11-Fluids & Electrolytes
Transcript of 11-Fluids & Electrolytes
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Fluids & Electrolytes
Nutrition Concepts and
Controversies (FNH 250)
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I. Introduction: Waterl water is essential to life
l need more water each
day than any other
nutrientl ~50-70% of body weight;
%body fat %water
l is the body's transport,
reactive, and solvent
medium
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I. Introduction: Waterl there are different compartments of fluid in the
body
l INTRACELLULAR = inside cells (~25 Ltr)
l EXTRACELLULAR = outside cells
l INTERSTITIAL = between cells (~14 Ltr)
l INTRAVASCULAR = within bloodstream (~3
Ltr)
l DIGESTIVE JUICES
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I. Introduction: Waterl interstitial fluid is important for supplying nutrients
from the bloodstream to the cells and for removingwaste products from the cells to the bloodstream
l if too much water enters cells, they rupture
l if cells lose too much water, they collapse
l water flows freely through cell membranes, followingminerals (ions)
l ions and other nutrients easily dissolve in water
allowing the body to move fluids between body fluid
compartments
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I. Introduction: Mineralsl minerals represent about 4% of our body weight
l some minerals act as CO-FACTORS = a mineralelement that, like a coenzyme, works with anenzyme to facilitate a chemical reaction
l when a mineral salt (e.g. NaCl) dissolves in water, itseparates into 2 ions (Na+ & Cl-); each ion issurrounded by water molecules
l an ion is a charged particle (ex. Calcium-Ca2+, Iron-Fe2+, Chloride-Cl-, Fluoride-F-)
l positively charged ions are called
l negatively charged ions are called
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I. Introduction: Mineralsl some minerals are readily absorbed, transported
freely and are excreted by the kidneys (e.g.,
Potassium-K); other minerals need special carriers
to be absorbed and transported (e.g., Calcium-Ca)l minerals taken in excess can be toxic
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I. Introduction: Mineralsl minerals have variable BIOAVAILABILITY the
ease at which a nutrient is absorbed
l "binders" in food such asphytic acidin whole
grains and legumes and oxalic acidin vegetables
and fibres may combine with minerals (e.g.
Calcium and Iron) to inhibit their absorption
l digestive tract conditions
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I. Introduction: Mineralsl some minerals interact and compete with each other
for absorption, therefore, consuming an excess of
one mineral may affect the absorption, metabolism,
and/or excretion of anotherl calcium and iron argument against single
nutrient supplements
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I. Introduction: Mineralsl minerals are involved in many varied and important
metabolic roles, including:
l electrolytes that help maintain fluid balance
l essential components of certain compounds
l proper bone growth, development and structural
integrity (e.g., Ca, P, Mg)
l nerve transmission and muscle contraction
l release of energy from the macronutrients
l minerals found free in nature in water (rivers,
streams, oceans), topsoil, and beneath the earth'ssurface
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I. Introduction: The Balancing Act of
Water &Ions in the Bodya. Cell Membranes
l most cations are under controlled flow across
membranes by the action of protein 'pumps' in the
membranes (e.g. Sodium/Potassium ATPase);
anions follow cations
l however, water flows freely between body
compartments, following the ions to the more
concentrated solution
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I. Introduction: The Balancing Act of
Water &Ions in the Bodya. Cell Membranes
l ions in water conduct electricity, thus are calledELECTROLYTES
l all body fluids that contain water and ions are
examples of electrolyte solutions
l important electrolytes for maintaining fluid balancein the body are Sodium (Na+), Potassium (K+),
Chloride (Cl-) and Phosphorus (PO43-)
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I. Introduction: The Balancing Act of
Water &Ions in the Bodyb. Osmosis
l the amount of water in each fluid compartment is
controlled by the ion concentration in each
compartment and the selective movement of ions
across cell membranes
l water flows easily across cell membranes; ions dont
l concentrations of cations and anions in the various
body fluid compartments are normally held within a
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I. Introduction: The Balancing Act of
Water &Ions in the Bodyb. Osmosis
l when cells pump electrolytes in or out, water followsby flowing to the more concentrated solution, alteringthe fluid volume on either side of the semi-permeable
cell membrane, until there is electrical neutrality and asimilar concentration exists on each side of the cell
membrane
l the process of moving water across a membranetoward the more concentrated solution is called
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I. Introduction: The Balancing Act of
Water &Ions in the Bodyb. Osmosis
l water volume inside cells depends primarily on
intracellular Potassium (K+) and Phosphate (HPO42-)
concentrationsl water volume outside cells depends primarily on
extracellular Sodium (Na+) and Chloride (Cl-)
concentrations
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II. Water1. FUNCTIONS OF WATER
l Necessity of Water
l water is vital to life
l different tissues contain varying amounts of water
a. Transport function takes nutrients to cells
b. Reactive function for example, involved in
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II. Water1. FUNCTIONS OF WATER
l Necessity of Water
c. Solvent function
l the major waste product from the body is UREA
l a healthy urine volume: 1-2 Litres/day
l control of urine production determined by thefollowing nutrients:
l protein intake -urea
l sodium intake -saltl fluid intake
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II. Water1. FUNCTIONS OF WATER
Maintenance of Blood Volume and Blood Pressurel kidneys constantly adjusting blood volume and
concentration of the urine
l extreme losses of water from the body (skin,lungs, feces, urine) lead to a decrease in bloodvolume and blood pressure
l hormones, enzymes and blood proteins are allinvolved in maintaining blood volume & pressure
l Antidiuretic Hormone
secreted from pituitary gland in response to
high salt concentration in the blood
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II. Water1. FUNCTIONS OF WATER
hormones, l Aldosterone hormone that causes kidneys to
retain Sodium in the blood and water follows
sodium, increasing blood volume
when blood volume increases, blood pressure
increases, when blood volume decreases,
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II. Water
1. FUNCTIONS OF WATER
Temperature Regulationl our body has a high water content which benefits
us by allowing us to warm up or cool down slowly
l the body loses fluids via perspiration, evaporation
must occur to cool the body temperature
l 1 litre of perspiration = ~600 kcal energy
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II. Water1. FUNCTIONS OF WATER
l Acid/Base Balance (pH)
l careful acid/base balance is maintained in thebody with the goal of controlling the blood pH
level within a narrow range of 7.35-7.45, mostlyachieved by the action of the kidneys, buffers inthe blood, and respiration
l when blood pH shifts outside this range, candamage proteins (e.g. Hb, enzymes)
l some electrolytes act to accept or donate
hydrogens to maintain a normal and constantbody pH = buffers
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II. Water2. WATER NEEDS
l Continued Thirst
l body begins to conserve water
l the brain releases AntiDiuretic Hormone (ADH)which forces kidneys to reabsorb water rather
than excrete it
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II. Water2. WATER NEEDS
l Can You Drink Too Much Water?
l when kidneys' ability to excrete water is
exceeded, results in a condition ofHYPONATREMIA, low circulating levels of
Sodium
l extreme cases of water toxicity can lead to death
(e.g., marathon runners)
l symptoms: headache, blurred vision, diarrhea,exhaustion, mental confusion, fainting
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III. Fluid & Electrolyte Balance Major
Minerals: Sodium (Na)1. FUNCTIONS OF SODIUM
l Blood Acid/Base Balance
l kidneys filter all Na+ out of the blood and returnonly the amount of Sodium the body needs
(analogy: cleaning the car)
l instead of the kidneys excreting Na+ ions, thekidneys can swap H+ ions for Na+ ions, keeping
the Na+ ions in the body and excreting H+ ions inthe urine, thus reducing the acid load in the body
l Nutrient Absorptionl active transport of some nutrients (e.g., GLU) into
the intestinal cells requires
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III. Fluid & Electrolyte Balance Major
Minerals: Sodium (Na)2. SODIUM DEFICIENCY
l HYPONATREMIA, unlikely due to high intakes ofSodium in North American diets, but may occur withprolonged vomiting, diarrhea and/or heavy sweating
l symptoms: muscle cramps, dizziness, mentalapathy, can lead to shock and coma
l athletes participating in endurance events should
consume sports drinks/gels containing sodium salts
l at 3-5% of total body weight loss as perspiration
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III. Fluid & Electrolyte Balance Major
Minerals: Sodium (Na)3. SODIUM TOXICITY
l HYPERNATREMIA, not usually a problem exceptwith salt-sensitive people in whom it is likely to leadto hypertension, or if you have renal (kidney)
problemsl if you have a high sodium intake, you should ensure
you drink enough water
l note: water intake will not decrease your sodiumintake, but will help reduce risk of hypernatremia
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III. Fluid & Electrolyte Balance Major
Minerals: Sodium (Na)5. SODIUM IN FOODS
l Sources
l ~75% obtained from processed foods
l ~15% added during cooking or at table as table
salt
l ~10% from unprocessed foods -
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III. Fluid & Electrolyte Balance Major
Minerals: Sodium (Na)6.DRIAI
l Adults
l (19-50 yrs) 1500mg/d
l (51-70 yrs) 1300mg/d
l (70+ yrs) 1200mg/d
l DRI-UL all adults: 2300 mg/day
l ~100 mg/d minimum needed by body
l AIl based on obtaining a nutritionally adequate diet
for other nutrients and for replacing losses of sodiumin sweat in moderately active people
l average intake ~3000 mg/d (3 g) = 7.5 g salt/day
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III. Fluid & Electrolyte Balance Major
Minerals: Potassium (K)1. FUNCTIONS OF POTASSIUM
l Intracellular Fluid (ICF)
l major cation inside cells (95%), therefore, mainelectrolyte regulator of ICF volume
l Nerve Conduction/Muscle Contraction
l Potassium contributes to nerve impulse
transmission and muscle contraction by tradingplaces with Sodium before being pumped back to
the appropriate fluid compartments
l a proper K+ concentration is required for a
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III. Fluid & Electrolyte Balance Major
Minerals: Potassium (K)2. POTASSIUM DEFICIENCY
l HYPOKALEMIA unlikely, although we absorb ~90%of Potassium intake, we should still meet the dailyDRI
l most likely occurs due to excessive losses (ratherthan low intakes), with the exception of alcoholicswith poor dietary habits
l caused by prolonged vomiting, dehydration,diarrhea, regular use of diuretics, steroids, strong
laxatives and some drugs
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III. Fluid & Electrolyte Balance Major
Minerals: Potassium (K)2. POTASSIUM DEFICIENCY
l low (and high) blood Potassium levels are lifethreatening affecting the heart beat
l symptoms:
l loss of appetite, muscle weakness and cramping,confusion
l irregular heart beat decreased ability to pumpblood and nourish the body cells
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III. Fluid & Electrolyte Balance Major
Minerals: Phosphorus (P)2. FUNCTIONS OF PHOSPHORUS
l Fluid Balance
l major intracellular anionic electrolyte that workswith Potassium to regulate fluid volume inside
cellsl Bone
l ~85% of all body Phosphorus is found withCalcium in the hydroxyapatite crystal found in
bones and teeth
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III. Fluid & Electrolyte Balance Major
Minerals: Phosphorus (P)6. DRI-RDA
l adults: 700mg/day
l DRIUL
l adults: 4000mg/day