# Renal Anatomy and Physiology: Follow Blood and Filtrate

Localize a problem by following blood flow, then filtrate, then the transport process that fails.

![Infographic: Renal Anatomy and Physiology: Follow Blood and Filtrate](https://urinenephrology.org/visual-reference/images/student-renal-anatomy.png?v=20261003c)

## Blood and filtrate take different routes

Blood: renal artery → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta. Filtrate: Bowman space → proximal tubule → loop → distal tubule → collecting duct → pelvis.

## Proximal tubule: bulk reclamation

Reclaims filtered glucose, amino acids, bicarbonate, sodium, and water. Normoglycemic glycosuria plus phosphate and bicarbonate wasting suggests proximal dysfunction (Fanconi pattern), rather than isolated glomerular filtration loss.

## Loop: separate salt from water

The descending limb permits water movement. The thick ascending limb reabsorbs salt through NKCC2 but is water-impermeable. Loop diuretics block NKCC2 and impair the medullary concentrating gradient.

## Distal tubule: a thiazide target

The distal convoluted tubule reabsorbs NaCl through NCC. Thiazides inhibit NCC; the resulting distal sodium delivery can increase potassium loss. Check sodium and potassium after starting or changing treatment.

## Collecting duct: final regulation

Aldosterone promotes ENaC-mediated sodium uptake and potassium secretion. Vasopressin inserts aquaporin-2 water channels. Thus potassium excretion and water conservation can change without an equivalent change in GFR.

## Apply the map

Polyuria with dilute urine asks about water intake, vasopressin, and concentrating ability. Albuminuria with red-cell casts asks about glomerular injury. Urine volume alone cannot tell you whether filtration or tubular function is normal.

## Supporting evidence

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

## Source lessons

- [chapter 02 anatomy](https://urinenephrology.org/nephrology-textbook/chapters/chapter-02-anatomy.html)
- [renal anatomy histology student handout](https://urinenephrology.org/student-resources/foundations/renal-anatomy-histology-student-handout.html)
- [renal physiology student handout](https://urinenephrology.org/student-resources/foundations/renal-physiology-student-handout.html)

Read alongside the full lessons; the findings and decisions shown here require the stated clinical context.