FNH 250 M.10 - Water and the Electrolytes

What % of an adult’s body is water?

about 60%

What are key functions of water?

solvent, transports nutrients/waste, temperature regulation, joint lubrication, blood volume/pressure control, chemical recactions

what are the two main fluid compartments in the body?

intracellular (inside cells) and extracellular (outside cells)

what are the two parts of extracellular fluid?

interstitial (between cells) and intravascular (in blood vessels)

what is water balance?

when water intake equals water output

what are the 3 sources of water intake?

beverages, food, metabolic water

what are the 4 sources of water loss?

urine, feces, lungs, skin

what is obligatory water loss?

minimum 500 mL/day needed to remove waste

what is dehydration?

when water output exceeds input; causes weakness, confusion, death

what is water intoxication?

too much water —> low sodium (hyponatremia); symptoms; confusion, seizures

what controls thirst?

The hypothalamus

Why should you drink before you are thirsty?

Thirst lags behind actual hydration needs

What is the AI for total water intake?

Men: 3.7 L/day

Women: 2.7 L/day

(includes food + drinks)

what is an electrolyte

An ion from dissolved salts (e.g., Na⁺, K⁺, Cl⁻, PO₄³⁻)

where are Na+ and Cl- found mostly?

extracellular fluid

What regulates electrolyte movement?

Protein channels and pumps

What happens if electrolytes are imbalanced in cells?

too high —> cell swells/bursts; too low —> cell shrinks/collapses

what controls electrolyte balance in the body?

GI tract (absorption) and kidneys (excretion)

What are sodium’s key roles?

fluid balance, nerve signals, muscle contraction

what is hyponatremia and what causes it?

low blood sodium from water overload or heavy losses (eg. sweat, diarrhea)

what is the AI and CDRR for sodium?

AI = 1500 mg/day; CDRR = 2300 mg/day

what are major sodium sources in the diet?

75% from processed foods (eg. soup, sauces, snacks)

what is the best way to reduce sodium intake?

reduce processed foods, use herbs instead of salt

How does sodium affect blood pressure?

High sodium increases BP

What is the DASH diet?

diet high in fruits, veg, legumes; reduces sodium and saturated fat; lowers BP

what are chloride’s functions?

fluid balance, part of stomach acid (HCl)

what is chloride’s main dietary source?

Table salt (NaCl)

what are potassium’s functions?

fluid balance, nerve/muscle function, lowers BP

what is potassium’s relationship with sodium?

it has opposite effects — higher potassium lowers BP

what are potassium deficiency symptoms?

muscle weakness, irregular heartbeat, high BP

what is the AI for potassium?

Men: 3400 mg/day

Women: 2600 mg/day

what are good sources of potassium?

fresh fruits and vegetables (banana = 400 mg, baked potato = 1000 mg)

where is most phosphorus found in the body?

in bones (as part of hydroxylapatite)

what are phosphorus’s functions?

bone health, fluid buffer (pH), DNA/RNA/ATP synthesis, phosphorylation of enzymes

what are symptoms of phosphorus deficiency?

muscle weakness, bone pain (rare)

what are good sources of phosphorus?

milk, meat, poultry, legumes, seeds

what is the RDA for phosphorus?

700 mg/day