bodily fluid control (midterm 3) Flashcards
what do the kidneys do
maintain bodily fluid volumes and compositions
how much water does a 70 kg person contain
42 liters of water (60%) (Vt)
how many liters of water are inside the 75 trillion cells of the body and what are they part of
28 liters - intracellular fluid (Vic)
how many liters of water are extracellular
14 - 11 are interstitial (Vis), 3 are plasma (Vp)
how many liters of water are blood and how many are plasma
5 liters; 3 liters
how do you measure total body water
add a bolus of radioactive water and measure concentration after a few hours (Vt)
how do you measure extracellular fluid volume
add a bolus of radioactive sodium and measure concentration after a few hours (Vec)
how do you measure intracellular fluid volume
equals total body water minus extracellular fluid volume (Vic)
how do you measure plasma volume
add a bolus of radioactive serum albumin and measure concentration after a few hours (Vp)
how do you measure interstitial fluid volume
equals extracellular fluid volume minus plasma volume (Vis)
how do you measure total blood volume
plasma volume / (1 minus hematocrit)
hematocrit = total blood cell volume
what is osmosis
the diffusion of water, through a selectively permeable membrane, from a region of low solute concentration to high solute concentration
why does osmosis happen
water moves to try to equilibrate solute concentration on either side of the membrane
what is an osmole
the total number of particles in solution that are establishing an osmotic gradient
= moles x dissociable particles
what is the normal value for osmoles
280 mOsm/L
dominated by Na+, glucose, urea
what is osmosis equilibrium
if a cell is placed in a solution with normal osmolarity (280 mOsm/L) the cell will neither shrink or swell - isotonic solution
what is a hypotonic solution vs hypertonic solution
solution with less osmolarity vs solution with more osmolarity
what does a hypotonic solution result in
the cell will swell as it tries to dilute its solutes
what does a hypertonic solution result in
the cell will shrink as it tries to concentrate its solutes
what two basic principles guide the discussion of fluid regulation
- intracellular = extracellular osmolarity due to water transport across membrane
- total osmolarity of a system (intracellular + extracellular) is constant unless added or removed
if a hypertonic solution is administered to a patient, what happens?
- The osmolarity of the extracellular fluid increases, intracellular decreases
- Osmosis pushes water out of the cell and into the extracellular space
if a hypotonic solution is administered to a patient, what happens?
- The osmolarity of the extracellular fluid decreases, intracellular increases
- Osmosis pushed water into the cell and out of the extracellular space
what is an edema
the presence of excess fluid in the body, typically in the extracellular fluid space but sometimes involving the intracellular fluid space
what two conditions lead to an intracellular edema and how common are they
RARE
- Depression of metabolic systems of the tissues
- Inadequate nutrient delivery to the cell
what two conditions lead to an extracellular edema and how common are they
COMMON
- Abnormal leakage of fluid from the plasma through the capillary wall and into the interstitial space
- failed lymphatic drainage
what is the equation that describes capillary filtration and what does each variable stand for
Filtration = Kf x (Pc - Pif - πc + πif)
- Kf = capillary filtration coefficient
- Pc = capillary hydrostatic pressure
- Pif = interstitial fluid hydrostatic pressure
- πc = capillary osmotic pressure
- πif = interstitial osmotic pressure
what increases capillary filtration
increased Kf, increased Pc, decreased πc
what results in heart failure
decreased cardiac output, increased capillary pressure leads to increased capillary filtration
what results in renal failure
decreased Na+/H2O excretion, increased blood volume, increased arterial pressure, increased Pc leads to increased capillary filtration
what three safety factors prevent an edema
- increased interstitial fluid volume will lead to increased interstitial fluid pressure
- the ability of the lymph flow to increase 10-50 fold
- washdown of interstitial fluid protein
