lucozade 1 cup 164 37
• Powerade 1 cup 76 18
• V drink 250mls 95 23.5
• Juice 1 cup 115 25.1
• Coke 355mls 161 39.8

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Practical advice

• Drink plenty of water
• Take in fluid 6-8 glasses per day
• Sometimes choose low fat milk as alternative to
  water or soft drinks
• Limit fruit juice, cordial, energy and soft
  drinks esp for children due to energy content
• Coffee-5 cups per day Heart Foundation

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Electrolytes

• Compounds that dissociate into ve or ve charge
  ions when dissolved in water
• Sodium (Na)- major cation in ECF
• Sweat has small amount of Na in it
• Regulates size of ECF
• Controls nerve impulses and muscle contractions
• Table salt, protein foods, occurs naturally in
  fruits and vegetables, breads and cereals, dairy
  products
• 90-95 of Na is lost in urine, rest in feces and
  sweat
• RDI
• 0-5 mths 120mg/day - 6-11 mths 200mg/day
• 1 yr old 225mg/day - 2-5 yrs old 300mg/day
• 6-9 yrs old 400mg/day - 10-18 yrs 500mg/day
• gt18 yrs old 500mg/day

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Chloride (cl)

• Principle anion (-ve charge) of ECF
• Together with Na maintains body water balance
• Together with phosphate, sulfate, helps to
  maintain acid-base balance in body fluids
• Ingested through table salt, chlorine in water
  (minimal)
• Excreted in urine and sweat

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Potassium (k)

• Major cation of ICF
• Present in small amounts in ECF
• K promotes cellular growth
• K content of muscle is related to muscle mass and
  glycogen storage, therefore adequate supply is
  essential if muscle is being formed.
• Together with Na- maintains normal water balance,
  osmotic equilibrium and acid-base balance.
• Together with Calcium regulates neuromuscular
  activity
• Dairy products, fish and shellfish, fruits and
  vegetables breads and cereals
• 90 excreted in urine, rest lost in feces
• RDI 1.6-2g /day