# What Do the Kidneys Regulate?

Andrew Bland, MD, FACP, FAAP · October 19, 2026

Kidneys maintain the internal environment through eight linked functions. Filtration is one part of this work; urine is the route through which many adjustments are made.

![Diagram](https://urinenephrology.org/2025_UDPA_Lectures_Live/assets/kidney-regulation-overview-2026-10-19.png)

## Sodium, extracellular volume, and blood pressure

Regulation of total-body sodium helps determine extracellular fluid volume. RAAS promotes sodium retention when effective circulation is low; natriuretic peptides provide a counter-signal.

## Water and tonicity

ADH changes collecting-duct water permeability, helping match water excretion to need. Serum sodium mainly reflects water relative to sodium and potassium; it is not a direct measure of extracellular volume.

## Electrolytes and acid–base balance

The kidneys regulate potassium and magnesium, calcium and phosphate, and acid–base balance. They reclaim filtered bicarbonate and generate new bicarbonate while excreting net acid.

## Endocrine functions

Renal erythropoietin supports red-cell production, and renal activation of vitamin D supports calcium and phosphate homeostasis. These functions can be impaired even when urine output persists.

## Waste and drug clearance

Filtration, secretion, and reabsorption determine the excretion of metabolic wastes and many drugs or metabolites. Creatinine is a useful filtration marker but does not measure every renal function.

## Connect the measurements

Use creatinine/eGFR to discuss filtration, urine albumin to discuss injury and risk, and electrolytes, acid–base status, volume, and endocrine effects to understand the broader picture.

## Supporting evidence

- [NIDDK: Your Kidneys & How They Work](https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work)

## Continue learning

- [Opening lecture: the eight functions](https://urinenephrology.org/2025_UDPA_Lectures_Live/case-based-lectures/opening-lecture.html#regulation)
- [RAAS and kidney effects](https://urinenephrology.org/visual-reference/raas-kidney-effects.html)
- [ADH and kidney effects](https://urinenephrology.org/visual-reference/adh-kidney-effects.html)
- [Creatinine lab and interactive GFR](https://urinenephrology.org/2025_UDPA_Lectures_Live/electrolytes/creatinine-gfr.html#interactive-gfr)
- [Five-session case lecture series](https://urinenephrology.org/2025_UDPA_Lectures_Live/case-based-lectures/index.html)