Unit 7 - Introduction to Renal Physiology Flashcards
what are regulatory functions of the kidneys?
- extracellular fluid volume, oxmolarity, and ion composition
- clearance of metabolic end products, toxins, and drugs
- endocrine (erythropoietin, active vit D, renin
how does solute composition VS concentration differ in ICF and ECF?
composition of solute is different (Na more outside, K inside), but concentration/osmolarity is the same (~300 mOsm/L)
how does total body water change with age? with body fat?
decreases (75% in neonates, 50% in aged adults)
- ECF contracts from 50% in neonates to 33% in adults
- TBW is inversely proportional to % body fat, as well as decreases percentage of TBW of body weight (puberty)
what are kidneys the only effector organs of?
regulated water and salt excretion
-compensate for effects of variable consumption of solutes and water on ECF volume and osmolarity by increasing/decreasing excretion of solutes and water in urine
what does unregulated water and salt loss from TBW cause?
sweat, feces, and insensible skin and lung loss (H2O only)
what is fluid distribution between plasma and ISF driven by?
balance between hydrostatic pressure and osmotic pressure differences across capillary wall (opposing Starling forces)
what is the filtration or reabsorption rate formula? their variables?
rate = Lp [(Pc - Pi) - (πc - πi)
- Pc = capillary hydrostatic pressure (filtration)
- Pi = interstitial hydrostatic pressure
- Pc - Pi = push out
- πc = capillary oncotic pressure (reabsorption)
- πi = interstitial oncotic pressure
- πc - πi = pull in
what is oncotic pressure?
osmotic pressure inside and outside the capillary attributable to presence or absence of negatively charged PRO
solute distribution
solute concentration is similar between ISF and plasma, with exception of negatively charged plasma PRO, which are impermeable to capillary wall and remain within intravascular compartment
-osmotic pressure is higher in plasma than ISF due to absence of PRO in ISF
what is Gibbs-Donnan equilibrium?
state of electro-chemical equilibrium with diffusible cation and anion concentration
what is edema?
excess accumulation in interstitial space due to cardiac, renal, hepatic, or endocrine dysfunction
-localized/generalized imbalance of hydrostatic and osmotic pressure across capillary wall, inducing a shift in fluid distribution from intravascular to extravascular space
what can CHF, nephrotic syndrome, and liver disease edema all cause?
isotonic retention of sodium and water, as well as decreased circulating volume
-decreases renal perfusion pressure and activates RAA system, further increasing Na retention maintaining the edema
what is the mechanism of CHF edema VS that of nephrotic syndrome and liver disease?
CHF is increases of capillary hydrostatic pressure (increase filtration), while nephrotic syndrome and liver disease are decreases in plasma PRO concentration, thus capillary oncotic pressure (decrease reabsorption)
what is the only thing that drives net movement of water between ICF and ECF?
osmotic pressure differences across the cell membrane
what is tonicity and what does this determine?
permeating and non-permeating solute concentrations in ICF and ECF; determines water movement
what happens in IV isosmotic fluid gain to ECF?
isosmotic fluid expansion
- increase ECF volume
- no change in ECF osmolarity, osmotic driving force between ICF and ECF, ICF volume or osmolarity
- dilution of plasma PRO
- decreased Hct
what happens in diarrhea (isosmotic fluid loss)?
isosmotic volume contraction
- decreased ECF volume
- no change in ECF osmolarity, ICF volume or osmloraity
- no osmotic driving force between ICF and ECF
- increased PRO concentration and Hct
what happens in profuse sweating and/or water deprivation?
hyperosmotic volume contraction (loss of water in excess of solute from ECF)
- decreased ECF volume
- increased ECF osmolarity
- water moves from ICF to ECF
- -causes decreased ICF volume and increased ICF osmolarity
what happens in high NaCl intake without fluids?
hyperosmotic volume expansion (gain of solute in excess of water)
- increased ECF osmolarity
- ICF NaCl concentration remains unchanged due to Na-K pump activity (Na extrusion) balancing Na entry
- water moves from ICF to ECF
- -causes decreased ICF volume and increased ICF osmolarity
- -increased ECF volume
what happens if syndrome of inappropriate antidiuretic hormone (SIADH)?
hypoosmotic volume expansion (gain of water in excess of solute)
- inappropriate water reabsorption from collecting ducts into ECF causes:
- -increased ECF volume and decreased ECF osmolarity
- -water moves from ECF to ICF
- -increased ICF volume and decreased ICF osmolarity
what happens if adrenal (aldosterone) insufficiency?
hypoosmotic volume contraction; decreased renal NaCl reabsorption causing loss of solute in excess of water
- decreased ECF osmolarity
- water moves from ECF to ICF
- increased ICF volume and decreased ICF osmolarity
- decreased ECF volume
how do cells respond to osmotically driven changes in ICF volume?
activating solute transport mechanisms
-remember that water transport follows solute transport
what is regulatory volume increase (RVI)?
if a cell is shrunk in response to an increase in ECF osmolarity
-cells activate solute uptake mechanisms to increase ICF osmolarity, driving water into cells to restore volume to normal
what is regulatory volume decrease (RVD)?
if a cell has swelled in response to a decrease in ECF osmolarity
-cells activate solute efflux mechanisms to decrease ICF osmolarity, driving water out of cells to restore volume to normal
