16.8 Physiology: The pathophysiology of renal function

Question 1

What is the definition of acute renal failure?

Answer 1

Occurs suddenly, urine flow less than 500mL/day

Question 2

What is the definition of chronic renal failure?

Answer 2

Occurring gradually over 6 months, GFR

Question 3

What is a lab test marker of chronic renal failure?

Answer 3

Specific gravity of 1.010

Question 4

What is loss of GFR invariably accompanied by? (2)

Answer 4

Impairment of tubular processes- reabsorption and secretion

Question 5

What can GFR loss be due to?

Answer 5

Glomerular or tubular disease

Question 6

In CRF, what kind of endocrine impairment can occur?

Answer 6

RAS

Vit D activation

Erythropoeitin

Question 7

What predictably increases in concentration in chronic kidney disease?

How much of it is normally reabsorbed?

Answer 7

Urea (50%)

-but not so reliable, can occur in situations other than CRF

Question 8

Why can we use creatinine to assess GFR?

Answer 8

Production is constant, it is not reabsorbed

Question 9

What is the formula for creatinine clearance? What is a normal range?

Answer 9

UV/P=GFR

P: 50-120uM/L

Question 10

What is daily production (and excretion) of creatinine proportionate to?

Answer 10

Muscle mass

GFR inversely proportional to plasma creatinine concentration

Question 11

What is the net filtration pressure equal to?

Answer 11

10mm Hg

Question 12

Which is the most common cause of acute renal failure?

Answer 12

Pre-renal (e.g. shock, haemorrhage, dehydration)

Question 13

What are some pre-renal causes of ARF? (5) When does it occur?

Answer 13

Systemic perfusion pressure

Question 14

What causes intrinsic acute renal failure? (3)

Answer 14

Glomerular disease, interstitial nephritis, tubular damage (ischaemia or toxins)

Question 15

What is the most common cause of renal origin ARF?

What are 3 features?

Answer 15

Acute tubular necrosis

Oliguria
+/- acidosis and increase in K+

Question 16

What is a cause of post-renal ARF?

Answer 16

Outlet obstruction (ureteric, cystic or urethral; stones, clots, fibrosis, tumours)

Question 17

What happens to the remaining nephrons in CRF?

What happens to the glomeruli?

Answer 17

Hypertrophy

Hyperfiltration and hypertension–>glomerulosclerosis

Question 18

When is uremia symptomatic? What can it result in?

Question 19

What are some common causes of CRF?

Answer 19

Diabetes, high blood pressure, chronic glomerulonephritis, cystic disease

Question 20

What are the differences in CRF salt and water imbalances for predominantly glomerular or tubular disease?

Answer 20

Glomerular:
Sodium retention and hypertension

Tubular:
Sodium wasting, low BP, impaired ability to concentrate and polyuria

Question 21

What happens with potassium and pH in CRF?

Answer 21

K+
-Tends to rise, higher in diabetes

pH
-falls (H+ accumulates), failure to excrete non-volatile acids

Question 22

What happens with calcium and PO4 in CRF?

Answer 22

Rise in PO4, reciprocal reduction in Ca

Question 23

Why does renal osteodystrohpy occur?

Answer 23

Low Vit D3 (reduced Vit D activation, hyperphosphatemia, renal rickets)

High PTH (excessive osteoclastic activity)