Untitled Quiz

Urinary System Histology

• The urinary system comprises paired kidneys, ureters, urinary bladder, and urethra.

Kidney Structure

• The kidney is a bean-shaped retroperitoneal organ.
• It's composed of:
  • Stroma:
    • Capsule: Dense connective tissue surrounded by adipose tissue (peri-renal fat).
    • Renal interstitium: Intertubular, extraglomerular, extravascular space within the kidney.
    • Minimal connective tissue between parenchymal cells.
  • Parenchyma: Functional tissue of the kidney, distinct from connective tissue.
    • Outer Cortex
    • Inner Medulla
• The kidney's histological structure includes calyces, renal pelvis, minor and major calyces.

Uriniferous Tubule

• The structural unit of the kidney is the nephron and a collecting tubule.
• The nephron produces urine.
• The collecting tubules concentrate urine and transport it to the calyces.

Nephron

• The basic functional unit of the kidney is the nephron.
• Each kidney contains millions of nephrons (1-4 million).
• Nephron components:
  • Renal (Malpighian) corpuscle
  • Proximal convoluted tubule
  • Loop of Henle
  • Distal convoluted tubule

Renal Corpuscle

• The renal corpuscle is composed of:
  • Glomerulus: A vascular ball (approximately 200 µm in diameter) covered by Bowman's capsule.
  • Bowman's capsule: A double-walled epithelial cup-shaped structure surrounding the glomerulus.
    • Visceral layer: Modified simple squamous epithelium (podocytes).
    • Parietal layer: Simple squamous epithelium.

Filtration Barrier

• The filtration barrier separates blood within glomerular capillaries from the urinary space of Bowman's capsule.
• Components:
  • Fenestrated endothelial capillaries
  • Thick continuous basement membrane
  • Filtration slits covered with diaphragms

Mesangial Cells

• Stellate-shaped cells located among glomerular capillaries.
• Functions:
  • Structural support
  • Phagocytic function

Juxtaglomerular Apparatus

• Located at the vascular pole of the renal corpuscle.
• Components:
  • Macula densa: Part of the distal convoluted tubule (DCT) facing the glomerulus. Acts as osmoreceptors sensitive to Na+ concentration.
  • Juxtaglomerular (JG) cells: Renin-producing cells in the wall of the afferent arteriole, respond to changes in blood pressure and Na+ levels.
  • Lacis cells (extraglomerular mesangial cells): Small, pale cells with pale nuclei.

Proximal Convoluted Tubule (PCT)

• Lined by simple cuboidal epithelium.
• Tubule cells have microvilli (brush border) on their luminal surfaces.
• Function:
  • Active reabsorption of glucose and amino acids
  • Reabsorption of Na+, Cl−, K+, and water (H₂O)

Distal Convoluted Tubule (DCT)

• Wide lumen, lined with cuboidal cells.
• Lacks a brush border.
• Function:
  • Reabsorption of Na+, K+, and water under the influence of aldosterone and ADH.
  • Excretion of H₂O and NH₃.

Urinary Passages

• Calyces
• Pelvis
• Ureter
• Bladder
• Urethra

Layers of Urinary Passage

• Mucosa: Transitional epithelium (urothelium)
• Muscular layer: Smooth muscle fibers (detrusor muscle)
• Adventitia: Loose connective tissue