The Urinary System Ch 24 Human Anatomy Sonya Schuh-Huerta, Ph.D.

1. The Urinary System Ch 24 Human Anatomy Sonya Schuh-Huerta, Ph.D. C. Babaian

2. Outline • Historical perspective • Kidney overview • Nephron structure & function • Ureters, Bladder & Urethra • Hot research • Disorders/diseases

3. Organs of the Urinary System • Kidneys • Ureters • Urinary bladder • Urethra

4. L. Da Vinci, 1508 Why study the kidney?What does it do?

5. The kidney: a vital organ with many functions • Filters the blood -Removal of wastes & toxins -Waste products: urea, uric acid, creatinine -Production of urine • Homeostasis -Body fluids & pressure -Ions (Na+, K+, Cl-, Ca2+, HCO3-) -Acid-base balance -Blood sugar • Production of hormones -Blood volume & pressure -Calcium metabolism -Red blood cell production Kidney Ureter Bladder

6. What can urine tell us? • Historical interest in resolving urine’s • composition & relation to health • Alchemists of Medieval Europe • thought urine contained gold! • Urea isolated in 1773; 1st organic • compound to be artificially synthesized Gerrit Dou, 1617 Urine color wheel

7. What can urine tell us? • Yellow color: breakdown products of • hemoglobin Modern-day urine color wheel Urine color & components tell a lot about a person’s health

8. Salt & water balance • Huge variation in amount & concentration of urine • Kidney’s job: keep salt & water balanced (input = output) • Maintain osmolarity of ~300 mOsmol/L Matt Stonie, competitive eater

9. Renal artery Renal hilum Renal vein Kidney Ureter Urinary bladder Urethra The kidneys

10. Location & gross anatomy • In almost all animals including humans • Paired, “kidney” bean-shaped organs • Located in the abdominal cavity: T12 – L3 • Within the retroperitoneum • Left kidney behind spleen • Top of right kidney behind liver • Hilum opening where renal artery, vein, & ureter join kidney • Surrounded by fibrous capsule, fat & fascia Dorsal view

11. Position of the kidneys Anterior Inferior vena cava Aorta Peritoneal cavity (organs removed) Peritoneum Supportive tissue layers Renal vein Renal fascia anterior posterior Renal artery Perirenal fat capsule Fibrous capsule Body of vertebra L2 Body wall Posterior 12th rib

12. Gross anatomy of the kidney Renal cortex Renal medulla Major calyx Papilla of pyramid Renal pelvis Minor calyx Ureter Renal pyramid in renal medulla Renal column Fibrous capsule

13. Gross anatomy of the kidney renal capsule medulla renal pelvis hilum

14. Blood vessels of the kidney Cortical radiate vein Cortical radiate artery Arcuate vein Arcuate artery Interlobar vein Interlobar artery Segmental arteries Renal vein Renal artery Renal pelvis Ureter Renal medulla Renal cortex (a) Frontal section, posterior view, illustrating major blood vessels

15. Blood vessels of the kidney Aorta Inferior vena cava Renal artery Renal vein Segmental artery Interlobar vein Interlobar artery Arcuate vein Arcuate artery Cortical radiate vein Peritubular capillaries and vasa recta Cortical radiate artery Afferent arteriole Efferent arteriole Glomerulus (capillaries) Nephron-associated blood vessels (see Figure 24.9) (b) Path of blood flow through renal blood vessels

16. The kidney • Contains ~1 million tubular • structures = nephrons • Carry out functions of the • kidney

17. At the microscopic level

18. Nephron – the functional unit • Glomerulus & Bowman’s capsule • Proximal tubule • Loop of Henle • Peritubular capilaries & • Vasa recta • Distal tubule • Collecting duct

19. cortex Edward Sales

20. First part of the nephron • Renal corpuscle  Bowman’s capsule + glomerulus • Glomerulus= tuft of porous capillaries • Bowman’scapsule = surrounds glomerulus Glomerulus Glomerulus Madelaine Dela Cruz

21. Glomerular filtration • Holds back proteins & RBCs • Allows small molecules through: • Water • Ions (Na+, Cl-, K+, • Ca2+, HCO3-) • Glucose • Amino acids • Urea & uric acid Glomerular capsular space Efferent arteriole Afferent arteriole Proximal convoluted tubule Glomerular capillary covered by podocytes Outer layer of Bowman’s capsule

22. Glomerular filtration • Glomeruli • Porous capillaries • Fed & drained by afferent & efferent arterioles • Efferent arteriole has smaller diameter • Filter 1 liter of fluid every 8 minutes! • 180 liters of fluid per day • Total blood volume is filtered ~60X/day!

23. Cytoplasmic extensions of podocytes Filtration slits Podocyte cell body Fenestrations (pores) Glomerular capillary endothelium Foot processes of podocyte Filtration membrane • Filter between blood in glomerulus & space of Bowman’s capsule 1. Endothelium of capillary 2. Basement membrane 3. Slits between foot processes of podocytes

24. How does the nephron work? • 1) Filtration • Blood filtrate leaves glomeruli • 2) Reabsorption • Nutrients (glucose), H2O, & • essential ions taken back into blood • 3) Secretion • Active process of removing undesirable chemicals from blood • Dumping them into tubules Afferent arteriole Glomerulus Efferent arteriole Bowman’s capsule Renal tubule Peritubular capillary Filtration • 4) Excretion • Filtrate leaves as urine Reabsorption Secretion Urine

25. Different cell types & functions Renal cortex Renal medulla Glomerular capsule: parietal layer Renal pelvis Basement membrane Ureter Kidney Podocyte Fenestrated endothelium of the glomerulus Renal corpuscle Glomerular capsule Glomerulus Glomerular capsule: visceral layer Distal convoluted tubule Microvilli Mitochondria Proximal convoluted tubule Highly infolded plasma membrane Proximal convoluted tubule cells Cortex Medulla Thick segment Distal convoluted tubule cells Thin segment Loop of Henle Descending limb Ascending limb Nephron loop (thin-segment) cells Collecting duct Principal cell Intercalated cell Collecting duct cells

26. Glomerular Filtration Rate • Glomerular Filtration Rate (= GFR) • Volume of fluid filtered by the glomeruli per unit time  180 L/day or 125 ml/min • Can only be measured by compounds that are not reabsorbed or secreted

27. Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ K+ ATP K+ Coupling of water reabsorption to Na+ reabsorption Tubule Cell Lumen Peritubular Capillary low Na+ NaK ATPase

29. Proximal convoluted tubule • Most solutes are reabsorbed here • All glucose is reabsorbed • Drugs/toxins are secreted • Filtrate is isoosmotic

31. Loop of Henle • Ascending limb permeable to Na+, not H2O • Descending limb permeable to H2O, not Na+ • Concentrates medulla • Part of urine-concentrating system •  Countercurrent multiplier system Friedrich Henle, 1873

32. Countercurrent Multiplier System • Fluids in adjacent tubes running in opposite directions – promotes the exchange of material • Build-up of concentration • Movement of solutes • Examples in nature & mimicked in industry • Loop of Henle!

33. Loop of Henle Juxtamedullary nephron Cortical nephron • Cortical nephrons • Juxtamedullary nephrons • Loop of Henle plunges deep into medulla • Vasa recta • Set up the concentration gradient of medulla • Create driving force for maximal H2O reabsorption from collecting ducts Efferent arteriole Cortex Afferent arteriole Efferent arteriole Peritubular capillaries Corticomedullary junction Vasa recta Collecting duct Medulla high osmolarity

34. The kidney cortex & medulla cortex medulla Benjamin Yates Edward Sales

35. Blood vessels of nephrons • Peritubular capillaries • Capillary network of cortical nephrons • Adapted for absorption • Low-pressure, porous capillaries • Vasa recta • Capillary network of juxtamedullary nephrons • Thin-walled looping vessels • Descend deep into the medulla • Part of the kidney’s urine-concentrating mechanism

36. Adaptations of the kidney • Desert animals  conserve H2O • Many long Loops of Henle • Highly concentrated urine (uric acid) • Urine “pellet” medulla Benjamin Yates Kangaroo rat

38. Distal convoluted tubule • Permeable to (actively pumps) Na+ out of tubule • Impermeable to H2O • Filtrate hypoosmotic

40. Collecting duct • Reabsorption of Na+ under hormonal control • –Aldosterone (from adrenal gland) • Reabsorption of H2O under hormonal control • –Antidiuretic hormone, ADH (from posterior pituitary) • The nephrons fine-tune the final concentration of urine based on body’s needs

41. How does the nephron fine tunethe reabsorption of Na+and water?

42. Juxtaglomerular Apparatus • Regulates salt & fluid balance • Special cells: granular cells & the macula densa Red blood cell Efferent arteriole Proximal tubule Macula densa cells of the ascending limb Lumens of glomerular capillaries Extraglomerular mesangial cells Granular cells Afferent arteriole Mesangial cells between capillaries Juxtaglomerular apparatus

43. Juxtaglomerular Apparatus • Granular cells  Modified smooth muscle cells of aff. arteriole • Make renin • Macula densa  Cells of distal ascending limb • Monitors solute concentration (Na+) • When BP is low (GFR low)  Na+ low  signals granular cells to secrete renin • Renin-Angiotensin System (RAS)  • Regulates sodium & fluid balance (& BP)

44. Plasma Volume / Blood Pressure Macula densa Vascular & atrial pressure GFR / Flow / NaCl Posterior pituitary Granular cells Antidiuretic hormone Renin Collecting ducts from Liver Aquaporin channels H2O Reabsorption Angiotensin II Adrenal gland Aldosterone Collecting ducts Excretion of salt & H2O Fluid Volume / BP Sodium Reabsorption

46. Renin-Angiotensin System • Many drugs interrupt steps of this system • Used to treat high BP (hypertension), congenital • heart disease, kidney disease, etc.  diuretics • Caffeine & alcohol also diuretics

47. Rest of the urinary system: Ureters • Carry urine from the kidneys to the urinary bladder • Oblique entry into bladder prevents backflow of urine • Histology of ureter • Mucosa  transitional epithelium • Muscularis 2 layers • Inner longitudinal layer • Outer circular layer • Adventitia typical connective tissue

48. Transitional Epithelium – Review… • Description: • Has characteristics of stratified cuboidal & stratified squamous • Superficial cells dome-shaped when bladder is relaxed, squamous when full • Function: permits distension of urinary organs by urine • Location: epithelium of urinary bladder, ureters, proximal urethra

49. Transitional Epithelium (h) Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamous-like, depending on degree of organ stretch. Transitional epithelium Function: Stretches readily and permits distension of urinary organ by contained urine. Basement membrane Location: Lines the ureters, bladder, and part of the urethra. Connective tissue Photomicrograph: Transitional epithelium lining the bladder, relaxed state (390); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine.

50. Histology of the ureter Lumen Adventitia Circular layer Muscularis Longitudinal layer Transitional epithelium Mucosa Lamina propria