Nephron Filtration & Osmoregulation Lab
Follow filtrate from the glomerulus through the proximal tubule, loop of Henle, distal tubule, and collecting duct. Change blood pressure, ADH, salt intake, hydration, and plasma glucose to see how the kidney controls urine volume, urine concentration, and sodium and glucose handling.
Guided Experiment: How does ADH change urine concentration?
If you raise the ADH level, what happens to urine volume and urine osmolarity?
Write your hypothesis in the Lab Report panel, then click Next.
Controls
Nephron schematic
Filtrate flows glomerulus, proximal tubule, loop of Henle, distal tubule, collecting duct, then urine. The shaded band is the medullary osmotic gradient (about 300 mOsm/L at the cortex to about 1200 mOsm/L deep in the medulla).
Most water and Na⁺ are reabsorbed in the proximal tubule.
The collecting duct sets final urine concentration under ADH.
Filtration results
GFR
125mL/min
Urine output
1.90mL/min
Urine per day
2.73L/day
Urine osmolarity
625mOsm/L
Na⁺ excretion
1429mmol/day
Glucose in urine
None
Classification
Normal urine
Volume by segment (mL/min)
Osmolarity by segment (mOsm/L)
What this means
- Mean arterial pressure is within the autoregulatory range, so GFR stays near 125 mL/min.
- Plasma glucose is below the renal threshold of about 11 mmol/L, so urine is glucose-free.
Data Table
(0 rows)| # | MAP(mmHg) | ADH(%) | Hydration | GFR(mL/min) | Urine(L/day) | Urine osmolarity(mOsm/L) |
|---|
Reference Guide
The Nephron and Its Segments
The nephron is the functional unit of the kidney. Filtrate forms at the glomerulus and is then modified along the tubule before it leaves as urine.
- Glomerulus. Filters plasma to form an isosmotic filtrate.
- Proximal tubule. Reabsorbs the bulk of water and sodium.
- Loop of Henle. Builds the medullary gradient and dilutes the fluid.
- Distal tubule. Fine tunes sodium reabsorption.
- Collecting duct. Sets final urine concentration under ADH.
Water is only reabsorbed along the tubule, so the volume of fluid falls steadily from the glomerulus to the urine.
Glomerular Filtration and GFR Autoregulation
Glomerular filtration rate (GFR) is the volume of plasma filtered per minute, normally about 125 mL/min. It depends on the net filtration pressure across the glomerular capillaries.
Renal autoregulation:
- GFR stays nearly constant between about 80 and 180 mmHg.
- Below 80 mmHg GFR falls steeply toward zero near 40 mmHg.
- This protects filtration across normal pressure swings.
Autoregulation uses the myogenic response and tubuloglomerular feedback to adjust afferent arteriole resistance.
ADH and Water Balance
Antidiuretic hormone (ADH) controls how permeable the collecting duct is to water. It is the main lever for osmoregulation.
- High ADH. Collecting duct reabsorbs more water, giving concentrated, low-volume urine.
- Low ADH. Collecting duct stays water-impermeable, giving dilute, high-volume urine.
- Dehydration. Raises plasma osmolarity and effective ADH to conserve water.
- Overhydration. Lowers effective ADH so excess water is excreted.
Tubular Reabsorption and the Glucose Threshold
Solutes are reabsorbed by transporters that have a maximum rate, called the transport maximum. Glucose is normally reabsorbed completely in the proximal tubule.
- Renal threshold. About 11 mmol/L plasma glucose.
- Glucosuria. Above the threshold, transporters saturate and glucose spills into the urine.
- Sodium. The distal tubule adjusts Na reabsorption to match dietary intake.
Persistent glucosuria is a classic sign of poorly controlled diabetes, where plasma glucose stays above the renal threshold.
