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.