W3: Kidneys Flashcards
2 main parts of kidney
glomerulus
tubule
6 kidney functions
- reg vol of fluid in blood
- electrolyte balance
- acid-base balance
- excretion of waste prods
- vit D metabolism
- prod of erythropoietin
3 waste products that kidneys excrete
- creatinine (from skeletal muscle)
- urea
- uric acid
what component filters the fluid?
Bowman’s/ glomerular capsule
2 renal function tests
- GFR (glomerular filtration rate
- measurement of waste prods in plasma
what does GFR measure
vol of fluid filtered through all glomeruli per time unit
normal GFR
60-120ml/ min
what is eGFR + what’s it based on
estimated glomerular filtration rate
based on an equation validated against gold standard renal clearance test
normal eGFR
> 90ml/ min
what does decreasing eGFR indicate
impairment of renal function
2nd renal function test?
measurement of waste prods in plasma e.g creatinine + urea
problem of using creatinine as measure of renal function
not a sensitive marker of renal function - stays within normal ranges even when chronic renal disease already established
what is urea a waste prod of
protein + AA metabolism
problem w urea measuring for renal function? when may it be useful?
- poor indicator of renal function (influenced by protein metabolism, the state of dehydration + use of steroids)
- may be useful in elderly/ children w dehydration as starts to rise b4 creatinine - becomes more concentrated
how is acid-base balance maintained?
by renal:
- secretion of H+
- reabsorption of HCO3-
high [H+] w/out renal buffering causes?
metabolic acidosis
low [H+] w/out renal buffering causes?
metabolic alkalosis
2 renal function-related test that are indirectly affected in renal failure?
- plasma phosphate bc kidney involved in phosphate excretion
- plasma Ca2+ - bc kidney involved in active vit D prod
what may cause low calcium in ACUTE renal failure?
raised phosphate in plasma
what may cause low calcium in CHRONIC renal failure?
low 1,25 diOHvitamin D3
what does glomeruli damage cause?
protein to leak into tubules + they can’t reabsorb enough protein back into bloodstream
when small-middle sized proteins can’t be reabsorbed it can lead to?
albuminuria
as renal disease progresses bigger proteins get through leading to?
proteinuria
what particular renal condition shows considerable proteinuria?
nephrotic syndrome
what can cause acute onset of decr renal function?
- hypovolaemia secondary to blood loss, dehydration, shock
- glomerulonephritis
drugs affecting glomeruli/ tubules - rhabdomyolysis
- obstruction of renal blood/ urine flow
define glomerulonephritis
acute inflammatory process affecting glomeruli
define rhabdomyolysis
massive muscle breakdown
what does decr GFR in acute renal failure (RF) lead to?
rapid decr of urine vol
may show anuria (no urine output) in severe cases
how does acute renal failure (RF) affect waste prods
incr in waste prods e.g plasma urea + plasma creatinine
how does acute RF affect electrolytes
incr in electrolytes e.g plasma K+ + plasma phosphate
how does acute RF affect acids
incr as kidneys are not excreting them
how does acute RF affect plasma Na+
incr/ decr/ normal dpending on cause
usually decr due to H2O retention making plasma more dilute
muscle test determined based on quantity of which enzyme
creatine kinase
what can be present in urine indicating acute RF that is usually absent
myoglobin (toxic to kidneys)
creatine kinase high or low in acute RF + why
high bc leaks out into blood when skeletal tissue damaged
define chronic renal failure (CRF)/ chronic kidney disease (CKD)
GRADUAL decline of renal function over yrs
causes of CRF/ CDK
- diabetes (diabetic nephropathy)
- hypertension
- diseases affecting glomeruli/ tubules/ interstitium
abnormal if eGFR is
<60ml/ min
abnormal value range of GFR
60-90 w other features of CDK
why is creatinine not a good marker for CDK
only starts rising when >70% of renal function has been lost
how does CDK affect waste prods
incr in them:
- plasma urea
- plasma creatinine
how does CDK affect electrolytes
incr plasma K+ (late on)
incr plasma phosphate (late on)
what happens to plasma Ca+ in CDK + why
normal or decr due to decr active vit D prod
what hormones affect Na+, H2O & K+
adrenals: renin/ angiotensin/ aldosterone axis
what hormone only affects H2O
post pit: ADH/ AVP
define hyponatraemia
[Na+] in your blood is abnormally low and/ or excess H2O
why is hyponatraemia important
can dilute conc of ions a lot
define hypernatraemia
incr [Na+]
usually due to loss of H2O
rarely bc excess Na+
why is hypernatremia important
water drawn out of cells by osmosis, cells get smaller
acidosis usually associated w incr or decr serum K+?
incr
alkalosis usually associated w incr or decr serum K+?
decr
value for hyperkalaemia
plasma K+ >5.5 mmol/L
causes of hyperkalaemia
- artefacts: haemolysis, cold weather, delayed sample processing, high platelets
- incr intake of K+
- incr renal reabsorption
- decr loss e.g. chronic/ acute RF
why is hyperkalaemia important
changes to heart rhythm (arrhythmia)
value for hypokalaemia
plasma K+ < 3.5 mmol/L
causes of hypokalaemia
- artefacts: hot weather during blood storage
- decr intake of K+
- decr renal reabsorption
- incr loss: vomiting/ diarrhoea / kidneys
why is hypokalaemia important
changes to heart rhythm (arrhythmia)
muscle weakness
