Renal

Question 1

What is the range of SBP where renal perfusion is maintained and auto-regulated?

Answer 1

80-180mmHg

Question 2

What happens to renal blood flow in response to high systemic pressures?

Answer 2

Afferent vasoconstriction –> reduces renal blood flow and brings glomerular pressure back to baseline –> GFR is maintained.

Question 3

What happens to renal blood flow in response to hypovolemia or hypotension?

Answer 3

Efferent arteriolar vasoconstriction by activation of the sympathoadrenal system, renin-angiotensin system, and vasopressin (ADH). –> maintains pressure in glomerular capillaries —> GFR maintained.

Question 4

What is the function of the proximal tubule?

Answer 4

65-75% of ultra-filtrate reabsorption
Main function is sodium reabsorption
Secrete creatinine and antibiotics

Question 5

What is the function of the loop of henle?

Answer 5

Maintaining a hypertonic medullary interstitium and indirectly provides the collecting ducts with the ability to concentrate urine.

The thick portion of the ascending limb (mTAL segment) is impermeable to water

site for calcium and magnesium reabsorption.

Question 6

Which mineral is largely reabsorbed in the distal tubule?

Answer 6

parathyroid hormone and vitamin D-mediated CALCIUM reabsorption

Question 7

Where is the main site of action for anti-diuretic hormone in the kidney?

Answer 7

Collecting duct

Question 8

What is the relationship between serum creatinine and GFR?

Answer 8

Normal Cr = 0.7-1.2 mg/dL.

[Cr] depends on total body water, muscle mass, catabolic rate, and GFR, thus it may over- or under-estimate renal dysfunction.

The relationship b/w serum Cr and GFR is inverse and exponential = doubling of the serum Cr = halving of the GFR

Question 9

What clinically available measure is a surrogate for glomerular filtration rate?

Answer 9

Creatinine Clearance (CCr)

CCr = [140 minus age in years][body weight in kg]/[serum Cr x 72].

Normal = 110-150 ml/min
Women = derived value is multiplied by 0.85

When serum Cr is rapidly changing and in obese, edematous, or cachectic patients, there are limitations to this calculation.

Question 10

What are the expected values for FENa (fractional excretion of sodium) calculation in hypovolemic and ATN states, respectively?

Answer 10

FENa = (urine sodium/serum sodium)/(urine Cr/serum Cr) x 100%.

In hypovolemic states, the FENa is 3%.

Diuretic medications alter the accuracy of the FENa –> tend to increase the FENa

Question 11

When might calculating FEUrea be helpful and what values correlate with hypovolemia and ATN?

Answer 11

When diuretics are used

FEUrea= ( UUrea × PCr ) / ( UCr × PUrea ) × 100%.

Pre-renal = FEUrea 55-60%
Normal = FEUrea of 35-50%

FEUrea has a higher positive predictive value (PPV) in separating prerenal syndrome from ATN

Question 12

Describe the effects of ionization and lipophilicity on drug reabsorption.

Answer 12

Non-Ionized drugs = reabsorbed

Highly lipophilic = reabsorbed and have virtually no renal clearance

Question 13

Describe the tubuloglomerular feedback system

Answer 13

distal tubule detects and responds to an increase in Cl- delivery to the macula densa.

Release of renin –> conversion of angiotensinogen (liver) –> angiotensin I

Angiotensin Converting Enzyme (ACE) –> Angiotensin I –> Angiotensin II –>renal vasoconstriction directly + through activation of SNS

Angiotensin II –> release of aldosterone –> Na reabsorption, K excretion and water retention

Finally, Angiotensin II –> (Arginine Vasopressin) AVP secretion –> water absorption.

Question 14

What leads to low UOP during laparoscopic hysterectomy?

Answer 14

Inc in plasma [renin]

Question 15

What is the site of action of acetazolamide and what effect does it have on the pH of the urine?

Answer 15

proximal tubule –> Inhibition of carbonic anhydrase –> decrease reabsorption of sodium and bicarbonate –> alkalinized urine.

Mild systemic metabolic acidosis

Used to make alkaline urine
Treat of altitude sickness and open-angle glaucoma.

Question 16

How do osmotic diuretics place patients at risk for pulmonary edema?

Answer 16

Increase blood osmolarity and draw water into the intravascular space –> increasing renal blood flow

Acute pulmonary edema - patients with poor cardiac reserve from the acute increase in intravascular volume associated with an osmotic diuretic bolus.

Question 17

What electrolyte abnormalities frequently result from administration of loop diuretics?

Answer 17

inhibit the sodium-potassium-chloride symporter in the thick ascending limb of the loop of Henle

Decreased water reabsorption + excretion of sodium, potassium, chloride, calcium, magnesium and hydrogen

INC systemic venous capacitance –> reduce LVEDP in patients in left ventricular failure

The effectiveness of loop diuretics is reduced in patients taking them chronically as well as in combination with anticonvulsants.

Question 18

Where is the site of action of the thiazide diuretics and some of its side effects?

Answer 18

Inhibits the sodium-chloride symporter in the distal convoluted tubule –> preventing the reabsorption of sodium and chloride

hypokalemia
hyponatremia
hypercalcemia
metabolic alkalosis
hyperuricemia
hyperglycemia
increased LDL cholesterol

Question 19

What is the mechanism of action of spironolactone?

Answer 19

mineralocorticoid receptor antagonist in DCT and CD

hyperkalemia
metabolic acidosis
gynecomastia and hirsutism d/t affinity of mineralocorticoid antagonists for progesterone and androgen receptors.

Question 20

What are some of the side effects of loop diuretics?

Answer 20

hyponatremia
hypokalemia
hyperuricemia
hyperglycemia
increase in LDL cholesterol

Ototoxicity can occur with rapid administration.

Increase the quantity of non-albumin bound warfarin and clofibrate –> increasing effects.

Question 21

What receptors does high-dose dopamine activate that are not activated by fenoldopam?

Answer 21

alpha and beta

Fenoldopam = DA1 agonist –> decreases arterial tone –> vasodilation of renal arteries

may be renoprotective during cardiac surgery. SE = headache, flushing and reflex tachycardia.

Question 22

What fraction of total body weight is water and how is it distributed?

Answer 22

60% of the total body weight is water
intravascular (5% of total body water)
intracellular (60%)
interstitial (35%) compartments

Question 23

What is the primary hormone that decreases urine free water secretion in response to hyperosmolality?

Answer 23

antidiuretic hormone (arginine vasopressin (AVP))

Question 24

What stimulates arginine vasopressin (AVP) release?

Answer 24

Baroreceptors in the carotid sinus and aortic arch

Question 25

Summarize the primary hormonal response to hypotension and hyponatremia.

Answer 25

glomerulus senses low sodium flow due to hypovolemia –> renin –> converts angiotensinogen (produced by the liver) to angiotensin I (AT-I)

AT-I is converted to AT-II in the lung –> increasing SVR, + stimulating release of aldosterone from the zona glomerulosa of the adrenal cortex

Question 26

What stimulates atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) release?

Answer 26

Atrial stretch = ANP

ventricular tension = BNP

Question 27

What is the mechanism of action of aldosterone?

Answer 27

upregulates and activates the Na+/K+ pumps in the distal tubule and collecting duct

Stimulates distal tubule cells to synthesize

(1) bicarbonate
(2) sodium channels –> sodium and water reabsorption