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Renal medicine > Physiology of renal medicine > Flashcards

Physiology of renal medicine Flashcards

1
Q

How many litres do the kidneys filter in 24 hours in health?

A

180L

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2
Q

How much urine is produced per day?

A

1.5-2L

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3
Q

How is urine formed?

A

Capillary hydrostatic pressure forcing the water and salts of plasma across the glomerular basement membrane.

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4
Q

What molecules are freely filtered into the nephron?

A

<12,000 Da

-Electrolytes, sugars, AAs and vitamins

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5
Q

What factors affect the filtration of a molecule across the glomerular basement membrane?

A

Molecular weight, surface charge (GBM -ve charge, albumin is -ve charged), hydrostatic pressure in the afferent arteriole

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6
Q

What is the capillary hydrostatic pressure in the glomerulus?

A

45mmHg

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7
Q

What is the hydrostatic pressure in Bowman’s space?

A

10mmHg

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8
Q

What is the plasma protein oncotic pressure in the Bowmans capsule?

A

25mmHg

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9
Q

What is GFR and how is it accurately measured?

A

An exact measure of kidney function. Accurate measurement requires the injection of technetium 99. Only really performed on live kidney donors.

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10
Q

What is the alternative to GFR?

A

Creatinine clearance. Creatinine is released from muscle at a relatively constant rate. Filtered by the kidneys - some secretion into the filtrate by the proximal tubule, not as accurate, rarely used in clinical practice.

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11
Q

What is serum creatinine?

A

Released by muscle and removed by kidneys. Accumulates in kidney disease. Normal range: 64-104.

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12
Q

What is eGFR?

A

Requires: age, sex, ethnicity and serum creatinine. Correlates with the % of kidney function eg eGFR of 50=50% kidney function.

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13
Q

At what eGFR will patients need dialysis?

A

10

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14
Q

At what level is plasma osmolarity maintained?

A

285 mOsm/L

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15
Q

What is normal urine osmolarity?

A

50-1400 mOsm/L

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16
Q

How does ADH work?

A

Inserts channels into collecting duct to allow reabsorption of water.

17
Q

In a state of acute fluid loss there is increased secretion of:

A

ADH and renin

18
Q

An acutely ill patient with kidney disease is at higher risk of:

A

Hyperkalaemia, acidaemia, uraemia and fluid imbalance

19
Q

What is the Na/K ATPase pump?

A

Powerhouse. Lies on the apical surface of the tubule. Generates a potential energy gradient across the cell. Allows the recovery of many substance from the glomerular filtrate.

20
Q

What are the features of the proximal convoluted tubule?

A

Recovers 70% of glomerular filtrate - water and electrolytes

Recovery and generation of bicarb.

Low energy cost - 5% of total energy.

21
Q

What are the features of bicarb regeneration?

A

Dependent upon carbonic anhydrase (inhibited by acetazolamide).

Failure to regenerate in kidney disease results in acidaemia.

22
Q

What is taken up in the ascending loop of Henle?

A

Na, K, Cl and water.

23
Q

What is the site of action of loop diuretics?

A

Ascending loop of Henle (eg furosemide)

24
Q

What are the features of the cortical collecting duct?

A

Site of reabsorption of: Na+water in exchange for K. Controlled by aldosterone.

Site of action of aldosterone anatagonists - spironalactone.

25
Q

What is spironalactone?

A

K-sparing diuretic. High risk of hyperkalaemia.

26
Q

What are the features of the medullary collecting duct?

A

Site of urinary concentration.

ADH acts to increase water reabsorption.

27
Q

What is diabetes insipidus?

A

Central failure to secrete ADH or peripheral resistance to ADH, Polyuria, hypovolaemia and hyponatraemia.

28
Q

What is the site of action of osmotic diuretics?

A

Glomerulus.

29
Q

What is the site of action of carbonic anhydrase inhibitors?

A

DCT and PCT - inhibits carbonic anhydrase.

30
Q

What is the site of action of Thaizides?

A

DCT - sodium pump.

31
Q

What is the site of action of loop diuretics?

A

Ascending loop of Henle.

32
Q

What is the site of action of Spironalactone and amiloride?

A

Cortical collecting duct.

33
Q

What are possible treatments for hyperkalaemia?

A

Calcium gluconate

Insulin/glucose

dialysis

Renal medicine (9 decks)

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