Review of Renal Phys Flashcards
what is the 60, 40, 20% rule?
total body fluid is 60% of the body weight. Intracellular fluid is 40% of the body weight. Extracellular fluid is 20% of the body weight
what happens to total body fluid as you age?
decreases with age from 75% of BW at birth to 50% of BW in old age. ECF decreases from 50% of TBF at birth to 30% of TBF in old age.
blood pressure equation
BP = TPR x CO
total peripheral resistance times cardiac output
urine output in dehydration and overhydration
dehydration is less than 1.4 liters per day, overhydration is more than 14 liters per day
what is the function of the kidney
to maintain constant ECF volume and solute composition by acting upon the enormous volume of glomerular filtrate to form urine
how does kidney maintain constant ECF volume?
volume receptors sense changes in pressure and regulate ECF expansion and contraction.
what happens when you change the amount of sodium intake
you throw off the sodium balance and it takes the body a few days to readjust
what happens when you decrease dietary sodium intake
induces decreased urinary sodium output by adjusting the magnitude of sodium reabsorption until sodium balance is achieved.
edema
excess accumulation of fluid in the interstitial space due to cardiac, renal, hepatic, or endocrine dysfunction.
what causes edema
imbalance of hydrostatic and oncotic pressures across the capillary wall induces a shift in fluid distribution from the intravascular to the extravascular space, resulting in isotonic retention of sodium and water and decreased circulating volume
what does decreased renal perfusion pressure cause?
activation of the renin-angiotensin-aldosterone system, which further increases sodium retention and edema
how do diuretics work
forcing increased elimination of sodium and water in urine. this decreases hydrostatic pressure and inreases oncotic pressure, favoring absorption of edematous fluid
renal clearance
defined as volume of plasma cleared of a solute per unit time. measured in ml/min.
how do you estimate measurement of GFR?
use renal clearance of inulin or creatinine. these do not go through reabsorption or secretion, and therefore the amount excreted is equal to the amount filtered.
what percentages are negative or positive water balances?
when the fractional excretion of water is less than 1%, negative water balance. more than 1% is a positive water balance
what do alkalosis and acidosis induce?
alkalosis induces potassium secretion, acidosis decreases potassium secretion
thick ascending loop of henle
impermeable to water. mediates solute reabsorption in absence of water reabsorption, diluting the tubular fluid. counter current multiplication of solute gradient extends from cortex to papilla. this is where the kidney makes dilute or concentrated urine
how is normal ECF volume preserved
achieved by the ability of the kidney to maximize or minimize the osmolarity of the urine in response to ECF volume contraction and expansion
ADH and its relationship to ECF and osmolarity
ADH increases when osmolarity increases. ADH increases water permeability of collecting duct, which allows reabsorption of water (negative free water clearance). vice versa for low plasma osmolarity.
late distal tubule and collecting duct
sodium reabsorption in the late distal tubule and collecting duct is regulated by circulating levels of aldosterone which varies according to the prevailing sodium balance. sodium reabsorption is coupled to potassium secretion. potassium secretion is regulated by aldosterone.
what are diuretics?
drugs which increase the volume and rate of urine output by decreasing active reabsorption of sulutes and/or water in one or more segments of the nephron. they change the volume and ion concentration of the ECF by changing the volume and ion concentration of the urine.
therapeutic uses of diuretics
hypertension, edema, calcemia and kalemia
effect of the different types of diuretics on concentration and dilution of the urine
loop diuretics decrease capacity of kidney to concentrate and dilute urine in response to decreased and increased water consumption. decrease solute reabsorption in cortical talH and medullary talH. thiazide diuretics decrease the capacity of the kidney to dilute the urine in response to increased water consumption. they decrease solute reabsorption in the early distal tubule.
reabsorption of carbonic acid
carbonic anhydrase turns H2CO3 into CO2 and H20, which goes into the cell. here, a different carbonic anhydrase turns it back into H2CO3, which turns into H and HCO3. the H+ is used to make H2CO3 outside of the cell. the HCO3 is reabsorbed.
