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Flashcards in Renal Intro & Filtration Quiz Deck (17)
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1

The volume of the ultrafiltrate of plasma entering the tubules by glomerular filtration in 1 day is typically:

greater than the total body fluid volume.



A standard 70kg individual contains 42L of water (~60% total body weight), and filters as much as 180L plasma per day.

2

A substance known to be freely filtered has a certain concentration in the afferent arteriole. What can we predict about its concentration in the efferent arteriole?

close to the value in the afferent arteriole

3

If autoregulation is effective, we expect to see which one of the following held almost constant?

the filtered load of water and small ions

4

A 67-year-old woman involved in a motor vehicle accident lost 1L of blood because of an open fracture of her left femur. Paramedics were able to prevent further bleeding. What changes to her intracellular fluid (ICF) and extracellular fluid (ECF) volumes would be observed 15 minutes after this blood loss?

ECF volume smaller; ICF volume unchanged

5

The following pressure measurements were obtained from within the glomerulus of an experimental animal:

Glomerular capillary hydrostatic pressure = 50mmHgGlomerular capillary oncotic pressure = 26 mmHg
Bowman's space hydrostatic pressure = 8 mmHg
Bowman's space oncotic pressure = 0 mmHg

Calculate the glomerular net ultra filtration pressure (positive pressure favors filtration; negative pressure opposes filtration).

Using equation PUF = PGC - (πGC + PGC).
PUF = 50 - (26 + 8) = +16 mmHg (favoring filtration).

6

A novel drug aimed at treating heart failure was tested in experimental animals. The drug was rejected for testing in humans because it caused an unacceptable decrease in the glomerular filtration rate (GFR). Further analysis showed that the drug caused no change in mean arterial blood pressure but renal blood flow (RBF) was increased. The filtration fraction was decreased. What mechanism is most likely to explain the observed decrease in GFR?

efferent arteriole dilation

An increase in RBF without an increase in blood pressure indicates a decrease in renal vascular resistance. Dilation of the efferent arteriole increases glomerular capillary outflow and reduces PGC, causing GFR to decrease. Filtration fraction decreases because GFR is smaller and RBF is larger

7

If the clearance of a freely filtered substance is less than the clearance of inulin, then the the substance:

underwent net reabsorption

8

Diabetic nephropathy is associated with thickened glomerular capillary basement membranes. The decrease in glomerular filtration rate results from:

A reduction in the permeability of the glomerular filtration barrier.

9

The kidneys perform all the following functions EXCEPT:

production of aldosterone.

10

Renal blood flow (RBF) in a young man was detrmined to be 1 L/min. If his inulin clearance is 125 mL/min, and hematocrit is 0.4, what is his renal filtration fraction?

The correct answer is B. Filtration fraction is defined as the glomerular filtration rate (GFR) divided by the renal plasma flow (RPF). The renal plasma flow equals [RBF x (1-hematocrit)], or 600 mL/min. Because Cin is equated with the GFR, the filtration fraction is 125 mL/min ÷ 600 mL/min, or ~20%.

11

A patient taking penicillin for a bacterial infection presents with nausea and vomiting. Urinalysis reveals mild proteinuria and cell casts, suggestive of acute intersitial nephritis. Which of the following glomerular structures normally prevents cells from entering the tubule?

Capillary endothelial cells

Correct answer is C. The glomerular filtration barrier comprises capillary endothelial cells, a basemant membrane, and a filtration slit diaphragm located between podocyte foot processes. Capillary walls are fenestrated to enhance plasma filtration, but the pores are small (~70 nm), effectively trapping the cells in the vasculature. Smooth muscle cells are located in glomerular arterioles, whereas mesangial cells are located between the glomerular capillaries. Although the latter regulate barrier surface area, they are not directly involved in fluid filtration.

12

A 65-year-old man with a family history of nephrolithiasis presents with flank pain. A creatinine clearance assessment is performed. "Creatinine clearance" best equates with which of the following?

Plasma volume completely cleared of creatinine per minute

13

Urine flow rate = 1 ml/min
Urine inulin concentration = 100mg/ml
Plasma inulin concentration = 2 mg/ml
Urine urea concentration = 50 mg/ml
Plasma urea concentration = 2.5 mg/ml

What is the glomerular filtration rate (GFR)?

50 ml/min

14

Urine flow rate = 1 ml/min
Urine inulin concentration = 100mg/ml
Plasma inulin concentration = 2 mg/ml
Urine urea concentration = 50 mg/ml
Plasma urea concentration = 2.5 mg/ml

What is the net urea reabsorption rate?

The net urea reabsorption rate is equal to the filtered load of urea (GFR [50 ml/min] x plasma urea concentration [2.5 mg/ml] - urinary excretion rate of urea (urine urea concentration [50 mg/ml] x urine flow rate [1 ml/min]. Therefore, net urea reabsorption = (50 ml/min x 2.5 mg/ml) - (50 mg/ml x 1 ml/min) = 75 mg/min.

15

Which of the following solutions when infused intravenously would result in an increase in extracellular fluid volume, a decrease in intracellular fluid volume, and an increase in total body water after osmotic equilibrium?

1 liter of 3 per cent sodium chloride solution

A 3 per cent sodium chloride (NaCI) solution is hypertonic and when infused intravenously would increase extracellular fluid volume and osmolarity, thereby causing water to flow out of the cell. This would decrease intracellular fluid volume and further increase extracellular fluid volume. The 0.9 per cent NaCI solution and 5 per cent dextrose solution are isotonic and therefore would not reduce intracellular fluid volume. Pure water and the 0.45 per cent NaCI solution are hypotonic and when infused would increase both intracellular and extracellular fluid volumes.

16

Increases in both renal blood flow and glomerular filtration rate (GFR) are caused by which of the following?

Dilation of afferent arterioles

Dilation of afferent arterioles increases glomerular hydrostatic pressure, which in turn increases GFR, decreases total renal vascular resistance, and increases renal blood flow. Dilation of efferent arterioles increases renal blood flow but reduces glomerular hydrostatic pressure and therefore tends to reduce GFR. Increased glomerular capillary filtration coefficient would increase GFR but has no direct effect on renal blood flow. Increases in plasma colloid osmotic pressure or renal sympathetic nerve activity would tend to reduce GFR.

17

In normal kidneys, which of the following is true of the osmolarity of renal tubular fluid that flows through the early distal tubule in the region of the macula densa?

Usually hypotonic compared with plasma

As water flows up the ascending limb of the loop of Henle, solutes are reabsorbed, but this segment is relatively impermeable to water; progressive dilution of the tubular fluid occurs so that the osmolarity decreases to approximately 100 mOsm/L by the time the fluid reaches the early distal tubule. Even during maximal antidiuresis, this portion of the renal tubule is relatively impermeable to water and is therefore called the diluting segment of the renal tubule.