Renal physiology

Question 1

What is the most common cause of AKI?

Answer 1

acute tubular necrosis
Necrosis of renal tubular epithelial cells severely affects the functioning of the kidney

Question 2

What are the two main causes of acute tubular necrosis?

Answer 2

Ischaemia
- shock
- sepsis

Nephrotoxins
- aminoglycosides
- myoglobin secondary to rhabdomyolysis
- radiocontrast agents
lead

Question 3

What feature may be found in microscopy in acute tubular necrosis?

Answer 3

Muddy brown casts

Question 4

What are the phases of acute tubular necrosis?

Answer 4

Phases of ATN
oliguric phase
polyuric phase
recovery phase

Question 5

What histological features do you find on ATN?

Answer 5

Tubular epithelium necrosis: loss of nuclei and detachment of tubular cells from the basement membrane
Dilatation of the tubules may occur
Necrotic cells obstruct the tubule lumen

Question 6

How does the kidney control blood flow?

Answer 6

the kidney is able to autoregulate its blood flow between systolic pressures of 80-180mmHg so there is little variation in renal blood flow
this is achieved by myogenic control of arteriolar tone, both sympathetic input and hormonal signals (e.g. renin) are responsible
renal cortical blood flow > medullary blood flow (i.e. tubular cells more prone to ischaemia)

Question 7

What is the purpose of the basement membrane of the golmerulus being negatively charged?

Answer 7

larger negatively charged molecules such as albumin are unable to cross

Question 8

Due to the structure of the glomerulus, what does this do to the “forces”?

Answer 8

considerable hydrostatic pressure

Question 9

How is glomerular filtration rate calculated?

Answer 9

(Concentration in glomerular filtrate X volume of urine per minute) / serum concentration

Question 10

Why is creatinine used as a marker for estimated glomerular filtration?

Answer 10

Subjected to little proximal convoluted tubule secretion

Question 11

What is the function of the proximal convoluted tubule?

Answer 11

proximal tubule substrates such as glucose, amino acids and phosphate are co-transported with sodium across the semi permeable membrane
up to two thirds of filtered water is reabsorbed in the proximal tubules

Question 12

What is the function of the thin ascending limb of the loop of henle?

Answer 12

the thin ascending limb is impermeable to water, but highly permeable to sodium and chloride ions
At the end of the thin limb fluid is HYPOosmotic

Question 13

What is the function of the thick ascending limb of the loop of henle?

Answer 13

As fluid if hypoosmitic at the end of the thin limb. The thick ascending limb the reabsorption of sodium and chloride ions occurs by both facilitated and passive diffusion pathways

Question 14

What does red cell casts suggest?

Answer 14

Glomerulonephritis
Renal ischaemia and infarction

Question 15

What does white cell casts suggest?

Answer 15

Acute pyelonephritis
Interstitial nephritis

Question 16

What does granular casts suggest?

Answer 16

Acute tubular necrosis

Question 17

What does hyaline casts suggest?

Answer 17

Common and non-specific
May be seen following exercise or dehydration

Question 18

What does epithelial casts suggest?

Answer 18

Acute tubular necrosis

Question 19

What does waxy casts suggest?

Answer 19

Advanced chronic kidney disease

Question 20

What does fatty casts suggest?

Answer 20

Nephrotic syndrome

Question 21

What type of kidney stones does proteus cause?

Answer 21

Struvite

Question 22

What red cell morphology in urine suggests glomerular pathology

Answer 22

dysmorphic