2. Water and Electrolyte Balance Flashcards
What are the body water contents of newborns, adult males, and adult females?
Newborn - 80%
Adult male - 60%
Adult female - 50%
What are the sources of water intake?
Metabolism 10%, food 30%, beverages 60%
What are the output sources of water?
Faeces 4%, sweat 8%, loss via skin and lungs 28%, urine 60%
What are the two main body fluid compartment?
Intracellular and extracellular fluid.
What are the sections of extracellular fluid?
Interstitial fluid, plasma, lymph, transcellular fluid.
How do things move between body fluid compartments?
Osmotic and oncotic pressures, hydrostatic pressure, diffusion, facilitated diffusion, active transport, vesicular transport.
What is the normal osmolality of plasma?
= interstitial fluid = intracellular fluid = 280-310mOsm/kg.
Which ions mostly determine osmolality?
Na+ and Cl- in ECF; K+ in ICF.
What is the cell membrane permeable to out of the following: Na+, K+, urea, water?
Yes - water, urea.
No - Na+, K+.
What is the capillary wall permeable to out of the following: water, urea, Na+, K+, plasma protein?
Yes - water, urea, Na+, K+.
No - plasma protein.
How does ingesting lots of NaCl impact cell size?
Concentration rises in ECF so water shifts out into ECF until osmolarity balances => cell shrinks.
How does drinking large volumes of water impact cell size?
Water moves into cells (ECF -> ICF) => cells swell, brain oedema, brain death.
If 1L of water (as 5% dextrose osmotically correct) is infused, which body fluid compartment(s) will it be in and why?
Everywhere - cells take up glucose quickly so water moves from plasma to all compartments (including ICF).
If 1L of 0.9% NaCl saline is infused, which body fluid compartment(s) will it be in and why?
Stays in the ECF as there’s no reason for it to move into the cells.
What regulatory mechanisms are relevant in body fluid control?
Thirst, ADH, RAAS.
