# RAAS: From Low Effective Circulation to Kidney Response

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

RAAS links a signal of low effective circulation to vascular tone, sodium retention, and aldosterone-mediated potassium and hydrogen-ion secretion.

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

## What starts the signal?

Reduced renal perfusion pressure, reduced macula-densa sodium chloride delivery, and sympathetic beta-1 stimulation can promote renin release from juxtaglomerular cells.

## Follow the pathway

Liver-derived angiotensinogen is cleaved by renin to angiotensin I; ACE converts angiotensin I to angiotensin II. Angiotensin II stimulates adrenal aldosterone secretion.

## Angiotensin II acts before the distal nephron

Angiotensin II promotes proximal sodium reabsorption and vasoconstriction. Preferential efferent constriction can help preserve glomerular pressure during reduced perfusion; strong activation can also reduce renal blood flow and GFR.

## Aldosterone changes distal handling

Aldosterone promotes distal sodium reabsorption, potassium secretion, and hydrogen-ion secretion. Elevated potassium can directly stimulate aldosterone independently of renin.

## Apply it to edema and filtration

A patient can have excess total-body fluid yet low effective arterial circulation. Connect this to sodium retention and ADH, then use the GFR model to discuss why ACE inhibitors or ARBs can alter glomerular pressure.

## Supporting evidence

- [NIDDK: Your Kidneys & How They Work](https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work)
- [Primary study: angiotensin II and proximal sodium transport](https://www.jci.org/articles/view/111237)

## Continue learning

- [Opening lecture: RAAS](https://urinenephrology.org/2025_UDPA_Lectures_Live/case-based-lectures/opening-lecture.html#raas-diagram)
- [Interactive glomerular hemodynamics](https://urinenephrology.org/2025_UDPA_Lectures_Live/electrolytes/creatinine-gfr.html#interactive-gfr)
- [Edema lecture](https://urinenephrology.org/2025_UDPA_Lectures_Live/edema/index.html)
- [Cardiorenal disease lecture](https://urinenephrology.org/2025_UDPA_Lectures_Live/cardiorenal-disease/index.html)
- [ADH and kidney effects](https://urinenephrology.org/visual-reference/adh-kidney-effects.html)