Renal (Urinary) System

1. Renal (Urinary) System Chapter 17

2. Function Maintains homeostasis in ECF • Removing metabolic waste (except CO2) • e.g. ammonia, urea, uric acid • Removing foreign compounds • e.g. drugs, food additives, pesticides • Regulating salt concentrations, fluid volume, and pH

3. Anatomy • Kidneys (2) • process plasma into urine • Ureters (2) • tubes that carry urine to bladder • Urinary bladder • storage of urine • Urethra • carries urine to exterior Fig 17.1

4. Anatomy • Cortex • outer granular region • Medulla • inner striated region • renal pyramids • Renal Pelvis • central collecting cavity • Renal artery andvein Fig 17.2

5. Anatomy • Nephron • 1 million per kidney • functional unit of the kidney • smallest unit capable of forming urine Fig 17.2

6. Nephron Vascular Component • conducts blood • Renal Artery • Afferent Arteriole • Glomerulus • Efferent Arteriole • Peritubular Capillaries • Venules • Renal Vein Fig 17.5

7. Nephron Tubular Component • forms urine • Bowman’s capsule • Proximal Convoluted Tubule • Loop of Henle • Distal Convoluted Tubule • Collecting duct Fig 17.5

8. Urine Formation • Urine - water and waste solutes • Nephrons conduct three processes to convert blood plasma into urine • filtration • filter blood plasma to retain cells/proteins • reabsorption • remove valuable materials from filtrate • secretion • transfer additional wastes to filtrate

9. Filtration • Occurs in the glomerulus • Fenestrated capillaries • 3 layers of podocytes form capillary walls • Small pores (fenestrae) • filters plasma • proteins + cells stay in blood • forms ultrafiltrate Figs 17.8-17.10

10. Filtration • Filtration driven by blood pressure • Glomerular filtration is non-selective • Small particles pass (glucose, Na+, urea, H2O) • Large ones do not • 20% of plasma enters tubule • plasma filtered 65x/day Fig 17.10

11. Reabsorption • Occurs in remainder of nephron tubule • Selective movement of substances from tubule into plasma • Return of valuable substances to peritubular caps • Active or passive • Passive (no energy) • Active transport (requires energy) Fig 17.12

12. Secretion • Also occurs intubules • Additional materials transported from plasma in peritubular capillaries into tubule • excess K+, Ca2+ and H+, uric acid • foreign compounds • By passive diffusion or active carrier transport Fig 17.21

13. Proximal Tubule Proximal Tubule Reabsorbs: • 2/3 of plasma Na+ • 2/3 of plasma Cl- • 2/3 of plasma H2O • 100 % of plasma glucose Figs 17.2, 17.5

14. Active Transport in theProximal Tubule • Na+ actively transported from cell to blood • Creates Na+ gradient favoring Na+ flow from lumen • Na+ gradient used to transport glucose against concentration gradient (cotransport) • Glucose diffuses into blood passively Fig 17.13

15. Passive Reabsorption in theProximal Tubule • Cl- to be reabsorbed passively along electrical gradient • Water reabsorbed along osmotic gradient Fig 17.14

16. Acid Base Balance • Proximal tubule also secretes H+ and absorbs HCO3- • used to regulate pH • with  pH,  H+ secretion and HCO3- reabsorption Fig 17.28

17. Loop of Henle • Kidneys produce a hyperosmotic urine • less H2O than blood plasma • concentrating mechanism occurs in the Loop of Henle Fig 17.16

18. Loop of Henle • Countercurrent Multiplication • generates osmotic gradient that draws H2O out of the tubules to be reabsorbed • due to active reabsorption of Na+ & Cl- Exchange = 30 Exchange = 50

19. Loop of Henle • descending limb • permeable to water • no active transport • ascending limb • impermeable to water • lined w/ Na+-K+ pumps Fig 17.16

20. Loop of Henle • Pumping of ions out of ascending limb creates osmotic gradient • Water flows out of descending limb • Absorbed by peritubular capillaries • Fluid becomes more concentrated as it passes down descending limb Figs 17.16, 17.17

21. Loop of Henle • Removal of ions without water causes fluid to become less concentrated in the ascending limb • Less concentrated than blood in distal convoluted tubule • 25% of initial Na+ and water reabsorbed by loop of Henle Fig 17.16

22. Distal Convoluted Tubule and Collecting Duct • Secretion of K+ and H+ • Reabsorption of Na+ and water • Generation of hyperosmotic urine • final ~8% of water and Na+ reabsorbed Figs 17.19, 17.27

23. Hormonal Regulation of Reabsorption • Aldosterone • increases Na+ reabsorption and K+ secretion by distal & collecting tubules •  salt retention and BP (H2O retention) • ADH • induces implantation of aquaporins (water channels) into tubule cell membranes •  permeability of Distal and Collecting tubules to water •  H2O reabsorption =  urine volume

24. Triggering of Aldosterone Release • release induced by juxtaglomerular apparatus • region of afferent arteriole that comes into contact w/ascending limb of Loop of Henle • releases renin (enzyme) into blood in response to BP • renin converts angiotensinogenangiotensin I Fig 17.26

25. Triggering of Aldosterone Release • angiotensin I converted to angiotensin II (fully activated) by angiotensin converting enzyme in lungs • angiotensin II stimulates aldosterone release Fig 17.26

26. Urination • Ureters • transfer urine to pelvic region • Urinary Bladder • Stores urine • smooth muscle, stretchable walls • Two sphincters • internal urethral sphincter (involuntary) • external urethral sphincter(voluntary) Fig 17.1

27. Urination Urination Reflex: • Stretch receptors in bladder wall  spinal cord • efferents to smooth muscle  contraction • Internal sphincter relaxes • External sphincter relaxes Fig 17.1