Renal Flashcards
What is the range of SBP where renal perfusion is maintained and auto-regulated?
80-180mmHg
What happens to renal blood flow in response to high systemic pressures?
Afferent vasoconstriction –> reduces renal blood flow and brings glomerular pressure back to baseline –> GFR is maintained.
What happens to renal blood flow in response to hypovolemia or hypotension?
Efferent arteriolar vasoconstriction by activation of the sympathoadrenal system, renin-angiotensin system, and vasopressin (ADH). –> maintains pressure in glomerular capillaries —> GFR maintained.
What is the function of the proximal tubule?
65-75% of ultra-filtrate reabsorption
Main function is sodium reabsorption
Secrete creatinine and antibiotics
What is the function of the loop of henle?
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.
Which mineral is largely reabsorbed in the distal tubule?
parathyroid hormone and vitamin D-mediated CALCIUM reabsorption
Where is the main site of action for anti-diuretic hormone in the kidney?
Collecting duct
What is the relationship between serum creatinine and GFR?
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
What clinically available measure is a surrogate for glomerular filtration rate?
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.
What are the expected values for FENa (fractional excretion of sodium) calculation in hypovolemic and ATN states, respectively?
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
When might calculating FEUrea be helpful and what values correlate with hypovolemia and ATN?
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
Describe the effects of ionization and lipophilicity on drug reabsorption.
Non-Ionized drugs = reabsorbed
Highly lipophilic = reabsorbed and have virtually no renal clearance
Describe the tubuloglomerular feedback system
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.
What leads to low UOP during laparoscopic hysterectomy?
Inc in plasma [renin]
What is the site of action of acetazolamide and what effect does it have on the pH of the urine?
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.
How do osmotic diuretics place patients at risk for pulmonary edema?
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.
What electrolyte abnormalities frequently result from administration of loop diuretics?
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.
Where is the site of action of the thiazide diuretics and some of its side effects?
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
What is the mechanism of action of spironolactone?
mineralocorticoid receptor antagonist in DCT and CD
hyperkalemia
metabolic acidosis
gynecomastia and hirsutism d/t affinity of mineralocorticoid antagonists for progesterone and androgen receptors.
What are some of the side effects of loop diuretics?
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.
What receptors does high-dose dopamine activate that are not activated by fenoldopam?
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.
What fraction of total body weight is water and how is it distributed?
60% of the total body weight is water
intravascular (5% of total body water)
intracellular (60%)
interstitial (35%) compartments
What is the primary hormone that decreases urine free water secretion in response to hyperosmolality?
antidiuretic hormone (arginine vasopressin (AVP))
What stimulates arginine vasopressin (AVP) release?
Baroreceptors in the carotid sinus and aortic arch
Summarize the primary hormonal response to hypotension and hyponatremia.
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
What stimulates atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) release?
Atrial stretch = ANP
ventricular tension = BNP
What is the mechanism of action of aldosterone?
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
