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Physiology · Renal, fluids and acid–base

Renal blood flow, autoregulation and tubuloglomerular feedback !

  • Regulation
  • Exam priority: medium

The kidney keeps its flow and filtration nearly constant even when blood pressure rises or falls a lot, by narrowing or widening its inflow arteriole.

Updated 2026-11-01

Also called: Macula densa, Myogenic response

See it in 3D: Right renal artery · Left renal artery · Vessels inside the kidney · Kidneys

What it is

Renal blood flow (≈ 1.1–1.2 L/min) and GFR stay nearly constant between ≈ 75 and 160 mmHg of mean arterial pressure. Two mechanisms do this at the afferent arteriole: the myogenic response of smooth muscle and tubuloglomerular feedback from the macula densa. Outside that range, or with strong sympathetic drive, flow follows pressure.

How it works, step by step

  1. Arterial pressure rises, stretching the wall of the afferent arteriole more.
  2. Smooth muscle responds by contracting within seconds (myogenic response), limiting the rise in glomerular pressure.
  3. If GFR still rises, more NaCl reaches the macula densa at the end of the thick limb.
  4. The macula densa takes up NaCl via NKCC2 and releases ATP, converted to adenosine (A1 receptors): the afferent constricts.
  5. That nephron's GFR returns to baseline and NaCl delivery to the distal tubule normalises.
  6. If pressure falls, the reverse happens: the afferent dilates, renin is released and angiotensin II constricts the efferent to sustain GFR.

The nephron: segments, transporters and diuretics

The nephron: segments, transporters and diuretics CortexOuter medullaInner medulla3006009001200mOsm/kgUrineGlomerulusProximal tubuleDistal tubuleThin descendingThin ascendingThick ascendingCollecting ductJuxtaglomerularapparatusNHE3 · SGLT2Filters ≈ 180 L/dayAQP1Passive NaClNKCC2 · ROMKParacellular Ca²⁺, Mg²⁺NCC · Ca²⁺ (PTH)ENaC · ROMK/BKAQP2 (ADH)α: H⁺-ATPase · β: pendrin

Juxtaglomerular apparatus (macula densa) NaCl sensor · releases renin

Juxtaglomerular apparatus (macula densa)

  • What it does: The macula densa, at the end of the thick limb, senses the NaCl arriving: more NaCl constricts the afferent arteriole (tubuloglomerular feedback, adenosine) and curbs renin; less NaCl stimulates renin. Granular (juxtaglomerular) cells of the afferent arteriole secrete renin.
  • Transporters: NKCC2 in the macula densa (the NaCl sensor).
  • Hormones: Renin release: lower afferent pressure, less NaCl at the macula densa and sympathetic (β1) input. Renin → Ang I → Ang II (ACE) → aldosterone.
  • Drugs: Beta blockers lower renin; loop diuretics blind the sensor (more renin); ACE inhibitors, ARBs and direct renin inhibitors block the axis.
  • Disorders: Renal artery stenosis (renovascular hypertension with high renin); juxtaglomerular cell tumor (rare).
  • 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.

The nephron: segments, transporters and diuretics

The nephron: segments, transporters and diuretics CortexOuter medullaInner medulla3006009001200mOsm/kgUrineGlomerulusProximal tubuleDistal tubuleThin descendingThin ascendingThick ascendingCollecting ductJuxtaglomerularapparatusNHE3 · SGLT2Filters ≈ 180 L/dayAQP1Passive NaClNKCC2 · ROMKParacellular Ca²⁺, Mg²⁺NCC · Ca²⁺ (PTH)ENaC · ROMK/BKAQP2 (ADH)α: H⁺-ATPase · β: pendrin

Glomerulus and Bowman capsule Filters ≈ 180 L/day · GFR ≈ 125 mL/min

Glomerulus and Bowman capsule

  • What it does: Filters plasma: ≈ 180 L/day (GFR ≈ 125 mL/min), filtration fraction ≈ 20%. The barrier (fenestrated endothelium, negatively charged basement membrane and podocytes with slit diaphragms) lets water and small solutes through, not cells or most proteins.
  • Transporters: No transporters: Starling forces drive it (capillary hydrostatic pressure for; capsule pressure and plasma oncotic pressure against).
  • Hormones: Ang II constricts the efferent arteriole more (holds GFR up); prostaglandins dilate the afferent; autoregulation (myogenic and tubuloglomerular feedback) keeps GFR steady.
  • Drugs: NSAIDs (afferent constriction) and ACE inhibitors or ARBs (efferent dilation) can lower GFR.
  • Disorders: Nephritic syndrome (hematuria, inflammation) and nephrotic syndrome (proteinuria > 3.5 g/day, podocyte injury).
  • 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.

Reference values

ParameterValueNote
Renal blood flow≈ 1.1–1.2 L/min≈ 20–25% of cardiac output
Renal plasma flow≈ 625 mL/min
Autoregulatory range≈ 75–160 mmHgmean arterial pressure
Renal O₂ consumptionhigh and proportional to Na⁺ reabsorbed

Approximate values for a healthy adult at rest; each laboratory sets its own ranges.

Regulation

  • −Myogenic response: Constricts the afferent when pressure rises; dilates it when pressure falls.
  • −Tubuloglomerular feedback: More NaCl at the macula densa → afferent constricts → ↓ GFR.
  • −Renal sympathetic nerves (α1): Constrict both arterioles: ↓ flow and ↓ GFR in hemorrhage.
  • +Prostaglandins, nitric oxide, bradykinin: Dilate the afferent: ↑ flow and GFR.
  • +Angiotensin II (physiological levels): Mainly constricts the efferent: sustains GFR when pressure falls.
  • +Dietary protein, hyperglycemia: Raise GFR (more proximal reabsorption → less NaCl at the macula densa).

Clinical notes

  • In chronic hypertension the autoregulation curve shifts right, so lowering pressure very fast can reduce GFR.
  • In shock, pressure falls below the range and the sympathetic system closes the arterioles: prerenal acute kidney injury, then tubular necrosis.
  • Early diabetes and very high-protein diets raise GFR through tubuloglomerular feedback (hyperfiltration).
  • NSAIDs in a patient whose flow depends on prostaglandins (heart failure, cirrhosis, older adults) can precipitate acute kidney injury.

Test yourself

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

What does the macula densa sense, and how does GFR change in response?

It senses NaCl reaching the end of the thick limb (via NKCC2). If much arrives, it releases ATP/adenosine, constricts the afferent and lowers GFR; if little arrives, it dilates the afferent and releases renin.

Why can loop diuretics raise renin?

They block NKCC2 in the macula densa, which then cannot 'sense' NaCl: it reads delivery as low and stimulates renin release.

Why does hyperglycemia raise GFR in early diabetes?

More glucose is reabsorbed with Na⁺ through proximal SGLTs, less NaCl reaches the macula densa and feedback dilates the afferent: hyperfiltration.

Why doesn't autoregulation protect the kidney in hypovolemic shock?

Pressure falls below the range (≈ 75 mmHg) and the sympathetic system constricts the arterioles; flow becomes pressure-dependent and GFR falls.

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

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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: 25.7 Regulation of Renal Blood Flow (OpenStax (Rice University), 2022); Acute Kidney Injury (StatPearls (NCBI Bookshelf), 2024); Anatomy, Abdomen and Pelvis, Renal Artery (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 27). 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.