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The Urinary System: Organs, Functions, and Structure

Explore the organs of the urinary system, their functions, and the structure of the kidneys. Learn about the blood supply to the kidneys, the nephron, and the filtration process. Discover the different segments of a nephron and the two types of nephrons. Understand the concept of glomerular filtration rate (GFR) and the regulation of urine production.

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The Urinary System: Organs, Functions, and Structure

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  1. Chapter 23-1 The Urinary System

  2. Organs of the Urinary System • The kidneys - produce urine • The ureters • The urinary bladder - stores urine • The urethra

  3. Functions of the Urinary System • Excretion(kidney) • The removal of organic wastes, water, and ions from body fluids • Elimination (ureters, bladder and urethra) • The discharge of waste products into the environment • Homeostatic regulation (kidney) • Regulating blood volume and pressure • Regulating plasma ion concentrations • Stabilizing blood pH • Conserving nutrients • Synthesizing vitamin D and regulating hormones

  4. The kidneys • Left kidney is 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 • Renal capsule- collagen fibers, prevent distension • Adipose layer and renal fascia

  5. Position of the kidneys

  6. Sectional anatomy of the kidneys • Superficial outer cortex and inner medulla • The medulla consists of 6-18 renal pyramids • Minor and major calyces connect to form therenal pelvis which drains urine to the ureters • Functional unit of the kidney is the nephron • roughly 1.25 million nephrons per kidney • Connect together to form collecting ducts • Two capillary beds intimately work with the nephron and collecting ducts

  7. Structure of the Kidney Marieb Figure 25.3a

  8. Blood supply of the kidneys • Renal artery • Segmental artery • Interlobar artery - run between the pyramids • Arcuate artery - seperates the cortex from medulla • Interlobular artery (cortical radiate artery) • Afferent arterioles • Efferent arterioles • Renal venous system follows similar opposing pattern ending with renal veins

  9. The Blood Supply to the Kidneys

  10. The Blood Supply to the Kidneys #2 From Martini Figure 26.5a, b

  11. Afferent and Efferent arterioles Efferent arteriole Afferent arteriole Glomerulus

  12. Capillary beds • Glomerulus • Vasa recta

  13. Nephron • Three functions • Filtration • Reabsorption(back into the blood) • organic nutrients • water • ions • Secretion(from the blood into tubular fluid) • drugs and toxins • ions • acids • nitrogenous wastes

  14. Nephron • Functional unit of the kidney is the nephron • 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) • Nephrons connect to form collecting ducts

  15. A Representative Nephron

  16. Functional anatomy of the nephron Proximal convoluted tubule (PCT) Reabsorbs nutrients, plasma proteins and ions from filtrate Secretion of drugs and toxins Loop of Henle Descending limb Ascending limb Each limb has a thick and thin section Involved in concentration and dilution of urine

  17. Distal convoluted tubule (DCT) Secretes ions, acid, drugs Reabsorbs sodium ions and water from tubular fluid Macula densa - specialized cells that regulate glomerular filtration Juxtaglomerular cells (JG cells)- specialized smooth muscle cells in the afferent arteriole that release renin Functional anatomy of the nephron

  18. Overview of Nephron Segments Functions Figure 26.6

  19. Two types of nephron • Cortical nephrons • ~85% of all nephrons • Located high in the cortex • Juxtamedullary nephrons • Closer to renal medulla • Loops of Henle extend deep into renal pyramids

  20. Cortical and Juxtamedullary Nephrons Also see Saladin figs 23.6 & 23.8c

  21. Renal corpuscle • Bowman’s capsule • 2 layers of simple squamous epithelium • Glomerulus • Podocytes- (specialized epithelial cells) cover lamina densa of capillaries • Project into the capsular space • Pedicels (foot processes) of podocytes separated by filtration slits • Mesangeal cells- similar to vascular smooth muscle cells

  22. Renal corpuscle (Saladin fig 23.7)

  23. Filtration membrane Figure 25.7a

  24. Filtration slits (Also see Saladin fig 23.10 for excellent SEM and TEM photos) RBC Marieb Figure 25.7b, c

  25. 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

  26. Glomerular capillary perfusion hydrostatic pressure x oncotic pressure

  27. Filtration pressures Afferent arteriole Efferent arteriole

  28. Glomerular filtration rate (GFR) • Amount of filtrate produced in the kidneys each minute (~125 ml/min) • creatinine clearance • inulin clearance • Autoregulation - GFR remains relatively constant despite changes in blood pressure • Renal blood flow (21% C.O. - 1176 ml/min) • Renal plasma flow (650 ml/min) • Filtration fraction (~19%) 125 x 60 x 24 =180,000 ml /day Average blood vol 5-6 L

  29. Calculation of GFR GFR = Uinulin xV _________________________________ Pinulin

  30. Autoregulation of RBF and of GFR Renal blood flow GFR 0 25 50 75 100 125 150 200 Blood pressure

  31. Autoregulation (for decreased blood pressure) • Changes in blood pressure are sensed and result in • afferent arteriole relaxation • efferent arteriole constriction • change in podocyte and capillary surface area by relaxation of mesangeal cells • altered oncoctic and osmotic pressure Glomerulus Afferent arteriole Efferent arteriole PCT Note when BP increases the opposite affects occur

  32. Several levels of control of GFR • Myogenic control • Paracrine factors • Neural reflexes (sympathetic nerves) • Hormonal

  33. Macula Densa and JG Apparatus Tubulogolmerular feedback (See Saladin fig 23.14 for feedback loop)

  34. Hormonal control of GFR • A drop in filtration pressure stimulates Juxtaglomerular apparatus (macula densa & JG cells) • Releases renin and erythropoietin • Renin coverts angiotensinogen to angiotensin I which is converted to angiotensin II via ACE (see fig 23.15) • Ang II causes • constriction of systemic arterioles • constricts efferent arteriole more than the afferent arteriole • causes aldosterone and ADH release

  35. Hormonal control of GFR • Aldosterone stimulates the reabsorption of sodium • ADH increases the reabsorption of water and activates thirst • ANPandBNP cause afferent arteriole dilation and efferent arteriole constriction

  36. Response to a change in the GFR Excess Cl

  37. Response to a Reduction in the GFR Figure 26.11b

  38. Sympathetic activation • Produces powerful vasoconstriction of afferent arterioles • Decreases GFR and slows production of filtrate • Changes the regional pattern of blood flow • Alters GFR • Stimulates release of renin by JG apparatus

  39. Summary of GFR regulation Figure 25.10

  40. Summary table of GFR, RPF, FF

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