Renal Basic Science Qs

Question 1

Autoregulation of GFR

When mean arterial pressure falls from 110 mmHg to 80 mmHg, GFR remains relatively constant.
Which mechanism is primarily responsible?

A. Sympathetic nervous system activation
B. Myogenic response in the afferent arteriole
C. RAAS-mediated efferent vasoconstriction
D. Release of ADH
E. Increased peritubular capillary oncotic pressure

Answer 1

Correct answer: B — Myogenic response

Explanation:
Autoregulation between 80–180 mmHg is intrinsic to the kidney.
The myogenic mechanism detects reduced stretch → afferent dilation → maintains flow + GFR.

Question 2

Tubuloglomerular feedback (TGF)

An increase in NaCl reaching the macula densa causes which change?

A. Increased renin release
B. Afferent arteriole dilation
C. Afferent arteriole constriction
D. Increased GFR
E. Increased aldosterone secretion

Answer 2

Correct answer: C — Afferent arteriole constriction

Explanation:
High NaCl in distal tubule → macula densa senses ↑ flow → releases adenosine → afferent constriction → ↓ GFR.

Question 3

What increases GFR?

Which change would increase GFR?

A. Increased plasma protein concentration
B. Afferent arteriole constriction
C. Efferent arteriole dilation
D. Efferent arteriole constriction
E. Contraction of mesangial cells

Answer 3

Correct answer: D — Efferent arteriole constriction

Explanation:
Moderate efferent constriction ↑ glomerular hydrostatic pressure → ↑ GFR.
(Severe constriction eventually ↓ renal blood flow → ↓ GFR.)

Question 4

Proximal tubule osmolality

The fluid in the proximal tubule remains isosmotic with plasma because:

A. Na⁺ is reabsorbed but water cannot follow
B. Water is reabsorbed without solute
C. Solute and water are reabsorbed in equal proportion
D. ADH controls water reabsorption here
E. Osmotically inactive solutes accumulate

Answer 4

Correct answer: C — Solute and water reabsorbed proportionally

Explanation:
PCT is highly water-permeable → water follows Na⁺ immediately → isosmotic reabsorption → no change in tubular osmolality.

Question 5

Thick ascending limb

A patient takes a loop diuretic. Which nephron process does the drug block?

A. Na⁺/glucose cotransport
B. Na⁺/Cl⁻ cotransport
C. Na⁺/K⁺/2Cl⁻ transporter
D. Na⁺/H⁺ antiporter
E. Aquaporin insertion

Answer 5

Correct answer: C — NKCC2 in thick ascending limb

Explanation:
Loop diuretics block NKCC2 → abolish medullary gradient → massive diuresis.

Question 6

Potassium handling

Which situation increases K⁺ secretion in the distal nephron?

A. Metabolic acidosis
B. Low aldosterone
C. High tubular flow rate
D. Beta-blocker therapy
E. ACE inhibitor therapy

Answer 6

Correct answer: C — High tubular flow rate

Explanation:
High flow “washes away” secreted K⁺ → maintains gradient → ↑ further secretion.
(Other factors that increase secretion: aldosterone, alkalosis, insulin.)

Question 7

Glucose reabsorption

A diabetic patient has a plasma glucose of 16 mmol/L.
His urine contains glucose. Why?

A. Glucose is not filtered
B. Glucose transporters are saturated
C. Glucose is secreted into the tubule
D. Glucose blocks SGLT2
E. Glucose cannot be reabsorbed in PCT

Answer 7

Correct answer: B — Transport maximum (Tm) exceeded

Explanation:
PCT reabsorbs glucose via SGLT2 until transporters saturate → glycosuria occurs once threshold exceeded.

Question 8

Renal plasma flow (RPF) measurement

Which substance is used to estimate effective RPF because it is almost completely cleared in one pass?

A. Inulin
B. Creatinine
C. PAH (para-aminohippurate)
D. Urea
E. Glucose

Answer 8

Correct answer: C — PAH

Explanation:
PAH is filtered + fully secreted → almost 100% cleared → used to estimate RPF.

Question 9

Peritubular capillary reabsorption

Reabsorption from the proximal tubule into peritubular capillaries increases when:

A. Peritubular hydrostatic pressure increases
B. Plasma protein concentration decreases
C. Efferent arteriolar constriction increases
D. Blood flow in vasa recta increases
E. GFR decreases

Answer 9

Correct answer: C — Efferent arteriole constriction

Explanation:
Efferent constriction → ↑ glomerular filtration fraction → ↑ plasma protein concentration in peritubular capillaries → ↑ oncotic pressure → increased reabsorption.