11-fluids & electrolytes

8/10/2019 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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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Minerals: Phosphorus (P)6. DRI-RDA

l adults: 700mg/day

l DRIUL

l adults: 4000mg/day

11-fluids & electrolytes

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