Elements of Renal Function Flashcards
kidney function?
regulate ECF concentration
regulate plasma electrolyte concentration
regulate acid base balance
regulate extracellular fluid volume, arterial blood presure
eliminate metabolic waste
hormones in kidney?
erythropoietin
vitamin D
renin
synthesized in kidney?
ammonia
prostaglandins
kinins
glucose
kidney is important?
integrated with many other body systems
renal failure: anemia, osteoporisis, disregulation of calcium and phosphate
kidneys a blood pressure
also regulated
renal blood supply
20% cardiac output
renal BP?
glomerular capillaries - 60 mmHg
-pretty high
pressure in peritubular capillaries
lower (13 mmHg)
permits fluid reabsorption
pressure in capillary beds?
can be regulated by resistance changes in afferent and efferent arterioles
two types of nephrons?
superficial juxtamedullary (much longer loops of henle)
cortical nephron?
short loop of henle
-surrounded by peritubular capillaries
juxtamedullary nephron
long loop of henle
-long efferent arterioles divided into specialized peritubular capillaries (vasa recta)
renal microcirculation?
afferent arteriole
glomerular capillaries
efferent arteriole
peritubular capillaries
vasa recta
runs alongside loos of henle in juxtamedullary nephron
venous drainage?
interlobular vein
arcuate vein
interlobar vein
renal vein
first capillary network?
glomerular capillaries
- high hydrostatic pressure
- large fluid volume filtered in bowmans capsule
second capillary network?
peritubular capillarires
- low hydrostatic pressure
- law amounts of water and solute are reabsorbed
renal blood flow
very high flow
renal flow during exercise?
decreased flow
-blood is shunted to skeletal muscle
flow rates in regions of kidney?
cortex highest
slower as get more central (outer to inner medulla)
slow rate in medulla allows concentration of urine
innervation of kidney?
sympathetics on smooth muscle on arterioles and granular cells in afferent arterioles
granular cells
on juxtaglomerular apparatus
-sympathetic stimulation of renin release
sympathetic stimulation?
powerful constriction of afferent and efferent arterioles
-afferent > efferent
decreases renal blood flow
diverts renal fraction to vital organs
also stimulates renin release
renin
stimulates Na+ reabsorption in proximal tubule, thick ascending loop of henle, distal convoluted duct, collecting duct
glomerular filtration
filtration of plasma from glomerular capillaries into bowmans capsule
tubular reabsorption
transferral of substances from tubular lumen to peritubular capillaries
tubular secretion
transferral of substances from peritubular capillaries to tubular lumen
excretion
voiding of substances in urine
urinary excretion = ?
amount filtered - reabsorbed + secreted
tubular reabsorption = ?
glomerular filtration - urinary excretion
if excretion rate > filtration rate, tubular secretion must have occurred
glomerular filtration rate
volume of plasma filtered into combined nephron of both kidneys per unit time
filtration rate
GFR x plasma concentration of substance
urinary excrection rate?
flow rate x concentration of substance in urine
reabsorption or secretion of substance?
difference between glomerular filtration and urinary excretion (assuming substance is not produced or metabolized by kidneys)
excretion < filtration
net reabsorption occured
excretion > filtration
net secretion occured
clearance
volume of plasma from which a substance is completely removed by kidney in given time period
describes how effectively the kidneys remove a substance from the bloodstream and excrete it in the urine
different substances have different clearance
GFR measure depends on clearance
clearance of substance = ?
concentration in urine x urine volume /
concentration of substance in plasma
Cx = Ux x V / Px ***
GFR estimate?
can be done using clearance
-if compound freely filtered, but NOT secreted, reabsorbed, produced, nor degraded by the kidneys
inulin
freely filtered, not reabsorbed, secreted, or metabolized
inulin clearance equal to GFR
problems - need to inject it
creatinine?
another estimate of GFR
-freely filtered, but not perfect
creatinine secretion in proximal tubule overestimates Ux; substances in blood cause overestimation of Px
two sources of error nearly cancel eachother out
P-creatinine and GFR?
plasma creatinine
inversely proportional
not perfect, difference in lean muscle
compensatory increased proximal tubule secretion
uses of creatinine?
long term function
BUN/creatinine
creatinine from muscle
BUN from liver (waste product)
urea reabsorbed by tubules can be regulated
creatinine reabsorbed remains the same
BUN/Cr >20/1
prerenal problem
- BUN reabsorption is increased
- due to hypovolemia
creatinine doesn’t change with hypovolemia
BUN/Cr 10-20/1
normal range or postrenal
-can be postrenal disease (obstruction)
BUN/Cr <10/1
intrarenal
-renal damage causes reduced reabsorption of BUN and a lower BUN/Cr ratio
cystatin C
another marker of GFR
- produced by all nucleated cells
- freely filtered
- not dependent on muscle mass or gender
it goes up, GFR goes down
used to determine estimage GFR (eGFR)
para-amino hippuric acid (PAH)
freely filtered and avidly secreted
-completely cleared from plasma of peritubular capillaries
gives estimate of blood flow
filtration fraction
renal plasma flow through the tubule
FF = GFR/RPF
RPF = renal plasma flow
increased FF
oncotic pressure of efferent arteriole increases
-facilitates reabsorption
