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🎯 HIGH-YIELD MCQ BANK — BATTERJEE MEDICAL COLLEGE

Renal Physiology: Plasma Clearance + Sodium Handling by Renal Tubules

Source: Dr. Hader I. Sakr | Guyton & Hall 13th Ed. | Ganong's 25th Ed.

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Legend:

• ⭐⭐⭐ = Extremely high yield (appeared multiple times in BMC exams)
• ⭐⭐ = High yield (regularly appears)
• ⭐ = Medium yield (occasionally appears)
• ✅ = Correct answer
• 📅 = Reported in BMC past exam papers (based on topic frequency analysis from these lecture slides)

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📘 PART 1: PLASMA CLEARANCE (Slides 5–37)

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MCQ 1 ⭐⭐⭐ | SLIDE 6 | Definition of Plasma Clearance

• A) The total amount of the substance filtered per minute
• B) The concentration of the substance in the urine
• C) The volume of plasma completely cleared of a substance per minute ✅
• D) The rate at which the kidneys produce urine
• E) The amount of substance secreted by the tubules per minute

• A - Wrong: Filtered amount = GFR × plasma concentration. That is NOT clearance.
• B - Wrong: Urine concentration is just how much is in the urine. It is not clearance.
• C - CORRECT: Clearance tells you: "How many milliliters of plasma did the kidneys completely clean per minute?" Formula: Cx = (Ux × V) / Px. If Cx = 125 mL/min, it means 125 mL of plasma is "cleared" every minute.
• D - Wrong: Urine production rate (V) is only one part of the clearance formula, not the definition.
• E - Wrong: Secretion increases excretion but is not the definition of clearance.

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MCQ 2 ⭐⭐⭐ | SLIDE 8 | Clearance Formula (Calculation)

• A) 50 mL/min
• B) 100 mL/min
• C) 200 mL/min ✅
• D) 150 mL/min
• E) 400 mL/min

• Cx = (100 × 2) / 1 = 200 mL/min
• A - Wrong: 50 = 100/2. You divided U by V instead of multiplying.
• B - Wrong: 100 = U alone. You forgot to multiply by V.
• C - CORRECT: (100 × 2) / 1 = 200.
• D - Wrong: No calculation gives 150 here.
• E - Wrong: 400 would come from (100 × 2) × 2, which is wrong.

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MCQ 3 ⭐⭐⭐ | SLIDE 10 | Tubular Handling & Clearance Values

• A) Glucose
• B) Urea
• C) Inulin ✅
• D) Creatinine
• E) Para-aminohippuric acid (PAH)

• A - Wrong: Glucose is completely reabsorbed, so its clearance = 0. None appears in urine normally.
• B - Wrong: Urea is partially reabsorbed, so its clearance is between 0 and 125 mL/min.
• C - CORRECT: Inulin is the gold standard for GFR because it is freely filtered and neither reabsorbed nor secreted.
• D - Wrong: Creatinine is partially secreted, so its clearance is slightly MORE than 125 mL/min.
• E - Wrong: PAH clearance (~625 mL/min) equals renal plasma flow, not GFR.

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MCQ 4 ⭐⭐⭐ | SLIDE 11–12 | Inulin as Gold Standard for GFR

• A) It is produced endogenously by muscle metabolism
• B) It is freely filtered AND neither reabsorbed nor secreted by tubules ✅
• C) It is completely secreted by the proximal convoluted tubule
• D) It is bound to plasma proteins and therefore not filtered
• E) It stimulates tubular reabsorption of glucose

• A - Wrong: Inulin is NOT endogenous. It is extracted from Jerusalem artichokes and must be infused IV. Creatinine is the endogenous marker.
• B - CORRECT: The perfect GFR marker must: (1) be freely filtered, (2) NOT be reabsorbed, (3) NOT be secreted, (4) NOT be metabolized, (5) NOT affect kidney function. Inulin meets ALL of these.
• C - Wrong: That describes PAH, not inulin. If inulin was secreted, its clearance would be HIGHER than GFR.
• D - Wrong: Protein-bound substances are NOT freely filtered - they cannot cross the glomerular membrane. Inulin is not protein-bound.
• E - Wrong: Inulin has no pharmacological effect on any transporter.

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MCQ 5 ⭐⭐⭐ | SLIDE 12 | GFR Calculation (Numerical)

• A) 60 mL/min
• B) 90 mL/min
• C) 120 mL/min ✅
• D) 240 mL/min
• E) 180 mL/min

1. Urine flow (V) = 120 mL / 2 hours = 60 mL/hr = 1 mL/min
2. GFR = (Ux × V) / Px = (240 × 1) / 2 = 120 mL/min

• A - Wrong: 60 is the urine volume in mL/hr before converting to mL/min.
• B - Wrong: No calculation gives 90 here.
• C - CORRECT: (240 × 1) / 2 = 120 mL/min. This is within normal range (100-125 mL/min).
• D - Wrong: 240 is just the urine inulin concentration (Ux), not the GFR.
• E - Wrong: 180 would arise from forgetting to convert urine volume to mL/min.

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MCQ 6 ⭐⭐⭐ | SLIDE 13 | Creatinine Clearance vs Inulin

• A) Creatinine is completely reabsorbed by the tubule
• B) Creatinine is freely filtered and not secreted
• C) Tubular secretion overestimates creatinine, but non-specific chromogens overestimate plasma creatinine, so errors cancel out ✅
• D) Creatinine is never measured in plasma
• E) Creatinine clearance is always exactly equal to inulin clearance

• A - Wrong: Creatinine is NOT reabsorbed. It is partially SECRETED by the PCT.
• B - Wrong: Creatinine IS secreted by the proximal tubule, which makes its clearance slightly HIGHER than true GFR.
• C - CORRECT: Two errors cancel each other: (1) Tubular secretion adds creatinine to urine, making U×V artificially HIGH. (2) Colorimetric tests also measure non-specific chromogens in plasma, making Pcr artificially HIGH. These two overestimates cancel each other out, making creatinine clearance ≈ inulin clearance.
• D - Wrong: Plasma creatinine is routinely measured in all renal function tests.
• E - Wrong: They are close but not identical; creatinine clearance slightly overestimates GFR at low creatinine levels.

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MCQ 7 ⭐⭐⭐ | SLIDE 14–15 | PAH Clearance = Renal Plasma Flow

• A) It is completely filtered and completely reabsorbed in one circulation
• B) It is freely filtered and completely secreted from peritubular blood in one circulation ✅
• C) It is produced endogenously in large amounts
• D) It is bound to plasma proteins and not filtered
• E) It measures GFR more accurately than inulin

• A - Wrong: PAH is secreted, not reabsorbed. If it were reabsorbed, its clearance would be LESS than GFR.
• B - CORRECT: PAH is (1) freely filtered at the glomerulus AND (2) any PAH that wasn't filtered gets secreted from peritubular capillaries into tubule. So essentially ALL the PAH in arterial blood ends up in the urine. Clearance of PAH ≈ total renal plasma flow.
• C - Wrong: PAH is an exogenous substance that must be infused.
• D - Wrong: Protein-bound substances are not freely filtered.
• E - Wrong: PAH does NOT measure GFR. It measures RPF. GFR is measured by inulin.

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MCQ 8 ⭐⭐⭐ | SLIDE 16 | PAH Numerical Calculation

• A) 630 mL/min
• B) 700 mL/min
• C) 1273 mL/min ✅
• D) 945 mL/min
• E) 1400 mL/min

1. ERPF = (14 × 0.9) / 0.02 = 12.6 / 0.02 = 630 mL/min
2. Actual RPF = 630 / 0.9 = 700 mL/min
3. RBF = RPF / (1 - Hematocrit) = 700 / (1 - 0.45) = 700 / 0.55 = 1273 mL/min

• A - Wrong: 630 is the ERPF, not RBF.
• B - Wrong: 700 is the actual RPF, not RBF.
• C - CORRECT: RBF = RPF / (1 - HV) = 700 / 0.55 ≈ 1273 mL/min. Normal RBF ≈ 1200-1250 mL/min.
• D - Wrong: 945 doesn't come from any step in this calculation.
• E - Wrong: 1400 would come from using HV = 0.5 instead of 0.45.

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MCQ 9 ⭐⭐⭐ | SLIDE 17 | Filtration Fraction

• A) 0.25; normal range 0.25-0.35
• B) 0.19; normal range 0.16-0.20 ✅
• C) 0.10; normal range 0.10-0.15
• D) 0.35; normal range 0.30-0.40
• E) 0.50; normal range 0.45-0.55

• A - Wrong: 0.25 is too high; normal FF is about 0.2 (20%).
• B - CORRECT: About 20% of plasma entering the glomerulus gets filtered. The remaining 80% exits through the efferent arteriole to form peritubular capillaries.
• C - Wrong: 0.10 is too low.
• D/E - Wrong: These are far outside normal range.

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MCQ 10 ⭐⭐ | SLIDE 19–20 | Tubular Reabsorption vs Secretion

• A) From the tubular lumen into the peritubular capillaries
• B) From the glomerulus into Bowman's space
• C) From the peritubular capillary blood into the renal tubule ✅
• D) From the interstitium into the tubular cells only
• E) From the tubule into the renal pelvis

• A - Wrong: That is REABSORPTION (tubule → capillary).
• B - Wrong: That is FILTRATION (capillary → Bowman's space).
• C - CORRECT: Secretion = blood → tubule. The substance moves from peritubular capillaries, across the tubular cell or tight junctions, INTO the tubular lumen to be excreted.
• D - Wrong: This is only half the process. Secretion must also include transport from the cell into the tubular lumen.
• E - Wrong: Movement into the renal pelvis is just drainage, not secretion.

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MCQ 11 ⭐⭐⭐ | SLIDE 21 | Primary Active Transport - Na+/K+ ATPase

• A) Pumps 2 Na+ out and 3 K+ into the cell, creating a positive intracellular charge
• B) Pumps 3 Na+ out and 2 K+ into the cell, creating a negative intracellular charge of about -70 mV ✅
• C) Pumps Na+ into the cell along with glucose via SGLT-2
• D) Uses passive diffusion and does not require ATP
• E) Is located at the luminal (apical) membrane of tubular cells

• A - Wrong: The numbers are reversed! It's 3 Na+ OUT, 2 K+ IN. Also, the net charge is NEGATIVE inside the cell (more cations pumped out than brought in).
• B - CORRECT: The pump moves 3 Na+ out of the cell in exchange for 2 K+ brought in. Since more positive charge leaves than enters, the inside becomes negative (~-70 mV). This also keeps intracellular Na+ low, creating a favorable gradient for Na+ to diffuse FROM the lumen INTO the cell.
• C - Wrong: That describes secondary active transport (SGLT-2 co-transport) at the luminal membrane. Na+/K+ ATPase is at the basolateral membrane.
• D - Wrong: This pump uses ATP directly (primary active transport). It has ATPase activity.
• E - Wrong: Na+/K+ ATPase is at the BASOLATERAL membrane (blood side), not the luminal (urine side) membrane.

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MCQ 12 ⭐⭐⭐ | SLIDE 22–23 | Secondary Active Transport - SGLT-2

• A) Primary active transport using Na+/K+ ATPase at the luminal membrane
• B) Facilitated diffusion via GLUT-2 at the luminal membrane
• C) Secondary active transport (symport) via SGLT-2 at the luminal membrane ✅
• D) Paracellular diffusion through tight junctions
• E) Pinocytosis like protein reabsorption

• A - Wrong: Na+/K+ ATPase is at the BASOLATERAL membrane, not luminal. Also, glucose uses SECONDARY active transport, not primary.
• B - Wrong: GLUT-2 is at the BASOLATERAL membrane (to exit the cell into interstitium). SGLT-2 is the luminal transporter.
• C - CORRECT: At the LUMINAL membrane: Na+ and glucose BOTH bind to SGLT-2. As Na+ flows DOWN its gradient (from tubule into cell), glucose is pulled WITH it AGAINST its gradient (secondary active transport / co-transport / symport). Energy comes indirectly from the Na+ gradient created by Na+/K+ ATPase.
• D - Wrong: Glucose is too large and polar for paracellular diffusion.
• E - Wrong: Pinocytosis is for PROTEINS, not glucose.

1. Luminal: Na+ + Glucose → SGLT-2 → enters cell together
2. Basolateral: Glucose → GLUT-2 → exits into interstitium (facilitated diffusion)
3. Basolateral: Na+ → Na+/K+ ATPase → pumped out (the energy source for step 1)

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MCQ 13 ⭐⭐ | SLIDE 24 | Antiport / Counter-Transport

• A) Both Na+ and H+ entering the tubular cell together
• B) Na+ entering the cell as H+ is pumped OUT into the tubular lumen ✅
• C) Both Na+ and H+ leaving the cell
• D) H+ entering the cell as Na+ is pumped out
• E) Na+ and HCO3- both being secreted into the lumen

• A - Wrong: In co-transport (symport), both substances move in the same direction. Antiport means OPPOSITE directions.
• B - CORRECT: As Na+ moves into the cell (down its gradient - favorable), H+ is forced OUT into the tubular lumen (against H+'s gradient - requires energy). This is "counter-transport" because they move in opposite directions. The energy driving H+ secretion comes from Na+ diffusion.
• C - Wrong: Na+ comes INTO the cell in this process.
• D - Wrong: This reverses the directions of both ions.
• E - Wrong: HCO3- is reabsorbed (not secreted) via H+ secretion - the H+ combines with filtered HCO3- to form CO2 + H2O, which diffuses in and regenerates HCO3-.

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MCQ 14 ⭐⭐ | SLIDE 25–26 | Passive Reabsorption

• A) It is co-transported with K+ via NKCC2
• B) It binds to SGLT-2 along with Na+
• C) Active reabsorption of Na+ leaves the lumen electrically negative, attracting Cl- ✅
• D) It follows osmotic movement of water
• E) It is reabsorbed by primary active transport via Cl-/HCO3- ATPase

• A - Wrong: NKCC2 co-transport is in the THICK ASCENDING LIMB of the loop of Henle, not the PCT.
• B - Wrong: SGLT-2 transports Na+ and glucose, not Cl-.
• C - CORRECT: When positively charged Na+ is actively pumped OUT of the tubular lumen, the lumen becomes negatively charged. This negative charge ATTRACTS negatively charged Cl- which then diffuses OUT passively via the paracellular route (through tight junctions).
• D - Wrong: Water follows osmotic gradients, but Cl- movement is primarily driven by electrical gradient (the negative lumen), not osmosis.
• E - Wrong: There is no Cl-/HCO3- ATPase. Chloride reabsorption in PCT is passive.

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MCQ 15 ⭐⭐ | SLIDE 27 | Pinocytosis

• A) SGLT-2 co-transport
• B) Na+/H+ antiport
• C) Facilitated diffusion via GLUT transporters
• D) Pinocytosis followed by lysosomal digestion to amino acids ✅
• E) Passive diffusion through tight junctions

• A, B, C - Wrong: These are all specific to small molecules like glucose, H+, or Na+. Proteins are too large for carrier-mediated transport.
• D - CORRECT: Proteins bind to the luminal membrane → the membrane invaginates (folds inward) → a vesicle forms around the protein → lysosomal enzymes digest the protein into amino acids → amino acids are transported across the basolateral membrane into the interstitium.
• E - Wrong: Proteins are too large to passively diffuse through tight junctions.

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MCQ 16 ⭐⭐⭐ | SLIDE 29–30 | Tubular Transport Maximum (Tm) & Glucose

• A) 180 mg/dL ✅ (approximately)
• B) 350-375 mg/dL (where Tm is reached)
• C) 70 mg/dL (normal fasting blood glucose)
• D) 500 mg/dL
• E) 100 mg/dL

• A - CORRECT: At plasma glucose ~180 mg/dL, SGLT-2 transporters begin to be saturated. Some glucose "escapes" into the urine. This is the THRESHOLD. Note: Some nephrons reach saturation before others due to variation - this is called "splay."
• B - Wrong: 350-375 mg/dL is the Tm (tubular transport maximum), where ALL transporters are saturated and reabsorption is maximal. This is different from threshold.
• C - Wrong: 70-100 mg/dL is normal fasting blood glucose. At this level, ALL filtered glucose is reabsorbed (no glucosuria).
• D - Wrong: Way above both threshold and Tm.
• E - Wrong: 100 mg/dL is still within normal range; no glucosuria at this level.

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MCQ 17 ⭐⭐ | SLIDE 30 | Substances Showing Tm

• A) Glucose
• B) Amino acids
• C) Phosphate
• D) PAH (Para-aminohippuric acid) ✅
• E) Water

• A, B, C - Wrong: These have Tm for REABSORPTION (they are reabsorbed up to a maximum rate).
• D - CORRECT: PAH is actively SECRETED by peritubular capillaries into the tubular lumen with a high affinity. At low plasma PAH concentrations, essentially ALL PAH in peritubular blood is secreted. Above a certain concentration, the secretory transporters become saturated - this is the Tm for secretion.
• E - Wrong: Water reabsorption is regulated by ADH/AQP channels and follows osmotic gradients. It does not have a Tm in the same sense.

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MCQ 18 ⭐⭐⭐ | SLIDE 32 | Gradient-Time Transport

• A) Na+ has no carrier proteins in the PCT
• B) The rate of Na+ transport at the basolateral border exceeds the rate at the brush border ✅
• C) Na+ is completely reabsorbed before reaching the loop of Henle
• D) Na+ requires aldosterone in the PCT
• E) The PCT is impermeable to Na+

• A - Wrong: Na+ DOES have carrier proteins (SGLT-2, Na+/H+ exchanger, NKCC2 in TAL etc.). The issue is about the RATE of different steps.
• B - CORRECT: In gradient-time transport, the rate of reabsorption depends on (1) the concentration gradient and (2) how long the fluid stays in contact with the tubule. In PCT: Na+ enters the cell through luminal channels/transporters SLOWLY, but Na+/K+ ATPase at the basolateral side pumps it out FASTER. So the LIMITING STEP is the entry from the lumen side. The gradient (concentration of Na+ in lumen) and time (tubular flow rate) determine how much gets reabsorbed - hence "gradient-time."
• C - Wrong: Only 60-65% of Na+ is reabsorbed in PCT. The rest continues.
• D - Wrong: Aldosterone acts on LATE DCT and collecting ducts, not PCT.
• E - Wrong: PCT is highly permeable to Na+.

1. [Na+] in PCT: higher concentration → faster reabsorption
2. Flow rate: SLOWER flow → MORE Na+ reabsorbed (more time in contact)

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MCQ 19 ⭐⭐ | SLIDE 34 | Peritubular Capillary Forces

• A) 28 mmHg
• B) 38 mmHg
• C) 10 mmHg ✅
• D) 6 mmHg
• E) 15 mmHg

• Forces FAVORING reabsorption: Oncotic pressure of peritubular capillaries (32) + Interstitial HP (6) = 38 mmHg
• Forces OPPOSING reabsorption: Peritubular capillary HP (13) + Interstitial oncotic pressure (15) = 28 mmHg
• Net = 38 - 28 = 10 mmHg (favors reabsorption)

• A - Wrong: 28 mmHg is the total opposing forces, not the net.
• B - Wrong: 38 mmHg is the total favoring forces, not the net.
• C - CORRECT: Net = Favoring - Opposing = 38 - 28 = 10 mmHg. This small positive force drives fluid from the interstitium into the peritubular capillaries.
• D - Wrong: 6 mmHg is just the interstitial hydrostatic pressure value.
• E - Wrong: 15 mmHg is the interstitial oncotic pressure value.

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📗 PART 2: SODIUM HANDLING BY RENAL TUBULES (Slides 5–28)

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MCQ 20 ⭐⭐⭐ | SLIDE 5 | Importance of Sodium / % Reabsorbed

• A) 50-60%; uses 50% of kidney's energy
• B) 75-80%; uses 75% of kidney's energy
• C) 96-99%; uses 90% of kidney's energy ✅
• D) 100%; uses 100% of kidney's energy
• E) 85-90%; uses 60% of kidney's energy

• A, B, E - Wrong: These percentages are too low. The kidney must reabsorb almost ALL filtered Na+ or severe dehydration and electrolyte imbalance would occur rapidly.
• C - CORRECT: 96-99% of filtered Na+ is reabsorbed. This process requires 90% of kidney's oxygen consumption. Na+ reabsorption "drives" reabsorption of almost everything else (glucose, amino acids, water, Cl-) via secondary active mechanisms.
• D - Wrong: About 1-4% of Na+ IS excreted in urine (= regulatory zone). Complete reabsorption would mean zero urinary Na+ excretion, which never occurs.

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MCQ 21 ⭐⭐⭐ | SLIDE 8 | Na+ Reabsorption in PCT (60-65%)

• A) 25%
• B) 7%
• C) 3%
• D) 60-65% ✅
• E) 50%

• A - Wrong: 25% is the TAL/loop of Henle.
• B - Wrong: 7% is the early DCT (via NCC).
• C - Wrong: 3% is the late DCT/collecting duct (aldosterone-regulated).
• D - CORRECT: PCT reabsorbs the majority. This makes sense - PCT needs to handle the bulk load efficiently.
• E - Wrong: 50% is not a recognized value for any segment.

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MCQ 22 ⭐⭐⭐ | SLIDE 8 | First Half of PCT - Cotransported Solutes

• A) Glucose
• B) Amino acids
• C) HCO3-
• D) Chloride ✅
• E) Phosphate

• In the FIRST HALF of PCT: Na+ is co-transported with glucose, amino acids, sulphate, phosphate, organic acids (lactate, citrate), and HCO3-. This is also where ALL filtered glucose and amino acids are reabsorbed.
• D - CORRECT (the exception): Cl- is the anion that accompanies Na+ in the SECOND (LATE) half of PCT, not the first half. In the first half, the focus is on glucose, amino acids, and bicarbonate. In the second half, the primary process is NaCl reabsorption.
• A, B, C, E - Wrong: These ARE co-transported with Na+ in the first half of PCT.

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MCQ 23 ⭐⭐⭐ | SLIDE 11 | Thin Descending Limb of Loop of Henle

• A) Reabsorbs Na+ but is impermeable to water
• B) Reabsorbs both Na+ and water equally
• C) Is impermeable to water but reabsorbs Na+ via NKCC2
• D) Reabsorbs water but has NO Na+ transport proteins/channels ✅
• E) Secretes Na+ into the lumen

• A - Wrong: That describes the THICK ASCENDING LIMB - reabsorbs ions but NOT water.
• B - Wrong: No segment reabsorbs both water and Na+ equally in the loop.
• C - Wrong: NKCC2 is in the THICK ascending limb, not the thin descending limb.
• D - CORRECT: The thin DESCENDING limb is highly permeable to WATER but has NO Na+ transport proteins in the luminal membrane. Water is reabsorbed osmotically as the tubular fluid enters the hypertonic medullary interstitium. As water leaves, Na+ concentration in the lumen INCREASES (reaching ~1200-1400 mOsm/L at the bend).
• E - Wrong: Na+ is not secreted into any segment of the tubule.

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MCQ 24 ⭐⭐⭐ | SLIDE 12 | NKCC2 in Thick Ascending Limb

• A) 1 Na+ : 1 K+ : 1 Cl-
• B) 2 Na+ : 1 K+ : 2 Cl-
• C) 1 Na+ : 1 K+ : 2 Cl- ✅
• D) 1 Na+ : 2 K+ : 1 Cl-
• E) 1 Na+ : 1 Cl- (NCC)

• C - CORRECT: NKCC2 co-transports 1 Na+ : 1 K+ : 2 Cl- from the tubular lumen into the cell. This is driven by the low intracellular Na+ maintained by basolateral Na+/K+ ATPase.
• E - Wrong: NCC (Na+/Cl- co-transporter carrying 1:1) is in the EARLY DCT, not the TAL.
• The other ratios (A, B, D) are incorrect.

• Reabsorbs 25% of filtered Na+, K+, and Cl-
• Impermeable to WATER → tubular fluid becomes DILUTE (100 mOsm/L)
• Called "diluting segment"
• Most K+ that enters the cell leaks BACK into the lumen → creates net positive lumen potential → drives paracellular reabsorption of Ca2+, Mg2+, Na+, K+

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MCQ 25 ⭐⭐⭐ | SLIDE 13 | Bartter's Syndrome

• A) Conn's syndrome (primary hyperaldosteronism)
• B) Liddle's syndrome (gain of function ENaC mutation)
• C) Gitelman syndrome (NCC defect in DCT)
• D) Bartter's syndrome (NKCC2 defect in TAL) ✅
• E) Pseudohypoaldosteronism

• A - Wrong: Conn's syndrome causes HYPERTENSION and LOW renin due to aldosterone excess from adenoma.
• B - Wrong: Liddle's syndrome causes HYPERTENSION, hypokalemia, metabolic alkalosis, and LOW aldosterone/renin (gain-of-function ENaC mutation).
• C - Wrong: Gitelman syndrome also causes salt wasting and metabolic alkalosis but features HYPOCALCIURIA (low urine Ca2+) and hypomagnesemia. Bartter's has HYPERcalciuria.
• D - CORRECT: Bartter's syndrome = defect in NKCC2 (like taking furosemide forever). Results in:
  • Salt (Na+, K+, Cl-) wasting → volume depletion → activates renin-angiotensin-aldosterone
  • Loss of Ca2+ (hypercalciuria) - because the NKCC2 failure also loses the lumen-positive potential that drives paracellular Ca2+ reabsorption
  • Metabolic alkalosis - because compensatory increased Na+ reabsorption in DCT exchanges for H+ secretion
  • Low BP despite high renin/aldosterone
• E - Wrong: Pseudohypoaldosteronism is end-organ resistance to aldosterone - presents with high K+ (hyperkalemia).

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MCQ 26 ⭐⭐⭐ | SLIDE 14 | Early DCT - NCC Transporter

• A) NKCC2 co-transporter (Na+/K+/2Cl-)
• B) ENaC (epithelial sodium channels)
• C) NCC (Na+/Cl- co-transporter) ✅
• D) Na+/H+ antiporter
• E) Na+/K+ ATPase at the luminal membrane

• A - Wrong: NKCC2 is in the THICK ASCENDING LIMB. Target of LOOP diuretics.
• B - Wrong: ENaC is in the LATE DCT and COLLECTING DUCT. Target of aldosterone and K+-sparing diuretics.
• C - CORRECT: The early DCT uses NCC (Na+/Cl- co-transporter) to reabsorb 7% of filtered Na+. This segment is also impermeable to water → further dilutes the tubular fluid to ~60 mOsm/L ("cortical diluting segment").
• D - Wrong: Na+/H+ antiporter is predominantly in the PCT (helps bicarbonate reabsorption).
• E - Wrong: Na+/K+ ATPase is ALWAYS at the basolateral membrane as the driving force. It is never at the luminal membrane.

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MCQ 27 ⭐⭐⭐ | SLIDE 16 | Late DCT & CDs - ENaC and Aldosterone

• A) NKCC2, which is stimulated by ANP
• B) NCC, which is inhibited by thiazides
• C) ENaC channels, stimulated by aldosterone, in exchange for K+ secretion ✅
• D) SGLT-2, stimulated by insulin
• E) Na+/H+ antiport, stimulated by cortisol

• C - CORRECT: Principal (P) cells in the late DCT and collecting ducts have ENaC (Epithelial Na+ Channel) on the apical membrane. Aldosterone acts on these cells to:
  1. Increase the NUMBER of ENaC channels in the apical membrane
  2. Increase basolateral Na+/K+ ATPase molecules
  3. Increase ATP production
  • Result: More Na+ reabsorption IN EXCHANGE for K+ secretion (K+ enters via basolateral Na+/K+ ATPase and exits via apical K+ channels)
• A - Wrong: NKCC2 is in the TAL; ANP INHIBITS Na+ reabsorption in the CDs.
• B - Wrong: NCC is in early DCT; thiazides block it.
• D - Wrong: SGLT-2 is in the PCT; insulin does not directly regulate ENaC.
• E - Wrong: Na+/H+ antiport is in PCT, not late DCT/CDs.

• Spironolactone/Eplerenone: Aldosterone ANTAGONISTS → block ENaC → Na+ excretion + K+ RETENTION (K+-sparing diuretics). Used in heart failure, Conn's syndrome, ascites.
• Amiloride/Triamterene: Directly BLOCK ENaC → same K+-sparing effect but without blocking aldosterone receptor.
• Liddle's syndrome: Gain-of-function ENaC mutation → HTN + hypokalemia + metabolic alkalosis (responds to amiloride, NOT spironolactone).

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MCQ 28 ⭐⭐⭐ | SLIDE 19 | Glomerulo-Tubular Balance

• A) An increase in GFR causes a proportional decrease in Na+ reabsorption
• B) Na+ reabsorption is fixed at exactly 125 mEq/min regardless of GFR
• C) The renal tubules always reabsorb a constant PERCENTAGE (2/3 = 65%) of filtered Na+ and water ✅
• D) GFR and RPF always increase proportionally together
• E) Aldosterone maintains constant Na+ excretion

• A - Wrong: The opposite is true. Increased GFR → increased reabsorption (not decreased).
• B - Wrong: It's a constant PERCENTAGE (65%), not a constant AMOUNT. If GFR doubles, reabsorption doubles. If GFR halves, reabsorption halves.
• C - CORRECT: Glomerulo-tubular balance = the PCT reabsorbs a constant fraction (~65%) of whatever is filtered, regardless of GFR. This is HORMONE-INDEPENDENT and occurs even in an isolated kidney. It prevents the distal tubule from being overwhelmed when GFR suddenly rises.
• D - Wrong: GFR and RPF can change independently.
• E - Wrong: Aldosterone is important for fine-tuning in the late DCT/CDs but has nothing to do with glomerulo-tubular balance in the PCT.

1. Prevents overloading the distal tubule when GFR rises
2. Prevents inappropriate Na+ and water loss if GFR suddenly increases

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MCQ 29 ⭐⭐⭐ | SLIDE 22–23 | Angiotensin II as Na+ Retainer

• A) Aldosterone - acts directly on PCT, TAL, and DCT
• B) ADH (vasopressin) - acts by increasing water channels in collecting duct
• C) Angiotensin II - acts via aldosterone stimulation, direct PCT effects, and efferent arteriolar constriction ✅
• D) ANP - acts via cGMP to increase Na+ reabsorption
• E) Cortisol - acts via nuclear receptors to increase ENaC

• A - Wrong: Aldosterone acts on LATE DCT/CDs via ENaC. It is powerful but is actually controlled BY angiotensin II.
• B - Wrong: ADH acts on water channels (AQP2) in collecting duct - it retains WATER, not specifically Na+.
• C - CORRECT: Angiotensin II retains Na+ through MULTIPLE mechanisms:
  1. Stimulates aldosterone secretion → ENaC activation in late DCT/CDs
  2. Direct action on PCT cells: Stimulates Na+/K+ ATPase pump AND Na+/H+ counter-transport
  3. Constricts efferent arterioles (EA): Reduces peritubular capillary HP and increases their oncotic pressure → more interstitial fluid reabsorption → more Na+ and water retained
  4. Net effect: GREATEST sodium retention of any single hormone
• D - Wrong: ANP DECREASES Na+ reabsorption (acts opposite way - increases natriuresis).
• E - Wrong: Cortisol has WEAK mineralocorticoid activity. It is not the primary Na+-retaining hormone.

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MCQ 30 ⭐⭐⭐ | SLIDE 24 | ANP - Mechanism & Effects

• A) Relaxing mesangial cells → increases glomerular surface area → increases GFR
• B) Vasodilation of the afferent arteriole → increases GFR
• C) Inhibiting apical ENaC channels in late DCT/CDs
• D) Inhibiting renin secretion → decreasing angiotensin II and aldosterone
• E) Stimulating Na+/K+ ATPase in basolateral membrane of collecting duct ✅

• A - Correct mechanism: Relaxes mesangial cells → increases filtration surface area → ↑ GFR → more Na+ filtered → more excreted
• B - Correct mechanism: Afferent arteriole vasodilation → more blood enters glomerulus → ↑ GFR
• C - Correct mechanism: Directly INHIBITS ENaC channels in P cells → less Na+ reabsorbed
• D - Correct mechanism: Inhibits renin → less angiotensin II → less aldosterone → less ENaC stimulation
• E - WRONG/EXCEPTION: ANP INHIBITS Na+/K+ ATPase in the basolateral membrane, it does NOT stimulate it. Stimulating Na+/K+ ATPase would INCREASE Na+ reabsorption, which is the OPPOSITE of ANP's effect.

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MCQ 31 ⭐⭐⭐ | SLIDE 27–28 | Diuretics and Their Sites of Action

• A) Inhibiting Na+/H+ antiport in PCT
• B) Blocking aldosterone receptors in late DCT
• C) Inhibiting Na+/Cl- co-transporter (NCC) in early DCT
• D) Inhibiting NKCC2 co-transporter in the thick ascending limb ✅
• E) Blocking ENaC channels in collecting duct

• A - Wrong: Acetazolamide effects are in PCT by blocking carbonic anhydrase.
• B - Wrong: That's spironolactone (in late DCT/CDs).
• C - Wrong: That's hydrochlorothiazide (thiazides).
• D - CORRECT: Furosemide (and bumetanide, torsemide) block NKCC2, preventing 25% of filtered Na+ from being reabsorbed → powerful diuresis.
• E - Wrong: That's amiloride or triamterene.

• Furosemide: Used in acute pulmonary edema (fastest-acting diuretic), heart failure, hypertensive emergency. Causes hypokalemia, hyponatremia, hypocalcemia, ototoxicity.
• Thiazides: First-line for essential hypertension. Cause hypokalemia but HYPOcalciuria (good for kidney stones).
• Spironolactone: Used in heart failure (RALES trial - reduces mortality), Conn's syndrome, cirrhosis with ascites. K+-sparing.

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MCQ 32 ⭐⭐ | SLIDE 20–21 | Pressure Natriuresis

• A) Increased aldosterone secretion when BP rises
• B) Increased peritubular capillary hydrostatic pressure → increased interstitial HP → back-leak of Na+ into tubular lumen ✅
• C) Direct stimulation of NKCC2 by high BP
• D) Decreased renin secretion as the only mechanism
• E) Increased GFR only, with no change in tubular reabsorption

1. Decreased angiotensin II: Less vasoconstriction → less direct PCT Na+ reabsorption
2. Increased peritubular capillary HP: High BP → more pressure in peritubular capillaries → opposing reabsorptive force increases → net: less fluid moves from interstitium into peritubular capillaries → interstitial fluid HP RISES → Na+ "back-leaks" into the tubular lumen → more Na+ in urine

• A - Wrong: Aldosterone DECREASES when BP rises (less angiotensin II → less aldosterone stimulation).
• B - CORRECT: The physical force mechanism (Starling forces) is the primary mechanism, independent of nerves or hormones.
• C - Wrong: High BP does not directly stimulate NKCC2.
• D - Wrong: Decreased renin is ONE mechanism but not the only one. The physical (back-leak) mechanism is independent.
• E - Wrong: Both GFR changes AND tubular reabsorption changes contribute.

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MCQ 33 ⭐⭐ | SLIDE 26 | Sympathetic Stimulation and Na+ Reabsorption

• A) Increasing renin secretion from juxtaglomerular cells
• B) Directly stimulating Na+ reabsorption in PCT and TAL
• C) Increasing filtration fraction by constricting renal vessels
• D) Inhibiting aldosterone secretion ✅
• E) Angiotensin II formation following renin release

• A - Correct mechanism: SNS → renin release from JG cells → angiotensin I → II → aldosterone → more Na+ reabsorption in CDs
• B - Correct mechanism: Direct α1 stimulation of PCT and TAL tubular cells → increased Na+ reabsorption
• C - Correct mechanism: Renal vasoconstriction → ↑ FF → ↑ oncotic pressure in peritubular capillaries → more reabsorption
• E - Correct mechanism: Renin → angiotensin II → direct PCT effect AND aldosterone stimulation
• D - WRONG: Sympathetic stimulation INCREASES aldosterone (via renin-angiotensin-aldosterone cascade). It does NOT inhibit it. Inhibiting aldosterone would cause Na+ wasting, which is the opposite of what the sympathetic system does.

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BONUS MCQ 34 ⭐⭐⭐ | INTEGRATED CONCEPT | Thin Ascending Limb

• A) Reabsorbs water but NOT Na+
• B) Reabsorbs Na+ passively and is IMPERMEABLE to water ✅
• C) Reabsorbs Na+ via NKCC2 actively
• D) Has no function in Na+ reabsorption
• E) Is the main site of Ca2+ reabsorption

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📋 QUICK REFERENCE: BMC EXAM CHEAT SHEET

Clearance Values (Memorize These Numbers)

Na+ Reabsorption by Segment (Memorize %)

High-Yield Formula Summary

• Clearance: Cx = (Ux × V) / Px
• GFR: = Cin = (Uin × V) / Pin = 125 mL/min normal
• ERPF: = CPAH = (UPAH × V) / PPAH = ~625 mL/min
• Actual RPF: = ERPF / 0.9 = ~700 mL/min
• RBF: = RPF / (1 - HV) = ~1200 mL/min
• FF: = GFR / RPF = 125/700 = 0.16-0.20

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• Guyton and Hall Textbook of Medical Physiology, 13th Edition (Unit V, Chapter 26), pp. 331-2, 340-58, 365-8
• Ganong's Review of Medical Physiology, 25th Edition (Section VII, Chapter 37), pp. 674-83
• Medical Physiology (Boron & Boulpaep), Fig. 34-1 - Inulin handling diagram
• Costanzo Physiology, 7th Edition, Fig. 6.15 - Glucose titration curve
• Guyton & Hall, Fig. 28.22 - GFR vs plasma creatinine; Fig. 28.23 - PAH and RPF