1. EXCRETORY SYSTEM - HISTOLOGY
Dr. ANAND SRINIVASAN

2. At the end of the lecture students shall be able to :
Identify the key features and slides of kidney, ureter, urinary bladder and urethra.

3. EXCRETORY SYSTEM
Composed of
Kidneys
Ureters
Urinary bladder
Urethra

4. Know the following macroscopic features :
Renal sinus
Renal cortex & medulla
Renal pyramid
Renal papillae
Ducts of Bellini
Medullary rays
Renal column of Bertin

5. With your knowledge in gross anatomy, identify the labels
1 – 11.
Medullary rays
Juxtaglomerulus
Glomerulus
Arcuate vessels
Afferent arterioles
Vasa recta
Interlobular vessels
Minor calyx
Major calyx
Renal papillae
Renal columns of Bertin

6. KIDNEY – MICROSCOPIC Composed many renal (uriniferous) tubules made of
Nephron
Collecting tubule
NEPHRON
Structural and functional unit
1 – 4 million in each kidney
Cortical nephrons & Juxtamedullary nephrons
Made of
Renal corpuscle
Proximal & Distal convoluted tubule
Loop of Henle

7. Renal corpuscle Made of 2 components BOWMAN’s CAPSULE Bowman’s capsule
Glomerulus
BOWMAN’s CAPSULE
Blind end of the nephron
Parietal layer – simple squamous epithelium continuous with PCT at urinary pole.
Visceral layer – specialized epithelium (Podocytes) continuous with parietal layer at vascular pole
Bowman’s space – between parietal & visceral layers

9. GLOMERULUS PODOCYTES GLOMERULAR FILTER
Afferent arteriole more diameter than efferent
Glomerular capillaries lined by fenestrated endothelium
Supported by mesangial cells
PODOCYTES
Primary and secondary (pedicels)foot processes
GLOMERULAR FILTER
Fenestrated endothelium of capillaries
Glomerular basement membrane
Filtration slits between pedicels of podocytes

10. PROXIMAL CONVOLUTED TUBULE
Simple cuboidal epithelium with microvilli
LOOP OF HENLE
Thick segment – simple cuboidal epithelium
Thin segment – simple squamous epithelium
DISTAL CONVOLUTED TUBULE
Simple cuboidal epithelium (no brush border)
COLLECTING TUBULES
Simple cuboidal epithelium with pale cytoplasm
COLLECTING DUCT
Simple columnar epithelium with pale cytoplasm

11. JUXTAGLOMERULAR APPARATUS
JUXTAGLOMERULAR (JG) CELLS
Modified smooth cells of tunica media of afferent arteriole at the point of contact with DCT
Sensitive to blood pressure in afferent arteriole.
Secretes – Renin
MACULA DENSA
Specialized region in DCT sensitive to Na+
LACIS / POLKISSEN CELLS
Extraglomerular mesangial cells; ? Erythropoietin

13. URETER – Histological features
MUCOSA
Transitional epithelium
Lamina propria rich in elastic fibers
Mucosa thrown into star shaped lumen
MUSCLE COAT
2 layers in the upper 2/3 and 3 in the lower 1/3
Inner longitudinal, outer (middle) circular
ADVENTITIA
Outermost coat made of loose connective tissue

15. URINARY BLADDER MUCOSA MUSCLE COAT ADVENTITIA / SEROSA
Transitional epithelium with lamina propria
Superficial cells flattened when bladder is full
MUSCLE COAT
Inner longitudinal, middle circular and outer longitudinal
ADVENTITIA / SEROSA
Fibroelastic connective tissue ± Peritoneum

17. MALE URETHRA Divided into Prostatic – transitional epithelium
Membranous – (Pseudo)stratified columnar
Penile – (Pseudo)stratified columnar
Fossa navicularis – stratified squamous

19. FEMALE URETHRA
4 cms
Lined by stratified squamous epithelium except near the bladder where it is lined by transitional epithelium
Urethral (Skene’s) glands open into urethra
Inner longitudinal and outer circular muscle layers

21. RECOMMENDED READING Cell biology & Histology – BRS Review
Microanatomy workbook – RAKMHSU
Di Fiore’s Histology