urinary system

• Formation of urine


  1. Filtration

  2. Reabsorption

  3. Secretion
• Kidneys


  • Act as vital organs in maintaining homeostasis
• Filtration


  Process of forming urine by filtering blood in the glomerulus
• Reabsorption


  Process of returning filtered molecules back to the blood
• Secretion


  Process of transferring materials from peritubular capillaries to the renal tubular lumen
• Urine volume


  Mechanisms that control it, including normal amount and composition
• Urine elimination


  Process of urine passing from the bladder through the urethra to exit the body
• Kidneys


  Location under back muscles, behind parietal peritoneum, just above waistline
• Kidney structure


  • Renal cortex
  • Renal medulla made up of renal pyramids and columns
• Nephron


  Microscopic unit of the kidney consisting of renal corpuscle and renal tubules
• Renal corpuscle


  Bowman capsule and glomerulus
• Kidney function


  • Excrete toxins and nitrogenous wastes
  • Regulate levels of many chemicals in blood
  • Maintain water balance
  • Help regulate blood pressure via secretion of renin
  • Secrete erythropoietin (EPO)
• Urine


  Made in the kidney, drains into the renal pelvis, then down the ureter to the urinary bladder, and passes from the bladder through the urethra to exit the body
• Renal blood vessels


  Renal artery, interlobar arteries, arcuate arteries, interlobular arteries, afferent arterioles, glomerulus, efferent arterioles, peritubular capillaries, interlobular veins, arcuate veins, interlobar veins, renal vein
• Nephron tubules


  1. Glomerular (Bowman's) capsule

  2. Proximal convoluted tubule

  3. Descending and ascending limbs of the loop of Henle

  4. Distal convoluted tubule

  5. Collecting duct
• Juxtamedullary nephrons


  Better at making concentrated urine
• Cortical nephrons


  Less efficient at concentrating urine
• Glomerular filtration


  Process of fluid entering the glomerular capsule
• Glomerular filtration rate (GFR)


  Volume of filtrate produced by both kidneys each minute, normally 115-125 ml
• Renal autoregulation


  • GFR is maintained at a constant level even when blood pressure fluctuates greatly
• Reabsorption


  Return of filtered molecules to the blood
• Proximal tubule reabsorption


  • 65% of salt and water is reabsorbed, but still too much filtrate
  • An additional 20% of water is reabsorbed through the descending limb of the Loop of Henle
  • Final 15% of water (~27 L) is absorbed later in the nephron under hormonal control
• Countercurrent multiplier system


  Mechanism that helps set up solute concentration gradients
• Vasa recta


  Specialized blood vessels around the loop of Henle
• Urea


  Waste product of protein metabolism that contributes to the countercurrent system
• Collecting duct


  Last stop in urine formation, permeability to water depends on availability of aquaporin channels
• ADH (antidiuretic hormone)


  Secreted from the posterior pituitary gland, decreases the amount of urine by making collecting ducts permeable to water
• Aldosterone


  Secreted by the adrenal cortex, stimulates the tubules to reabsorb sodium at a faster rate
• Atrial natriuretic hormone (ANH)

  Secreted from the heart's atrial wall, stimulates kidney tubules to secrete more sodium and thus lose more water
• Anuria


  Absence of urine
• Oliguria


  Scanty amount of urine
• Polyuria


  Unusually large amount of urine
• Tubular secretion


  Transfer of materials from peritubular capillaries to the renal tubular lumen
• Inulin clearance


  Considered the gold standard for measuring GFR because inulin has all the properties of an ideal marker
• Juxtaglomerular apparatus


  Specialized structure that regulates blood pressure and the filtration rate of the glomerulus
• Regulation of plasma Na+

  Decrease in plasma Na+ results in fall in blood volume, sensed by juxtaglomerular apparatus which secretes renin
• Acid-base regulation


  Kidneys maintain blood pH by reabsorbing bicarbonate and secreting H+
• Urinalysis


  Physical, chemical, and microscopic examination of urine to detect signs of disease
• Ureter


  Narrow, long tubes that drain urine from the renal pelvis to the urinary bladder
• Urinary bladder


  Elastic muscular organ that stores urine before voiding