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[Physiology](https://durgical.com/en/physiology/) · [Renal, fluids and acid–base](https://durgical.com/en/physiology/#s-renal)

# Functional anatomy of the nephron

- Concept
- Exam priority: medium

Each kidney has around a million nephrons: a filter (the glomerulus) and a long tube that recovers what is useful and lets waste through.

Updated 2026-11-01

Also called: Nephron, Functional unit of the kidney

**See it in 3D:** [Kidneys](https://durgical.com/en/anatomy/kidney/) · [Renal pelvis](https://durgical.com/en/anatomy/renal-pelvis/) · [Vessels inside the kidney](https://durgical.com/en/anatomy/intrarenal-arteries-and-veins/) · [Left renal artery](https://durgical.com/en/anatomy/renal-artery/) · [Right renal artery](https://durgical.com/en/anatomy/renal-artery-abdomen/) · [Left renal vein](https://durgical.com/en/anatomy/right-renal-vein/) · [Ureters](https://durgical.com/en/anatomy/ureter/)

## Key points

- ≈ 1 million nephrons per kidney (wide range between people); they do not regenerate, and after age 40 they are slowly lost.
- Cortical nephrons (the majority) have short loops; juxtamedullary nephrons (≈ 15–30%) have long loops that build the medullary gradient.
- Order: glomerulus → proximal tubule → descending limb → thin ascending limb → thick ascending limb → macula densa → distal tubule → collecting duct.
- Two capillaries in series: glomerular (high pressure, filters) and peritubular (low pressure, reabsorbs); juxtamedullary nephrons give the vasa recta.
- The kidneys are ≈ 0.4% of body weight but receive ≈ 20–25% of cardiac output.
- The juxtaglomerular apparatus (macula densa + granular cells + extraglomerular mesangium) links the tubule with its own arteriole.

## What it is

The nephron is the kidney's functional unit: a glomerulus that filters and a tubule that modifies the filtrate (proximal tubule, loop of Henle, distal tubule), draining into the collecting duct. Its blood supply is unusual: two capillary beds in series, glomerular and peritubular. The shape and position of each segment explain what it does.

## Key facts

- Arterial path: renal artery → segmental → interlobar → arcuate → cortical radiate → afferent → glomerulus → efferent.
- The proximal tubule has a brush border and many mitochondria: it reabsorbs most of the filtrate.
- The thick limb and distal tubule have many mitochondria but no brush border: active transport without water.
- The collecting duct has principal cells (Na⁺, K⁺, water) and intercalated cells (acid–base).
- The cortex receives ≈ 90% of renal blood flow; the medulla gets little, which makes it sensitive to hypoxia.

### The nephron: segments, transporters and diuretics

**GFR** ≈ 125 mL/min **Filtrate** ≈ 180 L/day **Urine** ≈ 1–2 L/day

Tap a nephron segment: what it reabsorbs, its transporters, the hormones, the diuretics that act there and the classic disorders.

- Glomerulus and arterioles
- Proximal tubule
- Thin descending limb
- Thin ascending limb
- Thick ascending limb
- Distal convoluted tubule
- Collecting tubule and duct
- Juxtaglomerular apparatus (macula densa)
- Cortex
- Medulla
- Interstitial osmolality (≈ 300 → 1200 mOsm/kg)

Illustrative schematic drawn by Durgical (a long-loop juxtamedullary nephron); proportions and percentages are approximate and not for clinical decisions.

## Segments and their function

| Segment | Epithelial feature | Main function |
| --- | --- | --- |
| Glomerulus | Fenestrated endothelium, podocytes | Filters ≈ 180 L/day |
| Proximal tubule | Brush border, mitochondria | Reabsorbs ≈ 65–70% of Na⁺ and water, all glucose |
| Loop of Henle (thin) | Flat epithelium | Passive water and salt exchange |
| Thick ascending limb | Cuboidal, water-tight | Removes NaCl: dilutes and builds the gradient |
| Distal tubule | Cuboidal | Na⁺ (NCC) and Ca²⁺ adjustment |
| Collecting duct | Principal and intercalated cells | Fine tuning: water (ADH), Na⁺/K⁺ (aldosterone), acid |

## Clinical notes

- Nephron loss in chronic kidney disease overloads the survivors (hyperfiltration), which are damaged in turn over time.
- The medulla, with low flow and heavy work, suffers first in ischemia and with some drugs (papillary necrosis from NSAIDs).
- Polycystic kidney disease: cysts arise from the tubule and replace functional tissue.

## Memory aid

'Filter, recover, separate, adjust': the glomerulus filters, the proximal tubule recovers, the loop separates salt from water, the distal tubule and collecting duct adjust.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does the kidney have two capillary beds in series?

The glomerular bed needs high pressure to filter; after the efferent, low hydrostatic and high oncotic pressure in the peritubular capillary favour reabsorption of the filtrate.

## Which nephrons are essential for concentrating urine, and why?

Juxtamedullary nephrons: their long loops reach the inner medulla and, with the vasa recta, build and preserve the osmotic gradient.

## Why is the renal medulla especially sensitive to ischemia?

It receives a small share of renal flow through slow vasa recta, while the thick limb spends a lot of O₂ on active transport.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/physiology/functional-anatomy-of-the-nephron/)

## See it in 3D

The structures of Durgical's 3D anatomy where it happens.

- [Kidneys](https://durgical.com/en/anatomy/kidney/)
- [Renal pelvis](https://durgical.com/en/anatomy/renal-pelvis/)
- [Vessels inside the kidney](https://durgical.com/en/anatomy/intrarenal-arteries-and-veins/)
- [Left renal artery](https://durgical.com/en/anatomy/renal-artery/)
- [Right renal artery](https://durgical.com/en/anatomy/renal-artery-abdomen/)
- [Left renal vein](https://durgical.com/en/anatomy/right-renal-vein/)
- [Ureters](https://durgical.com/en/anatomy/ureter/)

## Related topics

- [Glomerular filtration: the barrier and its determinants](https://durgical.com/en/physiology/glomerular-filtration-the-barrier-and-its-determinants/)
- [Renal blood flow, autoregulation and tubuloglomerular feedback](https://durgical.com/en/physiology/renal-blood-flow-autoregulation-and-tubuloglomerular-feedback/)
- [Transport in the loop of Henle](https://durgical.com/en/physiology/transport-in-the-loop-of-henle/)
- [The countercurrent mechanism, urea recycling and urine concentration](https://durgical.com/en/physiology/the-countercurrent-mechanism-urea-recycling-and-urine-concentration/)
- [Proximal tubule transport](https://durgical.com/en/physiology/proximal-tubule-transport/)
- [Distal tubule and collecting duct](https://durgical.com/en/physiology/distal-tubule-and-collecting-duct/)
- [Micturition and the bladder reflex](https://durgical.com/en/physiology/micturition-and-the-bladder-reflex/)

## Related conditions

- [Chronic kidney disease](https://durgical.com/en/conditions/chronic-kidney-disease/)
- [Acute kidney injury](https://durgical.com/en/conditions/acute-kidney-injury/)
- [Autosomal dominant polycystic kidney disease](https://durgical.com/en/conditions/autosomal-dominant-polycystic-kidney-disease/)

## In Biochemistry

- [Creatinine and estimated glomerular filtration rate (eGFR)](https://durgical.com/en/biochemistry/topics/creatinine-and-estimated-glomerular-filtration-rate/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [25.3 Gross Anatomy of the Kidney](https://openstax.org/books/anatomy-and-physiology-2e/pages/25-3-gross-anatomy-of-the-kidney) (OpenStax (Rice University), 2022); [25.4 Microscopic Anatomy of the Kidney](https://openstax.org/books/anatomy-and-physiology-2e/pages/25-4-microscopic-anatomy-of-the-kidney) (OpenStax (Rice University), 2022); [Anatomy, Abdomen and Pelvis: Kidneys](https://www.ncbi.nlm.nih.gov/books/NBK482385/) (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 26). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/physiology/functional-anatomy-of-the-nephron/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/functional-anatomy-of-the-nephron/