Urinary System Kidney Structure kidneys, ureters, bladder & urethra Capsule Kidney Function Hilum Filters blood • ureter → renal pelvis • removes waste products → major and minor calyxes • conserves salts, glucose, • renal artery and vein proteins, nutrients and water → segmental arteries → interlobar arteries Produces urine → arcuate arteries → interlobular arteries Endocrine functions • regulates blood pressure Medulla • produces • renal pyramids • renin • cortical/renal columns • erythropoietin • prostaglandins Cortex • converts vitamin D to active form • renal corpuscles • cortical labryinth of tubules • medullary rays Renal Lobe Renal Lobule Uriniferous Tubule = renal pyramid & overlying cortex = medullary ray & surrounding cortical labryinth Nephron + Collecting tubule Cortex Nephron Renal corpuscle produces glomerular ultrafiltrate (180 L per day) from blood Ultrafiltrate is concentrated • Proximal tubule • convoluted • straight • Henle’s loop Medulla • thick descending • thin • thick ascending • Distal tubule • Collecting tubule Papilla Calyx Urine (1-2 L per day) secreted from collecting ducts into calyxes 1 Renal Cortex Renal Cortex Medullary ray = collecting tubules Renal corpuscle = glomerulus + Bowman’s capsule Cortical labyrinth of tubules Sobotta & Hammersen: Histology Juxtaglomerular apparatus Renal Corpuscle • macula densa in distal tubule • JG cells in afferent arteriole • extraglomerular mesangial cells Urinary / Bowman’s space parietal Bowman’s layer capsule visceral layer Glomerulus Glomerulus • fenestrated capillaries • podocytes • intraglomerular mesangial cells 2 Renal Corpuscle Intraglomerular Mesangial Cells • Support capillaries • Phagocytose basal lamina Vascular pole • Vasoconstrict in response to angiotensin II Urinary pole Sobotta & Hammersen: Histology • Endothelial cell • 70-90 nm fenestra restrict proteins > 70kd Podocytes • Basal lamina Urinary Filtration • heparan sulfate is negatively charged • produced by endothelial cells & podocytes Membrane • phagocytosed by mesangial cells • Podocytes • pedicels 20-40 nm apart • diaphragm 6 nm thick with 3-5 nm slits • podocalyxin in glycocalyx is negatively charged Urinary Membrane 3 Juxtaglomerular Apparatus Macula densa in distal tubule • monitor Na+ content and volume in DT • low Na+: • stimulates JG cells to secrete renin • stimulates JG cells to dilate afferent arteriole Proximal tubule • tall, narrow columnar cells • proximal convoluted tubule • numerous microvilli • thick descending limb Henle’s loop JG cells Henle’s loop • secrete renin into circulation • thin descending & ascending limbs • renin converts angiotensinogen → angiotensin I • contain angiotensin converting enzyme (ACE) Distal tubule • lung is principal site of ACE activity • thick ascending limb Henle’s loop • ACE converts angiotensin I → II • distal convoluted tubule • contain angiotensin I & II • macula densa in DCT • angiotensin II constricts vasculature and stimulates secretion of aldosterone and ADH Collecting tubule & duct Mesangial • primarily in afferent arteriole cell • specialized smooth muscle cells • no basal lamina between JG cells & macula densa JG cell Macula Extraglomerular mesangial cells densa • also known as Polkissen or lacis cells Proximal Convoluted Tubule Henle’s Loop (thin segments) • Cuboidal (low to high) cells • Eosinophilic granular cytoplasm • Squamous cells • Basal nuclei • slightly thicker than endothelial cells • Elaborate brush/striated border • Few short microvilli • Lateral interdigitations • Lateral interdigitations • Descending limb • highly permeable to water, salt and urea • Resorbs 100% protein, amino acids, glucose, • Ascending limb creatinine, and bicarbonate ions • impermeable to water • permeable to salt which enters interstitium • Resorbs 70-80% of Na+, Cl-, and water • Na+/K+ pumps in basolateral membrane • Na+ pumped into interstitium • Cl- and water follow • Secretes waste products into lumen 4 Distal Tubule (DCT & thick ascending limb of Henle’s loop) Renal Medulla • Low cuboidal cells • Collecting tubules/ducts • Clear pale cytoplasm • Apical nuclei (DCT) • Henle’s loop (thin segments) • Central nuclei (Henle’s loop) • Capillaries of vasa recta • Numerous mitochondria • Absent (or few short) microvilli • Basal interdigitations • Numerous zonula occludens • Not permeable to water or urea Sobotta & Hammersen: Histology • Active Na+/K+ pumps (DCT) • aldosterone stimulates salt resorption • H+ and K+ transported into lumen • Active Cl- pumps (Henle’s thick) • Cl- enters interstitium (Na+ follows) Gartner & Hiatt: Color Textbook of Histology Collecting Tubule & Duct Renal Cortex Proximal tubule Distal Proximal tubule Henle’s loop • Cuboidal to columnar cells (convoluted) tubule (straight) (thick) • Clear cytoplasm • Central nuclei • Permeable to urea • In response to ADH, becomes permeable to water which enter the interstitium Collecting tubule Sobotta & Hammersen: Histology 5 Formation of Urine Countercurrent Multiplier System Increasing osmolarity gradient exists from corticomedullary junction to deep in medulla ** due to high urea and salt content deep in medulla •Descending thin limb of Henle is freely permeable to water and salt • Due to increasing osmolarity of interstitium: lumenal volume decreases and osmolarity increases • Ascending (thin and thick) limb of Henle and DCT are not permeable to water • Lumenal volume does not change • Urea enters lumen • Cl- pumped into interstitium (Na+ follows) → increases salt deep in medulla → ultrafiltrate becomes hypotonic as it ascends • Without ADH: collecting tubule/duct impermeable to water • ADH (pars nervosa of pituitary) makes collecting tubule/duct freely permeable to water and urea → increases water resorption, decreases urine volume, and increases urine tonicity → increases urea content deep in medulla to maintain interstitial osmolarity gradient Angiotensin II Regulation of Blood Pressure Angiotensin II Regulation of Blood Pressure Burns & Cave: Histology & Cell Biology 6 Additional Regulators of Kidney Function Atrial Natriuretic Peptide (ANP) Vasa Rectae • Secreted by atrial cardiac myocytes • Function • Peritubular capillary system in medulla • decreases renin release • Freely permeable to water and salts • decreases aldosterone release • Counter current exchange system: • blocks resorption salt and water equilibrates contents of medullary • decreases blood pressure interstitium and vasculature Alcohol • decreases ADH release Caffeine • increases salt resorption in DCT Vasculature of Kidney Renal Segmental Interlobar Arcuate Interlobular artery artery artery artery artery Urine is excreted through Afferent glomerular arteriole • Calyxes and renal pelvis Cortex Glomerular capillaries • Ureters Peritubular • Urinary bladder (storage) Interlobular Stellate capillary Efferent glomerular vein vein arteriole network Cortical • Urethra nephrons Juxtamedullary & deep cortical nephrons Arcuate vein Vasa rectae Medulla Interlobar vein Renal vein Netter: Atlas of Human Anatomy 7 Ureter Urinary Bladder • Mucosa - transitional epithelium • Muscosa - transitional epithelium • provides osmotic barrier • Lamina propria • Lamina propria • Muscularis – smooth muscle • Muscularis – smooth muscle • Inner longitudinal • inner longitudinal • Middle circular Empty • middle circular • Outer longitudinal (lower 1/3) (internal urethral sphincter) • outer longitudinal Sobotta & Hammersen: Histology Sobotta & Hammersen: Histology Gartner & Hiatt: Color Textbook of Histology Urethra • Mucosa • varies from transitional to stratified columnar to pseudostratified columnar to stratified squamous in different regions • Lamina propria • contains glands of Littre • highly vascularized • External urethral sphincter of skeletal muscle • In the male, 3 regions: • prostatic • membranous • penile or spongy 8.