L17: Histology Of Urinary System Flashcards
Main functions of urinary system
- Production, passage, storage and voiding of urine (toxic metabolites: nitrogen-containing product of protein breakdown —> urea + creatinine)
- Water
- Electrolyte
- Acid-base
Uriniferous tubule components
- Nephron
- Renal corpuscle (Bowman’s capsule + glomerulus)
- Proximal convoluted tubule
- Loop of Henle
- Distal convoluted tubule - Collecting duct
Formation of urine
- Filtration
- Secretion
- Reabsorption
***2 types of nephrons
- Cortical nephrons (80%)
- renal corpuscle: outer cortex
- LoH: short, outer medulla
- efferent arteriole: peritubular capillary network, surrounding convoluted tubule
- medullary ray: collecting tubules - Juxtamedullary nephrons (20%)
- renal corpuscle: juxtamedullary cortex
- LoH: long, medulla
- efferent arteriole: Vasa recta (vascular loop), surrounding collecting ducts + LoH
***Renal circulation
Aorta —> Renal artery —> Segmental —> Interlobar —> Arcuate —> Interlobular artery —>
afferent arteriole —> glomerulus (glomerular tuft: 20-40 loops of fenestrated capillary) —> efferent arteriole —> peritubular capillaries / vasa recta —>
Interlobular vein —> Arcuate —> Interlobar —> Renal vein —> IVC
Structure of Bowman’s capsule
- Basement membrane
- Parietal epithelium
- Visceral epithelium (Podocytes)
Glomerulus inserted into Bowman’s capsule (fist in balloon)
Glomerular filtration barrier
Fenestrated endothelium —> BM of glomerulus —> BM of Bowman’s capsule —> Visceral epithelium (Podocytes) filtration slit
(Podocytes processes interdigitate with other podocytes’ processes —> together wrap around glomerular capillary)
Proximal convoluted tubule
Structure:
Cuboidal (Apical tight junctions, interdigiting) + microvilli
Function: Reabsorption of: 70% water + ALL organic nutrients
- Water
- Amino acids / Proteins
- Glucose / Carbohydrates
Loop of Henle
Structure:
Simple squamous + small number of microvilli
Function:
Creation of hypertonicity between collecting duct and interstitium —> allow water to diffuse easily
Distal convoluted tubule
Structure:
Cuboidal (cell junction impermeable to water) + sparse microvilli
Function: ***Acid-base + Water homeostasis: Reabsorption + Secretion
- Reabsorption of: (Active symport system)
1. Water
2. Na
3. HCO3- - Excretion of:
1. K
2. H+
Collecting duct
Structure:
Cuboidal: Principal cells (light) + Intercalated cells (dark)
- Principal cells (light) —> cilium: Mechanosensor of fluid flow and contents
- Intercalated cells (dark) —> Acid-base transport, water-impermeable
Function:
- Reabsorption of water under ADH influence
Juxtaglomerular apparatus
- Juxtaglomerular cells (Baroreceptor detect BP in afferent arteriole —> renin)
- Macula densa (Chemoreceptor detecting ↓ GFR —> ↓ [Na] —> JG cell —> renin)
- Mesangial matrix cell (anchoring glomerular capillary)
Interstitial cells
Function:
Production of erythropoietin + Maintenance of renal architecture
Transitional epithelium / Urothelium
Expandable epithelium:
Non-distended state / contracted state:
- Cuboidal base layer
- Polygonal middle layer
- Columnar surface layer (convex surface bulging into lumen)
Distended state: Squamous
Microstructure of ureter
- Transitional epithelium (expandable)
- Lamina propria (dense collagenous and elastic)
- Muscle layer (Inner longitudinal + outer circular, lower 1/3 of ureter: extra outermost longitudinal)
—> Peristaltic smooth muscle contraction, forcing urine down bladder in one direction - Adventitia (loose CT + ANS plexus + blood vessel + lymphatics)
