Transcript Chapter 6 Digestion, Absorption, and Metabolism

Chapter 8
Water and
Electrolytes:
Striking a Balance
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Laney College
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A Water Molecule
• Inorganic (no carbon)
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Water’s Charge Distribution
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A Water Molecule
• Water has unique bonding properties than in
other substances.
– Hydrogen side has a slight positive charge
– Oxygen has a slight negative charge
– Because of this unique polarity in charge,
other substances that are charged, such as
table salt, can dissolve in water.
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Laney College
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Distribution of Water in the Body
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Laney College
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Distribution of Water in the Body
• The adult human body is 56 to 64 percent
water:
• Found inside the cells (intracellular), 60% (muscle
cells)
• Found outside the cells (extracellular), 40%
 Water between cells (interstitial)
 Connective tissue, joints, spinal fluid, mucus
• Men have higher percentages than do
women.
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Laney College
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Is Bottled Water Better?
• Despite lack of
scientific research,
consumers believe
that bottled water is
better for them. It
may be safer for
health. But is it
“safer” for the
environment?
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Laney College
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Bottled Water
• FDA regulates bottled water if it crosses state lines
• 25% bottled water comes from tap water
• Spring water comes from an underground source, must
maintain the composition found at the source, and
must contain less than 250 ppm solids
• Mineral water is the same as spring water except it has
greater than 250 ppm solids and no minerals can be
added
• Sparkling water is similar to spring water but must have
dissolved carbon dioxide present at its source
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Laney College
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Water Balance
• Highest fluctuating nutrient must balance water
depletion with ingestion
• Water has no storage mechanism
• Water loss depends on
– Environmental temperature, age, activity level
• Water is loss in respiration (lungs), urine & feces
• Infants lose more relative to weight
• Remember, the main function of water is to cool
the body
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Laney College
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Laney College
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Hydration: Water Intake and
Retention
• Thirst is controlled by the hypothalamus
• Thirst not best indicator of hydration may lag
behind actual body’s needs
• Antidiuretic hormone secreted by pituitary gland
– Signals kidneys to retain water
• Aldosterone secreted by adrenal glands
– Signals kidneys to retain sodium resulting in holding
onto water
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Laney College
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How Much Water Should
We Drink?
• 1.5 mL/kcal or 8–12 cups per day (including
beverages and water in food)
• May need more if:
– Pregnant
– Breast feeding
– Exercising
• ¾–1.5 cups for every 15 minutes
– On a high-protein diet to remove amines & ketone
bodies
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Laney College
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Staying Hydrated During Exercise
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Drink before, during, and after exercise
Drink early, drink often
Before: 1.5–2.5 cups of fluid every 2–3 hours
During: ¾ to 1.5 cups every 15–20 min
After: 2–3 cups first 30 minutes after exercise;
4 – 4.5 cups every 1–2 hours until body weight
is back to pre-exercise level
• Do not drink just plain water need to replace
electrolytes, especially sodium
• Select foods high in water
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Laney College
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Dangers of Dehydration
• Decrease in extracellular water concentration
will result in water be taken from the cell
(intracellular water) causing dehydration
• 1 - 2% can cause lack of concentration, mild
fatigue, and impaired athletic performance
• 5% can lead to cramping and heat exhaustion
• 7 – 10% causes hallucinations and heat stroke
• Occurs with diarrhea & vomiting
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Laney College
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Laney College
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Dehydration in Infancy
• Increased ratio of surface area to body volume =
greater water loss
– Greater requirement relative to weight
– Greater metabolic rate
• Diarrhea and vomiting increase chances of
dehydration
• Infants need 2 oz. of fluid/day per pound of weight
– Easily met by breast milk or formula
• Oral rehydration solution – Pedialyte
• With hotter weather need to increase fluids
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Laney College
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Signs of Dehydration in Infants
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Dry mouth and tongue
No tears even when crying
Irritability
No wet diapers for three hours or more
(five to six wet diapers are normal)
• Sunken eyes and cheeks
• Inactivity or sleepiness
• Sunken soft spot on the head
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Laney College
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Role of Kidneys & Urine in Water Balance
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Laney College
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Role of Kidneys in Water Balance
• Nephrons in your kidneys control the
composition of urine and blood; they filter the
blood
• Hormonal signals tightly control what is filtered
and what is excreted as urine
• Water and electrolytes are reabsorbed based
on your body’s needs and hydration level
• At rest 1 liter of blood is filter per minute
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Laney College
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Role of Urine in Water Balance
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Major source of water loss
You produce 4–8 cups of urine per day
Water, electrolytes, urea, creatinine
Urea is a waste product of protein and muscle
metabolism
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Laney College
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Electrolytes: Sodium (Na⁺),
Potassium (K⁺) & Chloride (Cl¯)
• Electrolytes = minerals that when placed in water
become charged particles
• Cations - Positively charged (sodium extracellular
and potassium intracellular)
• Anions - Negatively charged (chloride) associated
with sodium (extracellular)
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Laney College
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Should someone who does not exercise
be concerned about electrolytes?
• It depends on which electrolyte.
• Sodium: No
– DRI for sodium = 1,500 mg
– Table salt is 40 percent sodium.
– The average American consumes eight to twelve times the
estimated daily requirement.
• Potassium: Yes
– DRI 5,700 mg; many people do not get this amount.
– One banana = 450 mg
• Chloride: No
– 2,300 mg/day consumed with sodium
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Laney College
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Dietary Sodium
• DRI – 1500 mg/day
• Most sodium consumed
is from processed
foods, not table salt
• 50 - 75% of sodium in
the American diet is
added to food by
manufacturers
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Laney College
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Laney College
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Chloride in Food
• Natural Cl¯ content in most food is low
• 1 g sodium chloride or table salt is 600 mg
chloride (60%)
• Most Americans consume 10 to 15 g of salt
during cooking or adding at table
• Easy to exceed the DRI of 2,300 mg
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Laney College
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Laney College
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Potassium
• DRI - 5700 mg/day
• Not usually added to foods
• Good sources are fresh fruits and vegetables
– Tomatoes, carrots, potatoes, beans,
peaches, pears, squash, oranges, bananas
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Laney College
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Sodium and Hypertension
• A diet high in sodium may increase risk for
high blood pressure
• 25% of Americans have high blood pressure
known risk factor for coronary heart disease &
stroke
• Essential hypertension – high blood pressure
with no known cause (most cases)
• Most treatable
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Laney College
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High Blood Pressure
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High blood pressure 140/90
Systolic, top number
Diastolic, bottom number
To treat
– Lose weight
– Reduce sodium in some
people
– Consume adequate
potassium
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Laney College
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Laney College
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High Blood Pressure
• Salt sensitive – some people will have an
increase in blood pressure on a high Na⁺ diet
• Low Na⁺ diets are often recommended for
people with high blood pressure
• Potassium seems to provide an
antihypertensive effect by relaxing blood
vessels
– maintain a balance between K⁺ and Na⁺
• A lack of magnesium and calcium may also
contribute to high blood pressure
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Laney College
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Absorption and Function of
Electrolytes
• Sodium is absorbed by several mechanisms in
the small intestine and colon along with
chloride.
– Helps absorption of amino acids, glucose,
and some B vitamins
• Potassium absorption occurs along the length
of the intestines, especially the colon.
– Necessary for the movement of sodium
across the small intestine & colon
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Laney College
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Physiological Functions
• The movement of water and electrolytes
across cells is important for the maintenance
of health and normal functions
• Water and electrolytes move across cells by
two processes
– Osmosis
– Diffusion
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Laney College
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Physiological Functions
• Osmosis is the movement
of water across a
membrane from an area
where there are fewer
particles to an area where
there are more particles
in order to equalize the
concentration in both
cells
– Membrane is permeable
to the water but not to
the salt in this example
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Laney College
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Physiological Functions
• Diffusion is the movement of electrolytes from
an area of greater concentration to an area of
lesser concentration
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Sodium and Potassium and Nerve Transmission
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Physiological Functions
• Chloride is part of stomach acid (HCl)
• Electrolytes buffer body fluids
• Electrolytes enhance water absorption
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Deficiencies
• Sodium deficiency is rare.
– Hyponatremia – occurs with dehydration or if
water is replaced with no sodium
• Potassium deficiency – hypokalemia
– Use of laxatives and diuretics
– Excessive vomiting and/or diarrhea
– Kidney disease
– Extreme weight loss
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Sports Drinks
• Enhance water absorption and replace lost
electrolytes
• Not needed in events less than one hour
• 6% glucose ideal
• 2.5 cups per pound of weight lost
• Help replace sodium and potassium
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Laney College
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