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ap fluid & electrolytes

Extracellular fluid (ECF)

makes up the internal environment of the body
1. plasma
2. interstitial fluid = around cells of body
3. lymph
4. transcellular (ex. CFS, synovial fluid)

intracellular fluid

water inside the cells

intracellular fluid functions

solvent that functions to facilitate intracellular chemical reactions that maintain life

Extracellular fluid functions

1. provides a relatively constant environment for cells
2. transporting substances to and from cells


1. Ions in the blood
2. Include: Na+, K+, Cl- (chloride), HCO3-, Ca2+, etc

Na+ Ions

1. Dominant ECF cations
2. Responsible for 90-95% of osmotic pressure

K+ Ions

Dominant ICF cations

Important cations

Na+ = sodium
Ca++ = calcium
K+ = potassium
Mg++ = magnesium

important anions

CI- = chloride
HCO3- = bicarbonate


elevated plasma Na+


decreased Na+


- elevated K+ levels in plasma


- decreased K+ levels

Serum Electrolytes: Sodium (Na)*

Cation - primarily in ECF
Involved in fluid balance
Sodium-potassium pump
Membrane potential

Serum Electrolytes: Potassium (K).*

Cation - primarily in ICF
Membrane potential
Sodium - potassium pump (nervous conduction) is why it's not in ECF
Not involved in fluid balance
Heart very effected

Serum Electrolytes: Calcium (Ca)

Cation - primarily in ECF
Muscle contraction (stored in muscle cell)
Nerve conduction
Skeletal growth
Blood coagulation
Gland secretion

Serum Electrolytes: Magnesium (Mg)

Cation - primarily in ICF
Helps maintain normal muscle and nerve function
Heart rhythm
Immune system
Regulate blood sugar levels
Involved in energy metabolism and protein synthesis
Cofactor in a lot of enzymes

Serum Electrolytes: Bicarbonate (HCO3)

Anion - primarily in ECF
Buffer - acid-base balance

Water enter the body by:

Drink (measure by IV & drink)
Food = fruits & vegtables
Metabolism = H20 made in cellular respiration, catabolism

Water leaves the body by:

Lungs = humidify air, exhaling (regular & rapid) air

Sensible water loss

you can measure (drink, urine)

Insensible water loss

can't measure

Regulation of Water Content

1. Total volume of water in body remains constant
2. Kidneys are primary regulators of water excretion - which are directly controlled by ADH, controls water

what controls water

ADH directly controls water. kidneys regulate

Water content determined by?

osmoreceptors in hypothalamus. Totally based on osmotic pressure in blood.

Increased fluid loss results in?

Triggers thirst and ADH secretion

Decreased fluid loss results in?

Inhibits thirst and ADH secretion

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