20. Renal Clearance Flashcards
What are some symptoms of kidney disease?
Hypertension
Oedema
Haematuria
May be asymptomatic
What are the 3 processes involved in urine formation?
Ultrafiltration
Reabsorption
Secretion
What is renal clearance?
ml of plasma cleared of a substance in one min
Cs= mL/min
What is the clearance formula?
Cs= (Us x V) /Ps U= conc in urine V= vol excreted/min P= conc in plasma
What qualities would a substance used to measure GFR require?
Freely filtered Not reabsorbed Not secreted Not metabolism by tubular cells Not toxic Easily measured
What substances can be used to measure GFR?
Inulin
Creatinine
Why is inulin not used to measure GFR?
Does not occur naturally in the body
What are the normal clearance values for inulin or creatinine?
120ml/min
What is the Crockroft and Gault relationship?
Used to calculate creatinine clearance
(140-age)x weight / 72 x serum creatinine
Multiply by .85 in females
What does it mean if a substance has a lower clearance than inulin?
The substance is filtered and reabsorbed
Eg. glucose, urea
What does it mean if a substance has a greater clearance than inulin?
Filtered and secreted
Eg. PAH
What is used to measure renal plasma flow?
PAH
All PAH that escapes from filtration is secreted back in, so all PAH is completely removed from plasma that flows through kidneys
What is normal effective renal plasma flow?
625 ml/min
What does it mean if a substance is freely filtered, not absorbed and not secreted?
Renal clearance= normal GFR
Eg. Inulin
What does it mean if a substance is freely filtered, fully absorbed and not secreted?
Renal clearance= 0ml/min
Eg. glucose, AAs
What does it mean if a substance is freely filtered, not absorbed and fully secreted?
Renal clearance= eRPF
Eg. PAH
What does it mean if a substance is freely filtered, slightly absorbed and not secreted?
Renal clearance < GFR
Eg. Urea
What is renal failure?
Reduction in GFR so that kidneys can no longer maintain salt and water balance or excrete nitrogenous waste products
What are the causes of acute renal failure?
Altered blood supply
Damage due to toxins or inflammation
Urinary tract abnormalities
What are the consequences of acute renal failure?
Salt and water retention K+ retention Metabolic acidosis Hyperphosphataemia Increased plasma urea and creatinine
What are the causes of chronic renal failure?
Metabolic disorders Renal vascular disorders Immunological disorders Infection Urinary tract obstruction Congenital disorders
What are the consequences of chronic renal failure?
Inability to concentrate or dilute urine Water retention Increase in urea and creatinine Anaemia Acid and ion imbalances Osteomalacia Secondary hyperparathyroidism
