Nephron Function — INBDE Review
Glomerular filtration, segmental reabsorption (PCT, loop, DCT, collecting duct), aldosterone/ADH/ANP regulation, and how diuretics map onto nephron sites. 11 board-style MCQs.
Concept summary & clinical relevance.
Quick-reference structure first, then nerve-by-nerve detail. 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.
| 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 |
| 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 |
| 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 |
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.
11 board-style MCQs.
Active recall is the highest-yield study method for the INBDE. Pick an answer, check it, and read why every distractor is wrong — that's where the learning compounds.
The MCQs above are Core Recall — testing what you've memorized. The book adds a full Clinical Integration set: board-style patient scenarios where you apply this anatomy to real clinical reasoning. That's the section the INBDE actually weights heaviest.
- 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?
900 INBDE-style MCQs with full explanations across 18 chapters — Core Recall plus board-style Clinical Integration scenarios — alongside Learning Summaries, Integration Bridges, and Review Boxes. Built by Dr. Isaac Sun for dental students who want to think like a clinician, not just memorize.
Founder, KYT Dental Services · Author, KYT INBDE series. These MCQs and Learning Summaries are part of a structural-thinking framework Dr. Sun uses with patients in the chair.