Kidney anatomy
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kidney anatomy cross section diagram
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nephron structure glomerulus tubule diagram
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Here is a comprehensive overview of kidney anatomy, drawn from Brenner and Rector's The Kidney and Medical Physiology.
Kidney Anatomy
Position & Gross Features
The kidneys are paired, bean-shaped, retroperitoneal organs extending from vertebrae T12 to L3. The right kidney sits slightly more caudal than the left (displaced by the liver).
| Parameter | Males | Females |
|---|---|---|
| Weight | 125–170 g | 115–155 g |
| Length (MRI) | ~12.4 cm | ~11.6 cm |
| Volume | ~202 mL | ~154 mL |
| Thickness | 2.5–3.0 cm | 2.5–3.0 cm |
Each kidney is enclosed in a tough fibrous capsule. On the medial (concave) surface lies the hilum — the gateway for:
- Renal artery (in)
- Renal vein (out)
- Ureter (out)
- Lymphatics
- Nerve plexus
The hilum opens into the renal sinus, a fat-filled space containing the renal pelvis, major and minor calyces, and vessels.
Internal Structure
A bisected kidney reveals two layers:
- Cortex — outer granular region (~1 cm thick); contains glomeruli, convoluted tubules, and cortical columns (columns of Bertin)
- Medulla — inner striated region; composed of 8–18 renal pyramids
Each renal pyramid has:
- Its base at the corticomedullary junction
- Its apex (papilla) pointing toward the renal pelvis
- An area cribrosa at the papilla tip — perforations where collecting ducts (ducts of Bellini) empty urine into minor calyces
One pyramid + its surrounding cortex = one renal lobe
Minor calyces → Major calyces → Renal pelvis → Ureter (28–34 cm long) → Bladder
Vascular Supply
The kidneys receive ~20% of cardiac output, despite being <0.5% of body weight.
Arterial pathway:
Renal artery → Anterior + Posterior branches → Segmental (lobar) arteries → Interlobar arteries → Arcuate arteries (at corticomedullary junction) → Interlobular arteries → Afferent arterioles → Glomerular capillaries → Efferent arterioles → Peritubular capillaries / Vasa recta
There is no collateral circulation between segmental arteries — occlusion causes infarction of the supplied segment.
The Nephron — Functional Unit
Each kidney contains ~900,000–1 million nephrons (range: 200,000–2.5 million). Each nephron consists of:
- Renal corpuscle = Glomerulus + Bowman's capsule
- Proximal convoluted tubule (PCT)
- Loop of Henle (thin descending, thin ascending, thick ascending limb)
- Distal convoluted tubule (DCT)
- Connecting segment → Collecting duct
Two nephron types:
- Superficial (cortical) nephrons — short loops of Henle; efferent arterioles feed peritubular capillaries
- Juxtamedullary nephrons — long loops extending deep into medulla; efferent arterioles form vasa recta (critical for concentrating urine)
Glomerulus
The glomerulus is a tuft of fenestrated capillaries forming the filtration barrier, composed of three layers:
- Fenestrated capillary endothelium (pores 70–100 nm)
- Glomerular basement membrane (GBM)
- Podocyte foot processes with filtration slit diaphragms
Four cellular components of the glomerulus:
- Endothelial cells
- Mesangial cells (structural support + contraction)
- Parietal epithelial cells (line Bowman's capsule)
- Visceral epithelial cells / Podocytes
Juxtaglomerular Apparatus (JGA)
Located at the vascular pole of the glomerulus, the JGA comprises:
- Macula densa — specialized cells of the thick ascending limb that sense tubular NaCl
- Granular (juxtaglomerular) cells in the afferent arteriole wall — secrete renin
- Extraglomerular mesangial cells (lacis cells)
The JGA is the cellular hub of the renin-angiotensin-aldosterone system (RAAS).
Summary Table
| Structure | Location | Key Function |
|---|---|---|
| Cortex | Outer kidney | Filtration, reabsorption |
| Medulla/Pyramids | Inner kidney | Concentration gradient |
| Glomerulus | Cortex | Plasma ultrafiltration |
| Proximal tubule | Cortex | Bulk reabsorption (~65%) |
| Loop of Henle | Medulla | Countercurrent multiplication |
| Distal tubule | Cortex | Fine-tuning Na/K/acid-base |
| Collecting duct | Cortex → Medulla | Water reabsorption (ADH) |
| JGA | Vascular pole | Renin secretion, autoregulation |
| Renal pelvis/Calyces | Sinus | Urine collection/transport |
Sources: Brenner and Rector's The Kidney, 2-Vol Set; Medical Physiology (Boron & Boulpaep); Harrison's Principles of Internal Medicine, 21e
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