Study smarter with Fiveable
Get study guides, practice questions, and cheatsheets for all your subjects. Join 500,000+ students with a 96% pass rate.
The nephron is where the magic of kidney function actually happens—it's the structural and functional unit that transforms blood into urine through a carefully orchestrated sequence of filtration, reabsorption, and secretion. When you're tested on renal physiology, you're really being asked to demonstrate that you understand how each nephron segment contributes to homeostasis: maintaining fluid balance, regulating electrolytes, controlling blood pressure, and eliminating metabolic waste. These aren't isolated concepts—they connect directly to cardiovascular physiology, acid-base balance, and hormonal regulation.
Don't just memorize the parts in order like a shopping list. Instead, focus on what each structure does and why its unique features make that function possible. Ask yourself: Is this segment about filtering, reabsorbing, secreting, or regulating? What makes it permeable or impermeable? What hormones act here? When you can answer those questions, you'll nail both multiple-choice questions and FRQs that ask you to trace a molecule's journey or explain how the kidney responds to dehydration.
The nephron's first job is to create filtrate from blood plasma. This happens in the renal corpuscle, where high pressure forces water and small solutes out of the blood while retaining cells and large proteins. The key principle here is pressure-driven bulk filtration across a selectively permeable barrier.
Compare: Afferent vs. efferent arteriole—both regulate GFR, but afferent controls blood entering the glomerulus while efferent controls blood leaving. Constricting the afferent decreases GFR; constricting the efferent increases it. If an FRQ asks how angiotensin II maintains GFR during hypotension, efferent constriction is your answer.
After filtration, the nephron must recover valuable substances before they're lost in urine. The proximal convoluted tubule handles the heavy lifting, reabsorbing most filtered water, sodium, glucose, and amino acids. This segment prioritizes quantity over fine-tuning—it's about getting back what the body can't afford to lose.
Compare: PCT vs. DCT—both are convoluted tubules, but the PCT handles bulk reabsorption (~65-70% of filtrate) with extensive microvilli, while the DCT fine-tunes electrolytes under hormonal control with fewer microvilli. Think of PCT as "wholesale" and DCT as "retail."
The kidney's ability to produce concentrated urine depends entirely on the osmotic gradient in the renal medulla. The Loop of Henle and its parallel blood supply (vasa recta) work together through countercurrent mechanisms to establish and maintain this gradient. Without this system, you couldn't conserve water during dehydration.
Compare: Countercurrent multiplier (Loop of Henle) vs. countercurrent exchanger (vasa recta)—the Loop creates the medullary gradient through active transport, while the vasa recta preserves it through passive exchange. Both require parallel, opposite-flow arrangements, but one is active and one is passive.
The distal nephron segments—DCT and collecting duct—make final adjustments to urine composition based on the body's current needs. These segments respond to hormones like aldosterone, ADH, and parathyroid hormone to precisely regulate electrolyte and water balance. This is where homeostatic feedback loops meet nephron anatomy.
Compare: DCT vs. collecting duct—both respond to hormones, but DCT primarily handles electrolytes (aldosterone, PTH) while the collecting duct primarily handles water (ADH). An FRQ about dehydration response should focus on ADH and the collecting duct; one about hyperkalemia should focus on aldosterone and the DCT.
The peritubular capillaries form a low-pressure network that receives everything the tubules reabsorb and delivers substances for secretion. These capillaries complete the circuit—without them, reabsorbed materials would have nowhere to go.
Compare: Peritubular capillaries vs. vasa recta—both are post-glomerular capillaries, but peritubular capillaries serve cortical nephrons and handle general reabsorption/secretion, while vasa recta serve juxtamedullary nephrons and specifically preserve the medullary gradient. Location determines function.
The juxtaglomerular apparatus acts as a sensor-effector unit that monitors filtrate composition and blood pressure, then adjusts nephron function accordingly. This structure integrates local feedback with systemic hormonal control.
Compare: JGA vs. baroreceptors—both sense pressure changes, but the JGA monitors renal perfusion and responds by releasing renin (hormonal), while arterial baroreceptors monitor systemic pressure and respond via autonomic reflexes (neural). The JGA provides slower, sustained regulation; baroreceptors provide rapid adjustments.
| Concept | Best Examples |
|---|---|
| Filtration | Glomerulus, Bowman's capsule, afferent/efferent arterioles |
| Bulk reabsorption | Proximal convoluted tubule |
| Concentration gradient | Loop of Henle (descending/ascending), vasa recta |
| Hormonal fine-tuning | Distal convoluted tubule, collecting duct |
| Water balance (ADH) | Collecting duct |
| Electrolyte regulation (aldosterone) | DCT, collecting duct |
| Countercurrent mechanisms | Loop of Henle (multiplier), vasa recta (exchanger) |
| GFR regulation | Afferent arteriole, efferent arteriole, JGA |
Which two nephron segments are impermeable to water, and how does this impermeability serve different functions in each?
A patient has low ADH levels. Which nephron structure will be most affected, and what will happen to urine concentration?
Compare the roles of the afferent and efferent arterioles in regulating GFR. How would constricting each one differently affect filtration?
The Loop of Henle and vasa recta both use countercurrent arrangements. Explain how one creates the medullary gradient while the other preserves it.
An FRQ asks you to trace the path of a glucose molecule from the glomerulus back to the bloodstream. Which structures are involved, and what transport mechanisms move glucose at each step?