Chapter 26: The Urinary System

1. Chapter 26:The Urinary System Primary sources for figures and content: Marieb, E. N. Human Anatomy & Physiology. 6th ed. San Francisco: Pearson Benjamin Cummings, 2004. Martini, F. H. Fundamentals of Anatomy & Physiology. 6th ed. San Francisco: Pearson Benjamin Cummings, 2004.

2. Urinary System • Components • Kidneys • Urinary Tract • Ureters • Urinary Bladder • Urethra Figure 26–1

3. Functions of the Urinary System • Excretion by the Kidneys: • removal of organic wastes from body fluids • Elimination by the Urinary Tract: • discharge of waste products • Homeostatic regulation of plasma volume and solute concentrations by the kidneys: • Blood volume, BP • Concentration of ions • Stabilize blood pH • Conserve nutrients • Assist liver: deamination, detoxification

4. Functions of the Urinary System 4. Other kidney functions: • Gluconeogenesis during starvation • Produce renin to regulate BP • Produce erythropoietin for RBC production • Convert Vitamin D to calcitriol for calcium absorption in the GI tract

5. The location and structures of the kidneys.

6. Gross Anatomy of the Urinary System Figure 26–3

7. Kidneys • 1% body weight • Retroperitoneal, posterior abdominal wall • Adrenal gland anchored superior • 3 layers CT anchor kidneys • Renal capsule: - collagen fibers covering organ • Adipose capsule: - adipose cushion around the renal capsule • Renal fascia: - collagen fibers fused to renal capsule and deep fascia of body wall and peritoneum

8. Kidneys • Renal ptosis = floating kidney • Cause  Starvation or injury • Result  Kidney becomes loose from body wall • Kidney could twist blood vessels or ureters

9. The Structure of the Kidney Figure 26–4

10. Kidney • Hilum (Hilus): • Point of entry for renal artery and renal nerves • Ureters enter and exit • Hilus opens to renal sinus • Renal sinus lined with renal capsule that is contiguous with outside

11. Kidney • Kidney has two layers 1. Cortex = superficial • Contact renal capsule • Houses filtration structures = nephrons 2. Medulla = 6-18 renal pyramids • Parallel bundles of collection tubules • Apex = papilla, points toward renal sinus • Kidney divided into sections: renal lobes • Renal lobe = • renal pyramid + surrounding cortex called renal columns • Lobe is site for urine production

12. Urine Production • Nephron (cortex)  collecting ducts (medulla)  papilla  minor calyx major calyx  renal pelvis • Renal pelvis • Fills majority of real sinus • Funnels urine into ureters • Pyelonephritis • Inflammation of kidney • Infection usually enters from ureter and spreads up through ducts to nephron

13. Blood Supply to the Kidneys Figure 26–5

14. Blood Supply and Innervation to Kidney • Receives 20-25% cardiac output • Highly vascularized, many capillaries involved in filtration (nephrons) • Innervation from Renal Plexus controlled by ANS • Most is sympathetic to • Adjust rate of urine formation - Change BP and flow at nephron • Stimulate release of renin - Restricts water and sodium loss at nephron

15. Blood Supply and Innervation to Kidney • Two important capillary beds associated with each nephron 1. Glomerulus = filtration 2. Peritubular capillaries: - reclaim filtrate, concentrate urine • Both connected to arterioles only (not for oxygen exchange) • Afferent arteriole  capillary  efferent arteriole

16. Glomerulus • Consists of 50 intertwining capillaries • Blood delivered via afferent arteriole • Blood leaves in efferent arteriole: • flows into peritubular capillaries • which drain into small venules • and return blood to venous system

17. The Nephron and Collecting System Figure 26–6

18. Nephron • Two types of nephrons • Cortical nephron = Majority • In cortex, short loop of Henle • Juxtamedullary nephrons = 15% • At cortex/medulla interface • Long loops of Henle • Important for water conservation and concentrated urine

19. Cortical and Juxtamedullary Nephrons Figure 26–7

20. Renal Corpuscle • Site of filtration • 2 parts 1. Glomerular capsule • Thin parietal epithelium, forms capsule around glomerulus 2. Glomerulus • Fenestrated capillaries covered by podocytes • Podocytes are on the visceral epithelium • Wrapped around the capillaries, to create filtration slits on surface of capillaries • Slits smaller than fenestrations in glomerular capillaries to restrict filtration of large molecules

21. The Renal Corpuscle Figure 26–8

22. Renal Corpuscle • Golmerulonephritis • Inflammation of glomeruli • Prevents filtration • Can be result of antigen/Ab complexes trapped in filtration slits following allergy or blood infection

23. The Nephron and Collecting System Figure 26–6

24. Renal Tubule • Reabsorption to process raw filtrate into urine • 3 parts 1. PCT (proximal convoluted tubules) • Simple cuboidal epithelium with microvilli • Reabsorbs organic nutrients, ions, water, small plasma proteins from filtrate exiting glomerular capsule 2. Loop of Henle • Simple squamous epithelium • Reabsorbs Na+, Cl-, H2O form filtrate • Important to regulate volume and solute concentration of urine • Descending and ascending limbs

25. Renal Tubule 3. DCT (distal convoluted tubules) • Simple cuboidal epithelium • Flat surface • Four important functions • Secretion • Reabsorb Na+ and Ca++ from filtrate • Optional H2O reabsorption from filtrate under hormonal control • Contribute to formation of Juxtaglomerular Apparatus

27. Table 26–1

28. Juxtaglomerular Apparatus (JGA) • Consists of two cell types • Endocrine cells of DCT = macula densa • Granular cells of apparent arteriole = Juxtaglomerular cells • Together cells monitor blood and produce • Renin: Enzyme, restricts Na+ and H2O at nephron • Erythropoietin: hormone, stimulates RBC production

30. Collecting System • Collecting ducts + papillary ducts = nephrons  1 collecting duct (renal pyramid)  Many collecting ducts  1 papillary duct • Final osmotic concentration of filtrate adjusted by collecting duct, after this urine is complete and exits kidney: • Papillary ducts (renal papilla)  minor calyx  major calyx  renal pelvis  ureter • Polycystic Kidney Disease • Genetic, cysts form that cause swelling of kidney tubules, compression reduces function

31. KEY CONCEPT • Kidneys remove waste products from blood • Nephrons are primary functional units of kidneys • Kidneys help regulate: • blood volume and pressure • ion levels • blood pH

32. Which portion of the nephron is NOT in the renal cortex? proximal convoluted tubule distal convoluted tubule collecting duct loop of Henle

33. Why don’t plasma proteins pass into the capsular space under normal circumstances? glomerular capillary pores are too small glomerular blood pressure is too low glomerular filtration rate is too low glomerular blood flow is too slow

34. Damage to which part of the nephron would interfere with the control of blood pressure? juxtaglomerular apparatus Bowman’s capsule PCT loop of Henle

35. Renal Physiology

36. Renal Physiology • Urinary system functions to regulate blood volume and concentration • Removes wastes and produce urine • Filtrate = • Everything in blood plasma except large proteins and cells • Urine = metabolic waste, 1% filtrate

37. Common Wastes 1. Urea: from catabolism of amino acids 2. Creatinine: from catabolism or damage of skeletal muscle tissue • Creatine phosphate is energy storage of muscle 3. Uric acid: from recycling of RNA 4. Urobilin: from breakdown of hemoglobin (yellow color) • All wastes excreted as solution in water • Loss of filtering  toxic waste buildup • death in a few days • Dialysis  blood filtering machine used for patients with kidney failure

38. Urine Formation 1. Glomerular Filtrations • Blood hydrostatic pressure forces water and solutes through glomerular wall 2. Tubular Reabsorption • Selective uptake of water and solutes from filtrate 3. Tubular Secretion • Transport of wastes from capillaries to tubules

39. An Overview of Urine Formation Figure 26–9 (Navigator)

40. 1. Glomerular Filtration • Occurs through filtration membrane • Fenestrated endothelium of glomerular capillaries - Restricts cells • Podocytes (visceral epithelium of capsule) - Filtration slits restrict solutes protein sized and larger • Fused basal lamina for both

41. 1. Glomerular Filtration • Filtrations depends on • Large surface area • High glomerular blood pressure • Good permeability • Glomerular Filtration Rate (GFR) • Amount of filtrate kidneys produce/minute • ~125 ml/min  180L/day • 99% reabsorbed, 1% lost as urine • Drop in blood pressure = decrease GFR • Decrease 15% BP = 0 GFR

42. Glomerular Filtration Filtration is passive but all small solutes escape e.g. glucose, amino acids, etc. Figure 26–10

43. Regulation of Filtrations3 Levels of GFR Control • Autoregulation (local level) • Hormonal regulation (initiated by kidneys) • Autonomic regulation (by sympathetic division of ANS)

44. 1. Autoregulation of GFR • Functions to maintain constant GFR with normal blood pressure fluctuations in systemic arteriole pressure A. Reduced blood flow/BP triggers • Dilation of afferent arteriole and glomerular capillaries • Constriction of efferent arteriole • All functions to INCREASE PRESSURE at the glomerulus to INCREASE GFR B. High blood flow/BP triggers • Constriction of afferent arteriole and glomerular capillaries • Dilation of efferent arteriole • All functions to DECREASE PRESSURE at the glomerulus to DECREASE GFR

45. 2. Hormonal Regulation • Extrinsic regulation aimed at maintaining systemic blood pressure A. Renin = Enzyme released by juxtaglomerular apparatus in response to: 1. Decline in BP in kidney 2. Decline in osmotic concentration of filtrate 3. Direct sympathetic stimulation

46. 2. Hormonal Regulation A. Renin = • Renin activates angiotensin in blood to form Angiotensin II which triggers 1. Arteriole constriction to elevate BP 2. Secretion of aldosterone from adrenal glands • Aldosterone promotes sodium reabsorption in kidney tubules 3. Thirst 4. Release of ADH from pituitary (ADH promotes water uptake in tubules) • Effect = • Increase blood volume • Decrease urine production

47. 2. Hormonal Regulation B. Natriuretic Peptide = • Hormone released in response to stretching in heart or aorta (increase blood volume) • Triggers 1. Dilation of afferent arteriole 2. Constriction of efferent arteriole • Effect = • Increase GFR • Increase Urine Production • Decrease blood volume

48. 3. Autonomic Nervous System Regulation • Sympathetic causes vasoconstriction • Decrease GFR • Decrease Urine Production • Prolonged sympathetic stimulation can cause hypoxia of kidneys and waste accumulation in blood

49. Response to Reduction in GFR Figure 26–11

50. KEY CONCEPT • Glomeruli produce about 180 L of filtrate per day (70 times plasma volume) • Almost all fluid volume must be reabsorbed to avoid fatal dehydration