flow and filtration Flashcards
renal clearance: define renal clearance, explain the use of renal clearance in assessing renal function, and be able to perform the appropriate calculation given appropriate values
what is clearance
extent to which a substance is removed from blood; number of litres of plasma completely cleared of substance per unit time, used to measure glomerular filtration rate
clearance equation
(concentration of substance in urine x rate of urine production)/concentration of substance in plasma; low = retained, high = secreted
to measure glomerular filtration rate from clearance, what must the substance be
freely filtered and neither reabsorbed nor secreted, so amount filtered = amount excreted
what molecule is used to measure glomerular filtrate rate (by measuring clearance) by transfusing it into the body
inulin (plant polysaccharide, freely filtered and not reabsorbed or secreted, not toxic, measurable in urine and plasma)
what molecule is used to measure glomerular filtrate rate (by measuring clearance) produced in the body
creatinine
features of creatinine that make is suitable to use to measure clearance and glomerular filtration rate
waste product from creatine in muscle metabolism; amount of creatinine released is fairly constant; if renal function stable, amount of creatinine in urine is stable; low values of creatinine clearance may indicate renal failure; high plasma creatinine may indicate renal failure (not excreted so decrease gradient so builds up in plasma)
significance of molecules with rates below 120ml/min
more actively reabsorbed into plasma
what is renal plasma flow measured by
PAH clearance (625ml/min)
why can PAH clearance be used to measure renal plasma flow
filtered and more actively secreted in one pass of kidney (completely excreted)
what happens to excretory products if glomerular filtrate rate falls
build up in plasma
what is diagnostic of renal disease
raised plasma concentration of creatinine
what is pharmacokinetics
drug doses taking into account renail failure, causing overdose as builds up in plasma
integrated functions of the kidney
excretion of metabolic products (urea, uric acid, creatinine); excretion of foreign substances (drugs - pharmacokinetics); homeostasis of: body fluids and electrolytes (affecting cell volume), and acid-base balance; regulate blood pressure - cardiovascular; secrete hormones - endocrinology
what 2 hormones are secreted by the kidney
renin, erythropoietin
