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Transcript
Chapter 8
Water and
Electrolytes:
Striking a Balance
Laura Coronado
Laney College
1
A Water Molecule
• Inorganic (no carbon)
Laura Coronado
Laney College
2
Water’s Charge Distribution
Laura Coronado
Laney College
3
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.
Laura Coronado
Laney College
4
Distribution of Water in the Body
Laura Coronado
Laney College
5
Laura Coronado
Laney College
6
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.
Laura Coronado
Laney College
7
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?
Laura Coronado
Laney College
8
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
Laura Coronado
Laney College
9
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
Laura Coronado
Laney College
10
Laura Coronado
Laney College
11
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
Laura Coronado
Laney College
12
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
Laura Coronado
Laney College
13
Staying Hydrated During Exercise
•
•
•
•
•
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
Laura Coronado
Laney College
14
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
Laura Coronado
Laney College
15
Laura Coronado
Laney College
16
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
Laura Coronado
Laney College
17
Signs of Dehydration in Infants
•
•
•
•
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
Laura Coronado
Laney College
18
Role of Kidneys & Urine in Water Balance
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Laney College
19
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
Laura Coronado
Laney College
20
Role of Urine in Water Balance
•
•
•
•
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
Laura Coronado
Laney College
21
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)
Laura Coronado
Laney College
22
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
Laura Coronado
Laney College
23
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
Laura Coronado
Laney College
24
Laura Coronado
Laney College
25
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
Laura Coronado
Laney College
26
Laura Coronado
Laney College
27
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
Laura Coronado
Laney College
28
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
Laura Coronado
Laney College
29
High Blood Pressure
•
•
•
•
High blood pressure 140/90
Systolic, top number
Diastolic, bottom number
To treat
– Lose weight
– Reduce sodium in some
people
– Consume adequate
potassium
Laura Coronado
Laney College
30
Laura Coronado
Laney College
31
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
Laura Coronado
Laney College
32
Laura Coronado
Laney College
33
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
Laura Coronado
Laney College
34
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
Laura Coronado
Laney College
35
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
Laura Coronado
Laney College
36
Physiological Functions
• Diffusion is the movement of electrolytes from
an area of greater concentration to an area of
lesser concentration
Laura Coronado
Laney College
37
Sodium and Potassium and Nerve Transmission
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Laney College
38
Physiological Functions
• Chloride is part of stomach acid (HCl)
• Electrolytes buffer body fluids
• Electrolytes enhance water absorption
Laura Coronado
Laney College
39
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
Laura Coronado
Laney College
40
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
Laura Coronado
Laney College
41