Urinary

• Urinary system


  Consists of the paired kidneys and ureters, the bladder, and the urethra
• Role of the urinary system

  • Ensure optimal properties of the blood, which the kidneys continuously monitor
  • Regulation of the balance between water and electrolytes and the acid-base balance
  • Excretion of metabolic wastes along with excess water and electrolytes in urine
  • Excretion of many bioactive substances, including many drugs
  • Secretion of renin, a protease important for regulation of blood pressure
  • Secretion of erythropoietin, a glycoprotein growth factor that stimulates erythrocyte production
  • Conversion of the steroid prohormone vitamin D to the active form
• Gluconeogenesis


  Making glucose from amino acids to supplement this process in the liver during starvation or prolonged fasting
• Kidneys


  • Approximately 12-cm long, 6-cm wide, and 2.5-cm thick in adults
  • Concave medial border (hilum) where nerves enter, ureter exits, and blood and lymph vessels enter and exit
  • Convex lateral surface covered by a thin fibrous capsule

  
• Renal pelvis


  Upper end of the ureter that divides into major and minor calyces
• Renal parenchyma


  Outer renal cortex and inner renal medulla

  
• Renal cortex


  Darker stained region with many round corpuscles and tubule cross sections
• Renal medulla


  Consists mostly of aligned linear tubules and ducts

  
• Renal pyramids


  Conical structures in the medulla with bases meeting the cortex
• Renal lobe


  A pyramid plus the cortical tissue at its base and extending along its sides

  
• Medullary rays


  Parallel ducts and tubules extending from the medulla into the cortex
• Renal lobule


  Medullary rays and their associated cortical tissue

  
• Renal papilla


  Tip of each pyramid that projects into a minor calyx
• Nephron


  Functional unit of the kidney, consisting of a corpuscle and a long, simple epithelial renal tubule

  
• Parts of a nephron

  • Renal corpuscle
  • Proximal tubule
  • Loop of Henle
  • Distal tubule
  • Connecting tubule
• Renal corpuscle


  Initial dilated part enclosing a tuft of capillary loops and the site of blood filtration, always located in the cortex

  
• Proximal tubule


  Long convoluted part located entirely in the cortex, with a shorter straight part that enters the medulla
• Loop of Henle


  In the medulla, with a thin descending and a thin ascending limb
• Distal tubule


  Consisting of a thick straight part ascending from the loop of Henle back into the cortex and a convoluted part completely in the cortex
• Connecting tubule


  Short minor part linking the nephron to collecting ducts
• Cortical nephrons


  Located almost completely in the cortex
• Juxtamedullary nephrons


  Lie close to the medulla and have longer loops of Henle extending deeper into the medulla
• Polycystic kidney disease is an inherited disorder in which normal cortical organization of both kidneys is lost due to the formation of multiple, large, fluid-filled cysts
• Renal artery


  Divides into segmental arteries at the hilum

  
• Interlobar arteries


  Branch from the segmental arteries and extend between the renal pyramids toward the corticomedullary junction
• Arcuate arteries


  Divide from the interlobar arteries and run in an arc along the corticomedullary junction at the base of each renal pyramid
• Interlobular arteries


  Radiate from the arcuate arteries, extending deeply into the cortex
• Afferent arterioles


  Arise from the interlobular arteries and divide to form the glomerular capillary loops
• Efferent arterioles


  Blood leaves the glomerular capillaries and forms another capillary network, usually the peritubular capillaries in the cortex
• Vasa recta


  Efferent arterioles from the juxtaglomerular corpuscles branch repeatedly to form parallel tassel-like bundles of capillary loops that penetrate deep into the medulla
• The cortex receives over 10 times more blood than the medulla
• There are many different glomerular diseases involving the renal corpuscles, with different causes calling for different treatments
• Urine formation


  • Filtration
  • Tubular secretion
  • Tubular reabsorption
• The number of nephrons decreases substantially in older adults, a process accelerated by high blood pressure
• If a kidney is donated for transplant, the remaining kidney undergoes compensatory growth with cellular hypertrophy in the proximal parts of the nephron tubules and an increased rate of filtration, which allow normal renal function to continue

  
• Inflammation within the glomeruli, or glomerulonephritis, usually stems from humoral immune reactions
• Renal corpuscle


  Contains a tuft of glomerular capillaries, surrounded by a double-walled epithelial capsule called the glomerular (Bowman) capsule

  
• Capsular (urinary) space


  Between the two capsular layers, receives the fluid filtered through the capillary wall and the visceral layer
• Vascular pole


  Where the afferent arteriole enters and the efferent arteriole leaves the renal corpuscle
• Tubular pole


  Where the proximal convoluted tubule begins