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Healthcare · Interactive model

How your kidneys turn blood into urine.

Healthy kidneys filter 150–180 liters of plasma a day and return all but one or two liters to the blood. Adjust diet, hydration and body parameters below to see how the urine they produce changes.

Whole-body water balance

L/day
IN3.0 Ldrinks 2.0 + food 1.0BREATH + SKIN0.8 LSWEAT0.4 LFILTERED158 L98.9% returnedto the bloodURINE1.70 L440 mOsm/kgSTOOL0.1 L

The urine this produces

24-hour
Volume1.70 L
Color Straw yellow
Specific gravity1.013
pH6.1
Osmolality440 mOsm/kg normal
Sodium127 mmol/day normal
Potassium57 mmol/day normal
Urea257 mmol/day normal
Creatinine1400 mg/day normal
Glucose0.00 g/day normal

Inside one nephron

~1 million per kidney
blood1234
  1. 1
    Filtered158 L100% of filtrate left

    Blood pressure pushes plasma through a filter; cells and proteins stay behind.

  2. 2
    After proximal tubule55 L35% of filtrate left

    Takes back ~65% of water and salt, and all glucose (below threshold).

  3. 3
    After loop of henle32 L20% of filtrate left

    Builds the salt gradient that lets urine be concentrated.

  4. 4
    Urine1.70 L1.1% of filtrate left

    Hormones (ADH, aldosterone) set the final water and salt.

What the blood shows

steady state
Blood urea nitrogen9.7 mg/dL normal
Serum creatinine0.80 mg/dL normal
Plasma filtered
158 L/day
Water reabsorbed
98.9%
Sodium excreted (FENa)
0.57%
Max concentration
1200 mOsm/kg

What MobileSense would see

illustrative SERS spectrum
Uric acid 640Creatinine 680Urea 10036008001000120014001600cm⁻¹

Peak positions are approximate Raman bands for each molecule. Peak heights scale with the modeled concentration, so dilute urine gives smaller peaks and high blood sugar brings up a glucose band. Real SERS intensities also depend on each molecule's affinity for the gold surface.

How the model works

A simplified, steady-state body.

Over a typical day, the body stays in balance: what goes in must come out. The kidneys get whatever is left after sweat, breath and stool, and they adjust how much water and salt they reabsorb to keep blood composition stable.

That is what makes urine informative. Its volume and chemistry reflect what you ate and drank, how active you were, your blood sugar, and how well your kidneys are working.

← Back to Healthcare

  • Steady state: each day's urinary excretion of sodium, potassium, urea and creatinine equals intake or production minus losses in sweat and stool.
  • Water: urine volume = drinks + water in food (0.7 L) + metabolic water (0.3 L) − breath and skin (0.8 L, 1.3 L when hot) − stool (0.1 L) − sweat (0.8 L/h of vigorous exercise, 1.3 L/h when hot).
  • Urine volume is bounded by how concentrated (up to 1200 mOsm/kg, lower with reduced GFR) or dilute (down to 50 mOsm/kg) the kidneys can make it.
  • Urea comes from dietary protein (16% nitrogen), minus ~4 g/day of nitrogen lost by other routes. Creatinine comes from muscle (~20 mg/kg/day).
  • Glucose is fully reabsorbed until blood glucose passes the ~180 mg/dL renal threshold.
  • Blood urea and creatinine are the levels needed for the given GFR to clear the day's load.
  • Urine pH comes from the diet's net acid load: protein adds acid, potassium-rich produce adds base (Frassetto NEAP estimate). Specific gravity ≈ 1 + osmolality / 35,000.

Educational model for a generic healthy adult with rounded textbook values. It is not a diagnostic tool and should not guide medical decisions.

Measure real urine chemistry, continuously.

MobileSense captures SERS spectra of urine automatically, with no test strips or disposables.

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