Renal Excretory Function Flashcards
Glomerular filtration
180L of plasma filtered every day
1-2L urine produced
Factors that determine filtrate
Net filtration pressure Podocyte slit pores Size of molecule Charge of molecule --> -ve charge of GBM glycoproteins
Filtration at Glomerulus
Free movement of small solutes/molecules --> water, electrolytes (Na, K, Cl, phosphate, glucose). urea, amino acids Restriction of larger solutes/proteins --> MW cut off of 5200 daltons --> MW of albumin is 69,000 daltons
GFR
Total amount of fluid that is filtered through the glomerulus of both kidneys
180L/day
120ml/min
Clearance of substance
Creatinine clearance
Breakdown product of creatine phosphate (found in muscle)
Freely filtered in glomerulus
Secreted by peritubular capillaries –> creatinine clearance overestimates actual GFR by 10-20%
Creatinine clearance formula
(Urine Cr conc x Urine vol per min)/ Plasma Cr conc
To measure clearance of substance, have to
Measure conc. of creatinine in plasma
Collect urine for fixed period to get urine flow (ml/min)
Measure conc. of creatinine in collected urine
GFR measurements all methods
Creatinine clearance –> 24hr urine collection
Nuclear medicine scan (gold standard)
Estimated GFR- MDRD equation
4 variables in MDRD equation
Creatinine
Age
Gender
Ethnicity
Creatinine GFR Muscular individuals
Creatinine produced by muscle –> muscular individuals have naturally raised serum creatinine
–> eGFR underestimates true GFR
Creatinine GFR Malnourished individuals
Low serum creatinine
eGFR over estimates true GFR
Trimethoprin
Inhibit tubular secretion of creatinine
–> raised plasma creatinine even though GFR may be unchanged
Tight junction
Limits water + solute movement between cells
Secondary active transport
Use energy from non-ATP sources i.e. electrochemical gradients
Maintenance of interstitial Na conc
Use of active transportation
Primary active transport
Use ATP as energy source to drive movement
e.g. Na/K ATPase
Cystinuria
Autosomal recessive
Proximal tubule
Apical Na/cystine cotransporter
Abnormal cystine excretion
Renal glycosuria
Proximal tubule
Apical Na/glucose cotransporter
Abnormal urinary glucose loss
Happens despite normal/low blood flow
Proximal RTA
Proximal tubule
Basolateral Na/HCO3 cotr.
Type 2 renal tubular acidosis
Bartter type 1
Thick ascending loop of Henle
Apical Na/K/2Cl co transporter
Mimic effects of furosemide
–> hypokalaemia, metabolic alkalosis, hypocalcaemia, hypomagnasaemia
Gitelman’s
Distal tubule
Apical Na-Cl cotransporter
Mimic thiazide use
–> hypokalaemia, metabolic alkalosis, hypomagnesaemia, hypercalcaemia
Proximal tubule anatomy
Apical brush border (microvilli), large SA
1st 2/3- proximal convoluted tubule
Final 3rd- proximal straight tubule
Proximal tubule function
Bulk of reabsorption of solutes- up to 80%
Water- up to 65%
Amino acids, low molecular weight proteins- up to 100%
Loop of Henle aim
Reduce volume of water + solutes within urine but without changing concentration
–> creates hypertonic medulla
