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Related Concept Videos

Physiology of the Genitourinary System II: Tubular Reabsorption and Secretion01:22

Physiology of the Genitourinary System II: Tubular Reabsorption and Secretion

The kidneys maintain homeostasis through filtration, reabsorption, and secretion. Tubular reabsorption and secretion are crucial in forming urine and regulating electrolytes, water balance, and waste elimination.Tubular Reabsorption and Secretion ProcessesTubular reabsorption is the process that reclaims essential substances such as electrolytes, glucose, amino acids, and water from the glomerular filtrate back into the bloodstream. This is achieved through passive and active transport...
Renal Drug Excretion: Tubular Secretion01:28

Renal Drug Excretion: Tubular Secretion

Active tubular secretion is a robust, energy-demanding process that utilizes carrier systems to transport drugs into renal tubules. The active renal secretion systems include the organic anion transporter (OAT) for weak acids and the organic cation transporter (OCT) for weak bases. Structurally similar drugs can compete for the same transporter, potentially leading to drug accumulation and toxicity. However, this principle can be exploited therapeutically. One example is probenecid (Probalan),...
Renal Drug Excretion: Tubular Reabsorption01:25

Renal Drug Excretion: Tubular Reabsorption

Tubular reabsorption, a process occurring post-glomerular filtration of drugs in the renal tubule, is a critical determinant of drug half-life. During the process of renal excretion, as the glomerular filtrate progresses to the distal convoluted tubule (DCT), drugs that are highly permeable, lipophilic, and nonionized undergo passive reabsorption from the tubular fluid into the surrounding peritubular capillaries. This reabsorption process restricts their elimination through the kidneys. This...
Tubular Reabsorption and Secretion01:28

Tubular Reabsorption and Secretion

Tubular secretion and reabsorption are two critical processes in the nephron tubule of the kidneys. When the fluid filtered from the glomerulus enters the proximal convoluted tubule, it is referred to as filtrate, and its composition changes due to tubular reabsorption and secretion.
Tubular reabsorption is a selective process that starts when the filtrate enters the proximal tubules. It involves substances traveling through the transcellular route (through the tubule cell and peritubular...
Reabsorption and Secretion in the Loop of Henle01:17

Reabsorption and Secretion in the Loop of Henle

The thick ascending limb of the nephron loop has Na+–K+–2Cl− symporters in the apical membranes of its cells. These symporters simultaneously reclaim one sodium ion, one potassium ion, and two chloride ions from the tubular fluid. Sodium ions are actively transported into the interstitial fluid at the base and sides of the cell, diffusing into the vasa recta. Chloride ions move through leakage channels in the basolateral membrane into the interstitial fluid and then into the vasa recta.
Physiology of the Genitourinary System III: Urine Concentration and Dilution01:20

Physiology of the Genitourinary System III: Urine Concentration and Dilution

The kidneys concentrate or dilute urine to maintain water and electrolyte balance. Nephrons, particularly the loop of Henle, play a crucial role in this process through the countercurrent multiplication system. This system establishes a high osmolarity in the renal medulla, which is essential for water reabsorption. In the loop of Henle’s descending limb, water is reabsorbed into the surrounding medulla due to its permeability to water. In contrast, the ascending limb actively transports...

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Related Experiment Video

Updated: May 16, 2026

Isolation of Primary Human Proximal Tubule Epithelial Cells and Their Use in Creating a Microphysiological Model of the Renal Proximal Tubule
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Mechanistic models describing active renal reabsorption and secretion: a simulation-based study.

Melanie A Felmlee1, Rutwij A Dave, Marilyn E Morris

  • 1Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, The State University of New York, Buffalo, NY 14214, USA.

The AAPS Journal
|December 1, 2012
PubMed
Summary

This study highlights that accurate Vmax estimates are crucial for pharmacokinetic models of renal drug clearance. In vitro Vmax data requires scaling for reliable in vivo predictions.

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Area of Science:

  • Pharmacokinetics
  • Renal drug transport
  • Mathematical modeling

Background:

  • Active renal secretion and reabsorption significantly influence drug clearance.
  • Mechanistic pharmacokinetic models are essential for predicting drug behavior.
  • Understanding the impact of Michaelis-Menten parameters on renal clearance is vital.

Purpose of the Study:

  • To evaluate mechanistic pharmacokinetic models for active renal secretion and reabsorption.
  • To assess the influence of Michaelis-Menten parameter variability on renal clearance (CL(r)).
  • To determine the importance of Vmax and Km estimates in pharmacokinetic modeling.

Main Methods:

  • Simulated plasma concentration and urinary excretion profiles.
  • Calculated renal clearance (CL(r)) for reabsorption (R1/R2), secretion (S1/S2), and combined models.
  • Varied doses (1-1,000 mg/kg) and Michaelis-Menten parameters (Vmax, Km) over a 100-fold range.

Main Results:

  • Reabsorption models (R1/R2) showed similar CL(r) despite parameter variations.
  • Secretion models (S1/S2) exhibited similar parameter-CL(r) relationships, with S1 yielding higher CL(r).
  • Vmax perturbations caused the most significant CL(r) changes across models; intrinsic clearance failed to predict consistent CL(r).

Conclusions:

  • Accurate Vmax estimation is critical for determining renal clearance in pharmacokinetic models.
  • While Km can be obtained from in vitro studies, Vmax requires in vitro/in vivo extrapolation.
  • Renal clearance is dose-dependent, influenced by secretion at low doses and unbound fraction at high doses.