Urinary system Histology Khaleel Alyahya khaleelya@gmail.com

Urinary System Kidney Ureters Urinary Bladder Urethra

Functions Maintain the purity & constancy of internal fluids. Regulate blood volume. Produce rennin to help regulate blood pressure. Produce erythropoietin (hormone) to stimulate RBC production. Produce urine.

Structure of the Kidneys Kidney is divided into: Renal Cortex (outer region) Renal Medulla (inner region) Cortex Dark brown and granular Medulla 6-12 pyramid-shape regions (renal pyramids, NO nephrons) The base of pyramid is toward the cortex (corticomedullary border) The apex (renal papilla) toward the hilum that perforated by 12 openings of the ducts of Bellini. The apex is surrounded by minor calyx. 5 or 8 minor calyces join to form 3 or 4 major calyces that form renal pelvis. Pyramids are separated by cortical columns of Bertin

The Kidneys

Cortical Arch Renal corpuscles Convoluted tubules Medullary rays (cortical continuation of pyramids)

Uriniferous Tubule Is the functional unit of the kidney. Is formed of: 1- Nephron 2-Collecting tubule (duct) They are densely packed. They are separated by thin stroma and basal lamina Corpuscles Convoluted tubules (cortical labyrinth) Medullary rays (cortical continuation of pyramids)

Nephron There are 2 types: Nephron is formed of: Cortical nephrons Juxtamedullary nephrons Nephron is formed of: Renal corpuscle (cortical & juxtamedullary). Proximal tubule. Henle’s loop. Distal tubule Note: Collecting tubule (duct) is NOT a part of the nephron!

Uriniferous Tubule

Uriniferous Tubule

Renal Corpuscle Two poles: Glomerulus Bowman’s capsule Mesangial cells vascular urinary Glomerulus Bowman’s capsule parietal layer urinary or glomerular space visceral layer or podocytes Mesangial cells intraglomerular extraglomerular

Renal Corpuscle Renal cortex Renal corpuscle

Renal Corpuscle

Renal Corpuscle

Renal Corpuscle

Renal Corpuscle

Renal Corpuscle

Filtration Barrier Endothelial wall of the capillaries Basal lamina Visceral layer of Bowman’s capsule (podocytes) Podocytes have primary (major) processes and secondary (minor) processes (pedicles). Between pedicles (on the surface of capillaries) there are filtration slits that have slit diaphragm

Filtration Barrier

Proximal Tubule It has 2 regions: Pars convoluta proximal convoluted tubule Pars recta descending thick limb of Henle’s loop It is composed of simple cuboidal epithilum with acidophilic cytoplasm. The cells have striated or brush border and lateral interdigitations. They have well-defined basal lamina. Proximal tubules are long and highly convoluted so most of cortical tubular sections are proximal tubules.

Proximal Tubule Cell of proximal tubule

Thin limb of Henle’s Loop It has 3 regions: Descending thin limb Henle’s loop Ascending thin limb Note: It is longer in juxtamedullary nephron than in cortical nephron It is composed of simple squamous epithelium

Renal Medulla

Distal Tubule It has 3 regions: Ascending thick limb of Henle’s loop low cuboidal epithelium Macula densa 1st part, tall & narrow cells Pars convoluta distal convoluted tubule formed of low cuboidal epithelium Distal tubules drain into collecting tubules Aldosterone hormone increase the active reabsorbtion of sodium from the lumen of tubule into interstitium

Distal Tubule Cell of distal tubule

Juxtaglomerular Apparatus It has 3 components: The macula densa of distal tubule Juxtaglomerular cells of afferent glomerular arteriole modified smooth muscle of tunica media they secrete renin, angiotensin-converting enzyme and angiotensin The extraglomerular mesangial cells

Juxtaglomerular Apparatus

Juxtaglomerular Apparatus

Collecting Tubules Are composed of simple cuboidal epithelium They aren’t part of nephron They have 3 regions: Cortical Medullary Papillary They are formed of: principle cells intercalated cells They are impermeable to water except in presence of antidiuretic hormone.

Collecting Tubules Cell of collecting tubule

Renal Interstitium It is a very flimsy, scant amount of CT contains. Fibroblasts. Macrophages. Interstitial cells their nuclei are elongated and they contain lipid droplets they secrete medullipin I, which is converted in the liver into medullipin II, that lowers blood pressure

The Ureters Mucosa is formed of transitional epith. and lamina propria. Muscularis (muscular coat) is formed of 2 layers of smooth muscle: inner longitudinal outer circular Adventitia (fibrous CT covering)

The Ureters

The Urinary Bladder It has the same structure as the ureter EXCEPT: The dome-shaped cells of transitional epithelium have plaques (rigid, thickened regions of plasmalemma) It has 3 layers of smooth muscle, inner and outer longitudinal and middle circular Its outer covering is serosa

The Urinary Bladder

That’s all folks! Questions?