20. Renal Clearance

Question 1

What are some symptoms of kidney disease?

Answer 1

Hypertension
Oedema
Haematuria
May be asymptomatic

Question 2

What are the 3 processes involved in urine formation?

Answer 2

Ultrafiltration
Reabsorption
Secretion

Question 3

What is renal clearance?

Answer 3

ml of plasma cleared of a substance in one min

Cs= mL/min

Question 4

What is the clearance formula?

Answer 4

Cs= (Us x V) /Ps
U= conc in urine
V= vol excreted/min
P= conc in plasma

Question 5

What qualities would a substance used to measure GFR require?

Answer 5

Freely filtered
Not reabsorbed
Not secreted
Not metabolism by tubular cells
Not toxic
Easily measured

Question 6

What substances can be used to measure GFR?

Answer 6

Inulin

Creatinine

Question 7

Why is inulin not used to measure GFR?

Answer 7

Does not occur naturally in the body

Question 8

What are the normal clearance values for inulin or creatinine?

Answer 8

120ml/min

Question 9

What is the Crockroft and Gault relationship?

Answer 9

Used to calculate creatinine clearance
(140-age)x weight / 72 x serum creatinine
Multiply by .85 in females

Question 10

What does it mean if a substance has a lower clearance than inulin?

Answer 10

The substance is filtered and reabsorbed

Eg. glucose, urea

Question 11

What does it mean if a substance has a greater clearance than inulin?

Answer 11

Filtered and secreted

Eg. PAH

Question 12

What is used to measure renal plasma flow?

Answer 12

PAH
All PAH that escapes from filtration is secreted back in, so all PAH is completely removed from plasma that flows through kidneys

Question 13

What is normal effective renal plasma flow?

Answer 13

625 ml/min

Question 14

What does it mean if a substance is freely filtered, not absorbed and not secreted?

Answer 14

Renal clearance= normal GFR

Eg. Inulin

Question 15

What does it mean if a substance is freely filtered, fully absorbed and not secreted?

Answer 15

Renal clearance= 0ml/min

Eg. glucose, AAs

Question 16

What does it mean if a substance is freely filtered, not absorbed and fully secreted?

Answer 16

Renal clearance= eRPF

Eg. PAH

Question 17

What does it mean if a substance is freely filtered, slightly absorbed and not secreted?

Answer 17

Renal clearance < GFR

Eg. Urea

Question 18

What is renal failure?

Answer 18

Reduction in GFR so that kidneys can no longer maintain salt and water balance or excrete nitrogenous waste products

Question 19

What are the causes of acute renal failure?

Answer 19

Altered blood supply
Damage due to toxins or inflammation
Urinary tract abnormalities

Question 20

What are the consequences of acute renal failure?

Answer 20

Salt and water retention
K+ retention
Metabolic acidosis
Hyperphosphataemia
Increased plasma urea and creatinine

Question 21

What are the causes of chronic renal failure?

Answer 21

Metabolic disorders
Renal vascular disorders
Immunological disorders
Infection
Urinary tract obstruction
Congenital disorders

Question 22

What are the consequences of chronic renal failure?

Answer 22

Inability to concentrate or dilute urine
Water retention
Increase in urea and creatinine
Anaemia
Acid and ion imbalances
Osteomalacia
Secondary hyperparathyroidism