Structure and function of the renal system and prostate

The nephron and investigation

The kidney's core functional unit is the nephron (glomerulus + tubule) - ~1 million per kidney, performing filtration (glomerulus), reabsorption/secretion (tubule), and endocrine functions (EPO, renin, activated vitamin D)
Investigation of renal structure and function combines blood tests (eGFR, electrolytes), urine tests (urinalysis, ACR), and imaging (ultrasound first-line)

Nephron number is fixed after birth (no regeneration) - lower nephron number at birth (e.g. from prematurity/low birth weight) is an independent risk factor for CKD/hypertension in later life

Segment	Main function
Glomerulus	Filtration barrier (size + charge selective)
Proximal tubule	Bulk reabsorption - ~65% filtered Na/water, all filtered glucose/amino acids, bicarbonate reclamation
Loop of Henle	Countercurrent multiplication - generates the medullary concentration gradient
Distal tubule/collecting duct	Fine-tuning - ADH-regulated water reabsorption, aldosterone-regulated Na/K exchange, acid-base regulation

First-line: eGFR/creatinine, electrolytes, urinalysis +/- ACR, renal tract ultrasound - covers the great majority of presentations
Second-line/targeted: 24-hour urine studies, immunology (ANA, ANCA, complement, anti-GBM) if glomerulonephritis is suspected, renal biopsy for histological diagnosis when the cause remains unclear or management hinges on the result
Investigation strategy is staged and hypothesis-driven - moving from first-line tests to targeted second-line testing based on the pattern found (glomerular vs tubular vs obstructive vs vascular), not a fixed panel for every patient

CKD staging, glomerulonephritis workup, obstructive uropathy, renal biopsy indications

Fixed nephron number means renal reserve, not baseline function alone, determines resilience to a second insult (e.g. why a single kidney or a low-birth-weight patient tolerates AKI worse)

5 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.