Fluid and Electrolyte Balance Unit 3 a&p

what is fluid composition

what is difference in female

45% solids, 55% fluids

2/3 intracellular fluid, 1/3 extracellular fluid (80% interstitial fluid, 20% plasma)

more adipose tissue than male, carries more water

What are solutes

How are they classified

substances dissolved in water

nonelectrolytes and electrolytes

Nonelectrolytes

most are organic molecules

do not dissociate in water

ex. glucose, lipids, urea, creatinine

no charged particles created

Electrolytes

Dissociate into ions in water

ex. inorganic salts, all acid and bases, some proteins

ions conduct electrical current

greater osmotic power than nonelectrolytes (dissociate into 2 or more ions, fluid shift)

Electrolytes distribution

Na+ more in extracellular fluid

K+ more in intracellular fluid

HPO4- is primary anion inside cells

What regulates continuous exchange and mixing of fluids

osmotic and hydrostatic pressures

water moves freely among osmotic gradients

all body fluids osmolarity is almost always equal

what is proportional to change in solute concentration

net water flow

increase ECF osmolality (more dissolved solids)= water leaves cell

decrease ECF osmolality (less dissolved solids) = water enters cells

Where do the exchanges occur

Exchanges between plasma and interstitial fluid occur across capillary walls

fluid leaks from arteriolar end of capillary, reabsorbed at venule end

lymphatic pick up remaining fluid and send to blood

Exchange between intersitial fluid and intracellular fluid occurs across cell membranes

Water Balance

what is water intake

what is water output

water intake must equal water output: 2.5 L a day

intake: most water is taken in via ingested foods and beverages, small amount from metabolism

output: urine (60%), insensible water loss (skin/lungs), perspiration, and feces

Obligatory water losses

insensible vs sensible loss

explains why we cannot live without water for very long

insensible water loss from lungs or skin

sensible water loss from urine to excrete waste (60%), obvious sweat (8%), feces (4%)

Regulation of Water Intake

thirst mechanism is driving force for water imbalance

Governed by hypothalamus thirst center

hypothalamus osmoreceptors detect ECF osmolality and is activated

how are hypothalamic osmoreceptors activated

increase plasma osmolality of 1-2%

dry mouth

decrease blood volume/pressure

angiotensin 2

how is the thirst center inhibited

drinking water inhibits thirst center

inhibitory feedback signals: relief of dry mouth, activation of stomach stretch receptors

Influence of ADH

water reabsorption in collecting ducts = ADH release

decrease ADH = dilute urine, decrease volume of body fluids

increase ADH = concentrated urine bc of reabsorption of H2O, increase volume of body fluids

other factor that trigger ADH release

large changes in blood volume/pressure

increase ADH, diarrhea, vomitting

dehydration and hypotonic hydration

dehydration: if more water than solutes is lost, cells shrink, decrease ECF pressure

hypotonic hydration: more water than solutes gained, cells swell, increase ECF pressure

Electrolyte balance

usually refers only to salt balance, even through electrolytes includes acids, bases, proteins

salts control fluid movement and membrane permeability

salts enter body by ingestion and metabolism

salts lost by persperation, feces, urine, vomit