chapter 8 water and electrolytes: striking a balance

Laura Coronado Laney College 1

Chapter 8

Water and Electrolytes:

Striking a Balance

A Water Molecule

• Inorganic (no carbon)


Water’s Charge Distribution


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.


Distribution of Water in the Body


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.


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?


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


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


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


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


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 waterLaura 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


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


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


Role of Kidneys & Urine in Water Balance


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


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


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)


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


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


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


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


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


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


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


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


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


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



• Diffusion is the movement of electrolytes from an area of greater concentration to an area of lesser concentration


Sodium and Potassium and Nerve Transmission



• Chloride is part of stomach acid (HCl)• Electrolytes buffer body fluids• Electrolytes enhance water absorption


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


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


chapter 8 water and electrolytes: striking a balance

Documents