Urinary System

Kidneys: Gross Anatomy - Bean Scene Investigation

• Location: Retroperitoneal, T12-L3 (R lower). Size: ~11x6x3cm, ~150g.
• Coverings (In→Out): Capsule, Perinephric fat, Renal fascia, Paranephric fat. 📌 'Cats Prefer Real Prawns'.
• External: Poles (Sup/Inf), Borders (Med/Lat), Surfaces (Ant/Post). Hilum (medial).
• Internal: Cortex; Medulla (Renal Pyramids 8-18); Columns of Bertin; Papilla → Minor Calyces (7-13) → Major Calyces (2-3) → Renal Pelvis.
• Hilum (Ant→Post): Vein, Artery, Pelvis (VAP).

  ⭐ The order of structures in the renal hilum from anterior to posterior is Vein, Artery, Pelvis (VAP).

• Arterial Supply: Renal → Segmental → Lobar → Interlobar → Arcuate → Interlobular. 📌 'Real Sexy Ladies Are Intelligent'.
• Relations (Ant): R: Liver, Duodenum. L: Spleen, Pancreas, Stomach. (Post): Diaphragm, Ribs (R:12th, L:11th/12th).

Kidneys: Microscopic Anatomy - Nephron Ninjas

• Nephron Components: Functional unit of the kidney.
  • Renal Corpuscle: Glomerulus (capillary tuft) + Bowman's Capsule (parietal: simple squamous; visceral: podocytes).
  • Tubules:
    • Proximal Convoluted Tubule (PCT): Simple cuboidal, prominent brush border (microvilli) for reabsorption.
    • Loop of Henle (LoH): Thin segments (simple squamous), Thick ascending limb (simple cuboidal).
    • Distal Convoluted Tubule (DCT): Simple cuboidal, fewer microvilli.

• Nephron Types:

  • Cortical (85%): Short LoH, mainly in cortex; peritubular capillaries.
  • Juxtamedullary (15%): Long LoH deep into medulla; vasa recta; vital for urine concentration.

• Juxtaglomerular Apparatus (JGA): Regulates GFR & blood pressure.

  • Macula Densa: Specialized DCT cells; sense NaCl in tubular fluid.
  • Juxtaglomerular (JG) Cells: Modified smooth muscle cells in afferent arteriole wall; secrete renin.
  • Extraglomerular Mesangial Cells (Lacis cells).

• Collecting System:

  • Collecting Tubules & Ducts (Cortical/Medullary): Lined by:
    • Principal Cells: Reabsorb Na+, secrete K+; ADH-sensitive H2O reabsorption.
    • Intercalated Cells (Type A & B): Acid-base balance (H+/HCO3- transport).

⭐ Juxtaglomerular cells, modified smooth muscle cells in the afferent arteriole wall, secrete renin in response to decreased renal perfusion or low NaCl at macula densa.

Ureters & Bladder - Passage & Pouch

• Ureters
  • Course: Abdominal & pelvic; length ≈25-30 cm.
  • Constrictions (3): Pelviureteric Junction (PUJ), crossing Pelvic brim/iliac vessels, Vesicoureteric Junction (VUJ). 📌 Mnemonic: 'UP on the Border of Vegas'.
  • Blood Supply: Branches from renal, gonadal, aorta, common/internal iliac arteries.
  • Histology: Transitional epithelium, 2-3 layers smooth muscle.
• Bladder
  • Location: Retropubic; Shape: Tetrahedral (empty).
  • Relations: Male (ant. to rectum, sup. to prostate); Female (ant. to uterus/vagina).
  • Parts: Apex, body, fundus/base, neck.
  • Trigone: Smooth area; boundaries: 2 ureteric orifices (superolateral), internal urethral meatus (inferior).
  • Muscle: Detrusor (smooth); Internal urethral sphincter (smooth, involuntary at neck).
  • Ligaments: Pubovesical (females), Puboprostatic (males).

⭐ The three physiological constrictions of the ureter are common sites for calculus impaction: pelviureteric junction, crossing the pelvic brim/common iliac artery, and vesicoureteric junction.

Urethra & Clinical Snippets - Final Flush & Fixes

• Male Urethra:
  • Prostatic: 3-4 cm; urethral crest, prostatic sinus.
  • Membranous: 1-2 cm; urogenital diaphragm, narrowest, least dilatable.
  • Spongy/Penile: 15 cm; corpus spongiosum.
  • Sphincters: Internal (involuntary, bladder neck), External (voluntary, urogenital diaphragm).
• Female Urethra: ≈4 cm; anterior to vagina; ↑UTI susceptibility. Sphincters: Functional internal, external (voluntary).
• Histology: Epithelium transition (e.g., Male: Transitional → Pseudostratified/Columnar → Stratified Squamous; Female: Transitional → Stratified Squamous).
• Innervation (Micturition Control):
  • Parasympathetic (S2-S4): Detrusor contraction, internal sphincter relaxation (Voiding).
  • Sympathetic (T11-L2): Detrusor relaxation, internal sphincter contraction (Filling).
  • Somatic (Pudendal n. S2-S4): External sphincter control.
• Applied Anatomy:
  • Renal calculi sites: Calyces, Pelvi-Ureteric Junction (PUJ), Vesico-Ureteric Junction (VUJ).
  • Benign Prostatic Hyperplasia (BPH) impacts prostatic urethra.
  • Urethral rupture: Bulbous/membranous common.

⭐ The membranous urethra in males is the shortest, least dilatable part, and is most susceptible to injury during pelvic fractures or instrumentation.

High-Yield Points - ⚡ Biggest Takeaways

• Kidneys: retroperitoneal; right lower. Hilum: VAP (Vein, Artery, Pelvis) anterior-posterior.
• JGA (macula densa, JG cells) regulates renin, BP, GFR.
• Ureter constrictions: PUJ, pelvic brim, VUJ (narrowest, common site for calculi).
• Bladder trigone: smooth; detrusor muscle (parasympathetic S2-S4) for voiding.
• Male urethra (≈20cm): prostatic, membranous (narrowest part), spongy. Female urethra (≈4cm): higher UTI risk.
• Horseshoe kidney: commonest fusion anomaly, ascent blocked by IMA (Inferior Mesenteric Artery).