Filtration and drug clearance · Renal & GI
Nephron Function MCQ
Glomerular filtration, segmental reabsorption (PCT, loop, DCT, collecting duct), aldosterone/ADH/ANP regulation, and how diuretics map onto nephron sites. 25 MCQs and 8 INBDE patient cases.
25 practice MCQsQuick-reference tableMnemonics + clinical pearlsFull distractor explanations
High-yield review
Concept summary and clinical relevance.
Quick-reference structure first, then detailed coverage. Mnemonics in amber, clinical pearls in blue.
Renal physiology questions on the INBDE focus on which segment of the nephron does what, and how hormones (aldosterone, ADH, ANP) and diuretics act at specific sites. Match the segment to the function and the drug to the segment, and most renal questions become straightforward.
Nephron segments: function & key transport
| Segment | Reabsorbs / handles | Permeability |
|---|---|---|
| Glomerulus / Bowman's capsule | Filters plasma → filtrate (water, ions, glucose, urea pass; proteins/cells stay) | Filtration barrier |
| Proximal tubule (PCT) | ~65% of Na⁺ + water; all glucose, amino acids; bicarbonate; secretes H⁺ and drugs | Water and solute permeable |
| Descending limb of Henle | Water out → filtrate concentrates | Water-permeable; solute-impermeable |
| Thick ascending limb | Na⁺-K⁺-2Cl⁻ pumped out → filtrate dilutes | Solute-permeable; water-impermeable |
| Early DCT | Na⁺/Cl⁻ reabsorption | Water-impermeable |
| Late DCT + collecting duct | Aldosterone-driven Na⁺/K⁺; ADH-driven water reabsorption | Hormonally regulated |
Hormonal regulation
| Hormone | Source | Action |
|---|---|---|
| Aldosterone | Adrenal cortex (zona glomerulosa) | ↑ Na⁺ reabsorption + ↑ K⁺ secretion in late DCT/collecting duct |
| ADH (vasopressin) | Posterior pituitary | Inserts aquaporins in collecting duct → ↑ water reabsorption |
| Renin | Juxtaglomerular cells (JGA) | Initiates RAAS → angiotensin II → aldosterone |
| ANP (atrial natriuretic peptide) | Atrial myocytes | Opposes RAAS → ↑ Na⁺ and water excretion (natriuresis) |
| Angiotensin II | From AT-I via ACE in lungs | Vasoconstriction, aldosterone release, ADH release |
Diuretics: site of action & key side effect
| Class | Site | Side effect to know |
|---|---|---|
| Carbonic anhydrase inhibitors (acetazolamide) | Proximal tubule | Metabolic acidosis |
| Loop diuretics (furosemide) | Thick ascending limb | Hypokalemia, ototoxicity |
| Thiazides (HCTZ) | Early DCT | Hypokalemia, hyponatremia, hypercalcemia |
| Potassium-sparing (spironolactone, amiloride) | Late DCT / collecting duct | Hyperkalemia |
Clinical pearl, Why this matters in dentistry
Renal function determines drug clearance for many dental medications: penicillin, NSAIDs, and some local anesthetics. CKD patients need dose adjustments. Diuretic side effects matter too: thiazide hypokalemia + epinephrine can precipitate arrhythmias; spironolactone hyperkalemia is risky if combined with other K⁺-elevating drugs. Always check the medication list.
Clinical pearl, RAAS and ACE inhibitors
Low BP or low Na⁺ delivery → JG cells release renin → angiotensin I → ACE in lungs converts to angiotensin II → vasoconstriction + aldosterone release + ADH release. ACE inhibitors (lisinopril, enalapril) interrupt this loop, lowering BP and reducing Na⁺ retention. Side effect: dry cough from bradykinin buildup.
Mnemonic, Aldosterone
“Aldosterone Adds Na⁺, Dumps K⁺.” Increases sodium reabsorption and potassium secretion in the late distal nephron.
Mnemonic, Loop of Henle
“Descending = Down water. Ascending = Add salts.” Descending limb loses water (filtrate concentrates); ascending limb pumps salts (filtrate dilutes).
Mnemonic, ANP
“Atrium eNcourages Peeing.” ANP from stretched atria opposes RAAS: promotes Na⁺ and water excretion.
Glomerular filtration
- Filtration is driven by glomerular capillary hydrostatic pressure pushing plasma into Bowman's capsule.
- The filtration barrier (endothelium + basement membrane + podocyte slits) excludes proteins and blood cells.
- Damage to podocytes → proteinuria (nephrotic syndrome).
- Sympathetic activation constricts afferent arterioles and reduces GFR (conserves volume).
Segmental reabsorption
- Proximal tubule reabsorbs ~65% of filtered Na⁺ and water plus all glucose and amino acids; secretes H⁺ and many drugs.
- Glucose is reabsorbed via the SGLT (sodium–glucose cotransporter) on the apical membrane.
- Loop of Henle creates the medullary concentration gradient (countercurrent multiplier).
- DCT and collecting duct fine-tune Na⁺, K⁺, and water under hormonal control (aldosterone, ADH).
Hormonal control
- Aldosterone: Na⁺ retention + K⁺ excretion in late DCT/collecting duct.
- ADH (vasopressin): inserts aquaporins in the collecting duct → water retention, concentrated urine.
- Renin: released by juxtaglomerular cells in response to low BP or low NaCl at macula densa; starts RAAS.
- ANP: from atrial stretch, opposes RAAS: natriuresis and diuresis.
Core Recall Check
25 board-style MCQs.
Active recall is the highest-yield study method. Pick an answer, check it, and read why every distractor is wrong.
0 of 25 answered · 0 correct
Keys: A-E or 1-5, Enter to check
- Question 1EasyWhat is the main driving force for glomerular filtration?
- Question 2EasyWhich substances normally do NOT pass the glomerular filter?
- Question 3EasyWhere is the majority of filtered sodium and water reabsorbed?
- Question 4ModerateWhich transporter reabsorbs glucose in the proximal tubule?
- Question 5EasyWhich nephron segment is permeable to water but not solutes?
- Question 6ModerateWhich nephron segment actively reabsorbs Na⁺, K⁺, and Cl⁻ but is impermeable to water?
- Question 7EasyWhich hormone increases Na⁺ reabsorption and K⁺ secretion in the late distal tubule and collecting duct?
- Question 8EasyWhich hormone inserts aquaporins into collecting duct cells to increase water reabsorption?
- Question 9ModerateWhich structure senses decreased renal perfusion and secretes renin?
- Question 10EasyWhich hormone promotes sodium excretion and opposes the renin–angiotensin–aldosterone system?
- Question 11ModerateWhich diuretic class acts at the thick ascending limb of the loop of Henle?
- Question 12ModerateFiltration fraction is best described as:
- Question 13ModerateThe macula densa adjusts glomerular filtration through tubuloglomerular feedback by sensing:
- Question 14HardAn ACE inhibitor lowers glomerular capillary pressure mainly by:
- Question 15HardNSAIDs can reduce GFR in a volume-depleted patient because they:
- Question 16ModerateThiazide diuretics act at the early distal convoluted tubule and characteristically cause:
- Question 17ModerateSpironolactone reduces sodium reabsorption at the collecting duct by:
- Question 18ModerateAcetazolamide acts in the proximal tubule and predisposes to:
- Question 19EasyThe anemia of chronic kidney disease is primarily due to reduced renal production of:
- Question 20ModerateThe final activation step of vitamin D to calcitriol occurs in the:
- Question 21ModerateThe vasa recta help the kidney concentrate urine by:
- Question 22HardParathyroid hormone acts on the kidney to:
- Question 23EasyCreatinine clearance is used clinically to estimate:
- Question 24ModerateFor a patient with advanced CKD, a renally cleared antibiotic should generally be:
- Question 25EasyADH increases urine concentration by:
Clinical Reasoning Cases
INBDE patient cases.
8 ADA INBDE-format patient cases on nephron function. Each case is a shared patient box plus linked questions with full distractor explanations.
INBDE Patient Cases
Nephron Function INBDE Patient Cases →
8 patient cases · 40 linked questions
Open cases →
Author
Dr. Isaac Sun, DDS
Founder, KYT Dental Services. These MCQs are reviewed by a practicing clinician and offered as an educational reference for dental students.
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