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20 Cards in this Set

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What would be the result when there is a reduction of functional nephrons to 25% of normal?
The surviving nephrons must excrete 4X as much sodium and 4X as much volume as normal to maintain water and electrolyte balance. This rapid flow of urine will decrease their ability to adequately concentrate urine.
Regarding the above dilemma, how would urinary sodium be effected?
Urinary sodium excretion would be maintained at normal levels, equal to intake, through various compensatory mechanisms(increased arterial pressures). Increased creatinine plasma conc. in body fluids would occur.
Aldosterone stimulates potassium secretion by the principal cells of the collecting tubules. TRUE/FALSE
TRUE. Blockade of the action of aldosterone with spironolactone(K+ sparer diuretic) would inhibit K+ secretion.
If a patient has a creatinine clearance of 90ml/min, a urine flow rate of 1ml/min, a plasma K+ concentration of 4mEq/L, and a urine K+ concentration of 60mEq/L, what is the app. rate of K+ excretion?
K+ excretion rate= urine K+ concentration(60 mEq/L) X urine flow rate(0.001L/min)= 0.06mEq/min.
Is there an increase in urine volume in the absence of ADH?
Yes. The late distal and collecting tubules are relatively impermeable to water. As a result, there is dehydration and increaqsed plasma osmolarity and high plasma sodium concentration.
This decrease in ECF volume stimulates renin secretion, resulting in an increase in plasma renin concentration.
In a patient with a very high rate of renin secretion, there would also be increased formation of angiotensin 11. TRUE/FALSE
TRUE. This would as well stimulate aldosterone secretion. increased levels of angiotensin 11 and aldosterone would cause a transient decrease in Na+ excretion, which woulld cause expansion of the ECF volume, with increased arterial pressure.
What effect would increased levels of aldosterone have on potassium?
It would cause hypokalemia, where high levels of angiotensin 11 would cause renal vasoconstriction and decreased renal blood flow.
Impairment of proximal tubular NaCl reabsorption, would increase NaCl delivery to the macula densa. TRUE/FALSE
TRUE. This would in turn cause a tubuloglomerular feedback mediated increase in afferent arteriolar resistance. This would decrease the glomerular filtration rate. Initially there would be a transient increase in sodium excretion.
What roles do renal prostaglandins play?
They play an important role in preventing excessive vasoconconstriction of afferent arterioles and decreased GFR, especially under conditions of volume depletion.
Administration of a thiazide diuretic would tend to cause volume depletion and addition of a nonsteroidal anti-inflammatory drug would inhibit the formation of vasodilator prostaglandins, causing increased afferent arteriolar resistance and decreased GFR. TRUE/FALSE
TRUE.
What occurs when potassium intake is doubled?
When it is doubled from 80 to 160mmol/day, K+ excretion also app. doubles within a few days. This is acheived largely by increased secretion of potassium in the cortical collecting tubule. It is also acheived by increased aldosterone secretion.
An 8 year old boy is brought to the doctors office with extreme swelling of the abdomen. His parents said that he had a "very sore throat" a month or so ago and that he has been sweeling up since. He appears to be edematous, and a U/A reveals large amounts of protein being excreted. A temporary diagnosis of nephrotic syndrome subsequent to glomerulonephritis is made. What explanation might justify this condition?
This patient has proteinuria and reduced plasma protein concentration secondary to glomerulonephritis caused by untreated strep infection. The reduced plasma protein concentration has decreased the plasma colloid osmotic pressure and resulted in leakage from the plasma to the interstitium. There is as a result increased lymph flow, and this causes a washout of interstitial fluid protein as a safety factor against edema. If blood pressure is lowered for obvious reasons, renin is secreted.
A 32 year old man complains of frequent urination. He is overweight(280#s, 5 ft 10 inches tall, and after measuring the 24 hour creatinine clearance, you estimate his glomerular filtration rate(GFR) to be a 150ml/min. His plasma glucose is 300mg/dl. Assuming his renal transport maximum for glucose is normal,what would be this patients app rate of urinary glucose excretion?
The filtered load of glucose in this example is determined as follows:
GFR(150ml/min) X plasma glucose(300mg/dl) = 450mg/min. The transport maximum for glucose here is 300mg/min.
Therefore, the maximum rate of glucose absorption is 300mg/min. The urinary glucose excretion is = to the filtered load(450mg/min) minus the tubular reabsorption of glucose(300mg/min) or 150 mg/min.
What does one expect to see in respiratory acidosis?
A patient has resp. acidosis when the plasma pH is lower than the normal level of 7.4 and the plasma PCO2 is higher than the normal level of 40mmHg. Occasionally, an elevation of plasma bicarbonate is seen(about 24mEq/L), and this due to partial renal compensation for the respiratory acidosis.
Peritubular capillary fluid reabsorption is determined by the balance of hydrostatic and colloid osmotic forces in the peritubular capillaries. TRUE/FALSE
TRUE.
Inhibition of aldosterone causes hyperkalemia by two mechanisms. What are they?
1. Shifting K+ out of the cells into the extracellular fluid
2. Decreasing cortical collecting tubular secretion of potassium.
What is Amiloride?
It is a diuretic that inhibits sodium reabsorption in the collecting ducts.
The filterability of solutes in the plasma is inversely related to what?
It is inversely related to the size of the solute(molecular weight). Also, positively charged molecules are filtered more readily than are neutral or negatively charged molecules of equal molecular weight.
Ex: the positively charged polycationic dextran with a mol. wt. of 25,000 would be a very readily filtered substance. RBCs are not filtered at all.
App. how much urea is reabsorbed in the proximal tubule?
App. 30-40% of filtered urea is reabsorbed. Urea conc. increases further in the tip of the loop of Henle because water is reabsorbed in the descending limb of the loop of Henle. Under conditions of antidiuresis, urea is further concentrated as water is reabsorbed and as fluid flows along the collecting ducts.
Excessive activity of the amiloride sensitive sodium channel in the collecting tubules would cause a transient decrease in sodium excretion and expansion of ECF volume, which would increase arterial pressure. TRUE/FALSE
TRUE.