Understanding the Urinary System: Functions and Physiology

1. The Urinary System Chapter 26

2. Functions figure 26.1 • ___________- • Excrete waste in urine • Regulate blood volume & composition (ions, pH) • Help regulate blood pressure • Synthesize glucose • Release erythropoietin • Participate in vitamin D synthesis • ___________ – transport urine from kidneys to urinary bladder • Urinary bladder– stores urine, capacity≈ 700-800mL • ____________ – discharges urine from the body

6. Kidney • Regulates ___________________ composition • Na+, K+, Ca2+ , Cl-, and HPO42- • Regulate _______________ • Excrete H+ • Conserve HCO3– • Reg. __________________ – conserve or elim water •  blood volume  bp,  blood vol   bp • Regulating ___________ • Secrete: renin   bp, or adjust blood volume • Maintaining blood osmolarity- reg water & solute loss • Hormones: calcitrol (active Vit D), ________________________ • Regulate blood glucose- use glutamine in gluconeogenesis • Excreting waste and foreign substances

7. Kidney anatomy figure 26.3 • Retroperitoneal • 3 layers surrounding • Renal capsule – deepest • Adipose capsule • Renal fascia – superficial, anchors to ab wall • _______________- fissure where following emerge: • Renal aretery • Renal vein • Ureter • Internally, 2 distinct regions: • Renal _________ – superficial • Renal _________ – deep, arranged in renal pyramids

11. Nephron figure 26.5 a & b • Functional unit of the kidney, 2 parts: • _________________ – where blood plasma is filtered • Glomerulus – capillary network • Glomerular (Bowman’s) capsule – epithelial cup • _________________ – into which the filtrate is passed • Proximal convoluted tubule (PCT) • Loop of Henle (LOH) • Distal convoluted tubule (DCT) • Types: • __________ nephron- short LOH, blood from peritubular cap • __________________ nephron- close to medulla, long LOH • Long loops enable excretion of very dilute or very [ ]

14. Renal corpuscle fig 26.6 • __________________- capillary network • Glomerular (Bowman’s) capsule- double walled epithelial cup that surrounds the capillaries • Blood plasma is filtered & collected in capsule • Filtered fluid then passes thru renal tubule • _____________- visceral, modified simple squamous cells, wrap around glomerular capillaries & form inner wall of capsule • Outer wall (parietal) is simple squamous

18. Renal physiology, 3 processes • _______________________ • Water & most solutes: capillary  renal capsule • _______________________ • Filtered fluid move thru tubule • Cells reabsorb 99% of water & useful solutes • Returns to blood via • Peritubular capillaries • Vasa recta • ________________________ • Removes substances from blood • Urine contains these excreted substances: wastes, drugs, excess ions

20. Glomerular filtration fig 26.8 • Filtration fraction- amt of plasma in ______________ that becomes glomerular filtrate = 16-20% of plasma • Daily volume of glomerular filtrate: • 150L female,180L male • >99% returned to blood,  1-2 L urine/day • Substances pass _________________: • Glomerular endothelial cells = fenestrated • Between capillaries mesangial cells – regulate GF • Basal lamina • Podocytes w/ pedicel create filtration slits • ____________ & ______________________ • Most plasma proteins, blood cells & platelets DO NOT

21. The filtration membrane, fig 26.8

22. Net filtration pressure, figure 26.9 • Glomerular filtration dependent on these 3: • Glomerular blood hydrostatic pressure • Blood pressure in glomerular capillaries • Promotes filtration • Capsular hydrostatic pressure • Hydrostatic P exert by fluid in capsular space • Opposes filtration • Blood colloid osmotic pressure • Presence of proteins in blood plasma • Opposes filtration

24. Glomerular filtration rate (GFR) • Filtrate formed in renal corpuscles of both kidneys each minute • 125 mL/min male, 105 mL/min female • Homeostasis req it to be ≈ constant • If too ↑, substance not reabsorbed, lost in urine • If too , not enough waste excreted • Directly related to P determining NFP • Regulation: • Adjusting _______________ to glomerulus • Alter glomerular capillary __________- filtration

25. Regulation of GFR, table 26.2 • 1. _____________________ • Myogenic mechanism- smooth muscle contraction – wall of afferent arteriole • ↑ bp, stretch wall,  smooth mus contracts, narrow lumen renal blood flow    GFR • Tubuloglomerular feedback- macula densa provide feedback to glomerulus • If GFR ↑ due to ↑ bp, filtered fluid flows faster, less time for reabsorption  nitric oxide not released & ________________ constricted

26. Regulation of GFR (2) • 2. _____ regulation- kidney bv supplied by SympNS • Release NE vasoconstrict (exercise, hemhorrrage) • Blood flow , GFR  •  urine output, conserve blood volume • ↑ blood flow to other body tissues • At rest, bv dilated & autoregulation occurring • 3. ___________ regulation- • Angiotensin II- GFR by vasoconstriction • Atrial natriuretic peptide (ANP) secreted when ↑ blood vol  relax mesangial cells ↑ SA  ↑ GFR

29. Tubular reabsorption • PCT • ______ & _______ reabsorbed in large quantities • ≈65% of filtered water reabsorbed • Na+/glucose (phosphate, sulfate, aa) symporters • Na+/H+ antiporter • _________ (HCO3-) reabsorbed- fac diffusion • _________ of water • Concentrates remaining solutes in PCT • Passive reabsorption of other solutes: • Cl-, K+, Ca2+, Mg2+, urea • Urea and ammonia ____________ by PCT

30. PCT

31. PCT

32. PCT, 2nd half

33. Tubular reabsorption (2) • Loop of Henle • Descending limb: • ___________ is reabsorbed (15% of filtered water) • Ascending limb: • Na+, K+, 2Cl- symporters • most K+ leaks back into tubule thru channels • Ca2+, HCO3-, • ____________- ascending LOH virtually impermeable to water • not automatically coupled to reabsorption of other solutes like in PCT • Filtrate osmolarity  as ascend (ions, not water reabsorb)

34. Ascending LOH

35. Tubular reabsorption (3) • DCT: • Na+ Cl- symporter  reabsorption • PTH causes reabsorption of Ca2+ • Water 10-15%, (at this point 80% already ab) • * by time fluid reaches end of DCT 90-95% of filtered solutes & water have been returned to bloodstream • Collecting duct: • ______ reabsorb thru leak channel Na+/K+pumpblood • ______ reabsorbed by intercalated cells, secreted in variable amounts thru leak channels of principal cells

36. DCT & collecting duct

37. Tubular secretion • Secretion of H+ helps control ___________ • Secretion of others for ____________ from body • PCT • H+ and NH4+ ions, urea • DCT • H+ ions, (K+ by principal cells at end of DCT) • Collecting duct • K+/ H+ /NH4+ ions (depending on salt, pH balance)

38. Hormonal effects table 26.4 • Angiotensin II-(released when blood volume,  bp) •  GFR • Stim antiporter reabsorb Na+, Cl-, H2O in PCT • Stim release aldosterone • Aldosterone: ( plasma K+) • K+ secretion, Na+, Cl-, H20 reabsorbed • ADH- ( osm of ECF or  blood volume) • water reabsorption  in DCT • ANP- (stim by atria stretch,  blood volume) •  secretion of Na+ (natriuresis) • Suppress reabsorption at PCT •  urine output (diuresis) • ANP suppresses ADH & aldosterone secretion

39. Figure 26.17

40. Dilute & concentrated, fig 26.18 • Body __________ depends largely on kidney • Large volume, dilute urine when fluid intake  • Asc LOH & DCT rel impermeable to water • End of DCT & collecting duct impermeable to water when ADH ________ • Small volume, concentrated: fluid intake  • ADH enabled by osmotic gradient • Differences in solute & water permeability along LOH & collecting duct • Countercurrent flow in Des & Asc LOH

41. Dilute urineformation

42. Countercurrent mechanism • Hairpin shape of LOH- countercurrent flow • Descending limb: one direction • Very permeable to water • I.F. osmolarity > than inside tube  water→ out • As fluid moves down- gradient, osmolarity ↑ • Impermeable to solutes except urea • Ascending limb: opposite direction • Impermeable to water • Symporters reabsorb Na+, Cl- • Fluid osmolarity  as ascending

43. Countercurrent mechanism (2) • ____________: loops working similar to LOH • Descending- renal medulla I.F. more [ ] • More Na+, Cl-, urea diffuse into blood • Blood osmolarity  • Ascending- I.F. increasingly less [ ] • Ions diffuse out of Asc vasa recta • Reabsorbed water diffuses from I.F.  vasa recta • Osmolarity of blood leaving vasa recta only slightly higher than what entered • O2 & nutrients dropped off w/out  gradient

46. ORGANIC Urea Creatinine Uric acid INORGANIC Chloride Sodium Potassium Sulfates Phosphates Ammonia Calcium Magnesium Constituents of urine (lab, p60)

47. Diuretics • ______________ – elevated urine flow rate • Substances slow renal reabsorption of water • Often prescribed for _________________ • Lower blood volume  lower bp • Most interfere w/mechanism for Na+ reabsorption • Naturally occurring: • Caffeine- inhibits Na+ reabsorption • Alcohol- inhibits ADH secretion

48. Dialysis- “to separate” • _________ of large solutes from smaller ones by diffusion thru selectively permeable mem • Kidneys so impaired that unable to function • __________dialysis- filter patient’s blood by removing wastes, excess electrolytes & fluids and return blood to patient • Hemodialyzer, dialysis membrane • Dialysate- solution formed to maintain diffusion gradients & add needed substances • Peritoneal dialysis- catheter & dialysate

49. Flow from nephron to urethra • (Nephron: Bowman’s capsulePCTLOHDCT) • Collecting duct  • Papillary duct  • Minor calyx  • Major calyx  • Renal pelvis  • Ureter  • Urinary bladder  • Urethra

50. Micturition • Urination or voiding • Discharge of urine from urinary bladder • Voluntary (SNS) & involuntary (ANS) muscle contractions • When 200-400mL  stretch receptors trigger ________________- S2-S3  spinal reflex • Contraction of detrusor • Relaxation- internal urethral sphincter muscle • Filling causes sensation before reflex occurs • _______________- lack of voluntary control