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Chapter 26

Chapter 26. The Urinary System. Learning Objectives. Identify the components and functions of the urinary system Describe the location and structural features of the kidneys Describe the structure of a nephron, and outline the processes involved in the formation of urine

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Chapter 26

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  1. Chapter 26 The Urinary System

  2. Learning Objectives • Identify the components and functions of the urinary system • Describe the location and structural features of the kidneys • Describe the structure of a nephron, and outline the processes involved in the formation of urine • List and describe the factors that influence filtration pressure and the rate of filtrate formation

  3. SECTION 26-1An Overview of the Urinary System

  4. Functions of the urinary system • Excretion • The removal of organic waste products from body fluids • Elimination • The discharge of waste products into the environment • Homeostatic regulation of blood plasma • Regulating blood volume and pressure • Regulating plasma ion concentrations • Stabilizing blood pH • Conserving nutrients

  5. Urinary system includes: • The kidneys • Produce urine • The ureters • The urinary bladder • Stores urine • The urethra

  6. Figure 26.1 An introduction to the Urinary System Figure 26.1

  7. SECTION 26-2The Kidneys

  8. The kidneys • Left kidney extends slightly more superiorly than right • Both kidneys and adrenal glands are retroperitoneal • Hilus • Entry for renal artery and renal nerves • Exit for renal veins and ureter

  9. Figure 26.2 The Position of the Kidneys Figure 26.2a, b

  10. Figure 26.3 The Urinary System in Gross Dissection Figure 26.3

  11. Sectional anatomy of the kidneys • Superficial outer cortex and inner medulla • The medulla consists of 6-18 renal pyramids • The cortex is composed of roughly 1.25 million nephrons • Major and minor calyces along with the pelvis drain urine to the ureters

  12. Figure 26.4 The Structure of the Kidney Figure 26.4a, b

  13. Blood supply and innervation of the kidneys • Renal arteries branch repeated • Renal artery • Segmental artery • Interlobar artery • Arcuate artery • Interlobular artery • Afferent arterioles • Renal venules follow similar opposing pattern ending with renal veins

  14. Figure 26.5 The Blood Supply to the Kidneys Figure 26.5a, b

  15. Figure 26.5 The Blood Supply to the Kidneys Figure 26.5c, d

  16. The nephron consists of a renal corpuscle and renal tubule • The renal corpuscle is composed of • Bowman’s capsule and the glomerulus • The renal tubule consists of • Proximal convoluted tubule (PCT) • Loop of Henle • Distal convoluted tubule (DCT)

  17. Filtrate is produced at the renal corpuscle • Nephron empties tubular fluid into collecting system • Collecting ducts and papillary ducts form the collecting system

  18. Figure 26.6 A Representative Nephron Figure 26.6

  19. Nephron functions include: • Production of filtrate • Reabsorption of organic nutrients • Reabsorption of water and ions • Secretion of waste products into tubular fluid

  20. Two types of nephron • Cortical nephrons • ~85% of all nephrons • Located in the cortex • Juxtamedullary nephrons • Closer to renal medulla • Loops of Henle extend deep into renal pyramids • Responsible for greatest amount of water reabsorbed

  21. Figure 26.7 Cortical and Juxtamedullary Nephrons Figure 26.7a

  22. Figure 26.7 Cortical and Juxtamedullary Nephrons Figure 26.7b, c

  23. Renal tubule and blood flow • Blood travels from efferent arteriole to peritubular capillaries • Vasa recta • Renal tubule begins at renal corpuscle • Includes glomerulus and Bowman’s capsule • Blood leaves the nephron via the efferent arteriole

  24. Glomerulus anatomy • Podocytes cover lamina densa of capillaries • Project into the capsular space • Pedicels of podocytes separated by filtration slits

  25. Figure 26.8 The Renal Corpuscle Figure 26.8a, b

  26. Figure 26.8 The Renal Corpuscle Figure 26.8c, d

  27. Functional anatomy of the nephron • Proximal convoluted tubule (PCT) • Actively reabsorbs nutrients, plasma proteins and ions from filtrate • Released into peritubular fluid • Loop of Henle • Descending limb • Ascending limb • Each limb has a thick and thin section PLAY Animation: Urinary System Anatomy

  28. Functional anatomy of the nephron • Distal convoluted tubule (DCT) • Actively secretes ions, toxins, drugs • Reabsorbs sodium ions from tubular fluid PLAY Animation: Urinary System Dissection and Flythrough

  29. SECTION 26-3Principles of Renal Physiology

  30. Urine production maintains homeostasis • Regulating blood volume and composition • Excreting waste products • Urea • Creatinine • Uric acid

  31. Basic processes of urine formation • Filtration • Blood pressure • Water and solutes across glomerular capillaries • Reabsorption • The removal of water and solutes from the filtrate • Secretion • Transport of solutes from the peritubular fluid into the tubular fluid

  32. Carrier Mediated Transport • Filtration in the kidneys modified by carrier mediated transport • Facilitated diffusion • Active transport • Cotransport • Countertransport • Carrier proteins have a transport maximum (Tm) • Determines renal threshold

  33. Reabsorption and secretion • Accomplished via diffusion, osmosis, and carrier-mediated transport • Tm determines renal threshold for reabsorption of substances in tubular fluid

  34. Renal function • Most regions of the nephron perform a combination of functions • General functions can be identified • Filtration in the renal corpuscle • Nutrient reabsorption along the PCT • Active secretion at PCT and DCT • Loops of Henle regulate final volume and solute concentration

  35. Figure 26.9 An Overview of Urine Formation Figure 26.9

  36. SECTION 26-4Renal Physiology: Filtration and the Glomerulus

  37. Filtration pressures - Glomerular filtration • Occurs as fluids move across the glomerulus • In response to glomerular hydrostatic pressure (GHP) and blood pressure in the glomerular capillaries • Capsular hydrostatic pressure (CsHP) opposes GHP • Blood colloid osmotic pressure (BCOP) opposes GHP • Net hydrostatic pressure (NHP) = GHP – CsHP • Filtration (FP) = NHP – BCOP

  38. Figure 26.10 Glomerular Filtration Figure 26.10

  39. Figure 26.10 Glomerular Filtration Figure 26.10a, b

  40. Glomerular filtration rate (GFR) • Amount of filtrate produced in the kidneys each minute • Factors that alter filtration pressure change GFR

  41. SECTION 26-5Renal Physiology: Reabsorption and Secretion

  42. Reabsorption and secretion at the PCT • Glomerular filtration produces fluid similar to plasma without proteins • The PCT reabsorbs 60-70% of the filtrate produced • Reabsorption of most organic nutrients • Active and passive reabsorption of sodium and other ions • Reabsorption of water • Secretion also occurs in the PCT PLAY Animation: Early Filtrate Processing PLAY Animation: Glomerular filtration

  43. Figure 26.12 Transport Activities at the PCT PLAY Animation: Proximal Convoluted Tubule Figure 26.12

  44. The loop of Henle and countercurrent multiplication • Countercurrent multiplication • Between ascending and descending limbs of loop • Creates osmotic gradient in medulla • Facilitates reabsorption of water and solutes before the DCT • Permits passive reabsorption of water from tubular fluid

  45. Figure 26.13 Countercurrent Multiplication and Concentration of Urine Figure 26.13a

  46. Figure 26.13 Countercurrent Multiplication and Concentration of Urine Figure 26.13b

  47. Figure 26.13 Countercurrent Multiplication and Concentration of Urine Figure 26.13c

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