Kidneys and Suprarenal Glands

Kidneys - Bean Scene Investigation

• Location: Retroperitoneal, T12-L3. Right kidney typically lower. Hilum of left kidney near transpyloric plane (L1).
• Size & Weight: Approx. 11x6x3 cm; 135-150 g.
• Coverings (inward to outward):
  • Fibrous capsule (true capsule)
  • Perirenal fat (adipose capsule)
  • Renal fascia (Gerota's fascia) - encloses kidney & suprarenal gland (separated by a thin septum)
  • Pararenal fat (posteriorly)
• Posterior Relations: Diaphragm, Transversus abdominis, Iliacus, Psoas major, Quadratus lumborum muscles; Subcostal (T12), Iliohypogastric (L1), & Ilioinguinal (L1) nerves/vessels. 📌 Mnemonic: 'D TITS L'.
• Anterior Relations:

  Right Kidney	Left Kidney
  Suprarenal, Liver, Duodenum (2nd)	Suprarenal, Stomach, Spleen
  Hepatic flexure (Colon), Jejunum	Pancreas (tail), Splenic flexure (Colon), Jejunum

⭐ The hilum of the left kidney lies near the transpyloric plane (L1), about 5 cm from the midline.

Kidneys - Inside Story & Plumbing

• Hilum: Structures anterior to posterior: Renal Vein, Renal Artery, Renal Pelvis (VAP 📌).
• Renal Sinus: Fat-filled central cavity; houses renal vessels, nerves, calyces, and pelvis.
• Internal Structure:
  • Outer Cortex: Contains glomeruli, convoluted tubules, cortical collecting ducts. Extends into medulla as renal columns of Bertin.
  • Inner Medulla: Composed of 8-18 renal pyramids; apex is renal papilla, projecting into a minor calyx. Each papilla drains into one of 7-14 minor calyces.
• Collecting System (Urine Flow): Minor calyces merge to form 2-3 major calyces, then the renal pelvis.

• Renal Segments: 5 segments based on arterial supply: Apical, Anterosuperior, Anteroinferior, Posterior, Inferior.

⭐ Renal columns (of Bertin) are inward extensions of cortical tissue that separate the renal pyramids.

Kidneys - Red Rivers & Wires

• Arterial Supply: Abd. Aorta (L1-L2) → Renal arteries → 5 Segmental (end arteries) → Lobar → Interlobar (renal columns) → Arcuate (corticomedullary jn.) → Interlobular (cortex) → Afferent arterioles.
• Venous Drainage: Stellate veins → Interlobular → Arcuate → Interlobar → Segmental → Renal vein → IVC.
  • 📌 Left renal vein: longer, anterior to Aorta, posterior to SMA; receives left suprarenal & gonadal veins.
• Lymphatics: Lateral aortic (paraaortic/lumbar) nodes.
• Nerves: Renal plexus (around renal artery).
  • Sympathetic (T10-L1/L2, least splanchnic): vasoconstriction, ↑ renin.
  • Parasympathetic (Vagus): function less clear.

⭐ The segmental arteries of the kidney are anatomical end arteries; their occlusion can lead to infarction of the renal segment they supply.

Suprarenals - Adrenal Rush Hour

• Location: Retroperitoneal, superomedial to kidneys, within renal fascia (but separate).
• Shape: Right: pyramidal; Left: semilunar.
• Parts & Origin:
  • Cortex (mesoderm): 📌 Mnemonic 'GFR - Salt, Sugar, Sex'

    Zone	Product (e.g.)	Primary Role
    Glomerulosa	Mineralocorticoids (Aldosterone)	Salt balance
    Fasciculata	Glucocorticoids (Cortisol)	Sugar metabolism
    Reticularis	Androgens	Sex hormones

  • Medulla (neural crest): Chromaffin cells (modified postganglionic sympathetic neurons) secrete Catecholamines (Adrenaline, Noradrenaline).
• Arterial Supply (Rich): 📌 Superior (from inferior phrenic a.), Middle (from abdominal aorta), Inferior (from renal a.).
• Venous Drainage (Single vein/gland): 📌 Right suprarenal v. → IVC; Left suprarenal v. → Left renal v.
• Lymphatics: Lumbar (para-aortic) nodes.
• Nerve Supply: Preganglionic sympathetic fibers (splanchnic nerves) to medullary chromaffin cells.

⭐ The left suprarenal vein drains into the left renal vein, then to IVC; the right suprarenal vein drains directly into the IVC.

High‑Yield Points - ⚡ Biggest Takeaways

• Kidneys: Retroperitoneal, T12-L3 level; right kidney slightly lower.
• Renal hilum (anterior to posterior): Vein, Artery, Pelvis (VAP).
• Left suprarenal vein → left renal vein; Right suprarenal vein → IVC.
• Suprarenal cortex (GFR): Glomerulosa (Aldosterone), Fasciculata (Cortisol), Reticularis (Androgens).
• Suprarenal medulla: Chromaffin cells secrete catecholamines.
• Nutcracker syndrome: Left renal vein compression by SMA and Aorta.
• Horseshoe kidney: Ascent blocked by Inferior Mesenteric Artery.