Urinary System. Crash Course

• The lungs exhale carbon dioxide and the colon will eventually poop out unusable stuff and old cell-parts
• Urinary system


  The system that sorts and disposes of chemical waste
• Kidneys


  • Regulate water volume, ion salt concentrations, and pH levels
  • Influence red blood cell production and blood pressure
  • Filter toxic leftovers from the blood
• How the kidneys filter blood

  1. Blood enters kidneys

  2. Filtered in glomerulus

  3. Filtrate goes to renal tubule

  4. Reabsorption of useful substances

  5. Remaining filtrate becomes urine
• Filtrate

  The stuff that gets squeezed out of the blood into the glomerulus
• Parts of the renal tubule

  1. Proximal convoluted tubule

  2. Loop of Henle

  3. Distal convoluted tubule

  4. Collecting duct
• Proximal convoluted tubule


  Reabsorbs useful substances like ions, glucose, and water back into the blood
• Loop of Henle


  Creates a salt concentration gradient in the medulla to drive water reabsorption
• Distal convoluted tubule and collecting duct


  Where the remaining filtrate becomes urine
• Urea


  A less toxic compound produced from ammonia, which is filtered out into urine
• Urea can degrade back into ammonia
• The kidneys filter about 120 to 140 liters of blood every day
• Nephrons


  The microscopic filtering units in the kidneys, where filtration, reabsorption, and secretion occur
• Steps in nephrons


  1. Filtration in glomerulus

  2. Reabsorption in renal tubule

  3. Secretion of waste products
• The kidneys use urea to help create the salt concentration gradient in the medulla
• Urea recycling

  Urea escapes the urine, finds its way back into the loop of Henle, and runs the course again
• Tubular secretion transports select waste products that have already made their way into the blood back into the urine
• Micturition


  The scientific term for urination
• All mammals and most animals urinate to remove toxins and maintain water-volume homeostasis or blood pressure
• Freshly peed urine


  95% water, slightly acidic
• Urine composition can indicate

  • Urinary tract infection (cloudy with white blood cells)
  • Diabetes (sweet smell and high glucose)
  • Internal bleeding (pink color)
  • Pregnancy, overexertion, high blood pressure, or heart failure (high protein)
• Regulation of urine production


  1. Glomerular filtration

  2. Autoregulation of glomerular filtration rate

  3. Hormonal regulation by antidiuretic hormone (ADH)
• Glomerular filtration rate


  The constant rate of blood flow through the glomeruli in the kidneys
• Autoregulation


  The kidneys' intrinsic ability to maintain a constant glomerular filtration rate despite changes in blood pressure
• Antidiuretic hormone (ADH)


  A hormone secreted by the posterior pituitary gland that helps the body retain water
• Caffeine and alcohol inhibit ADH release


  Leads to increased urine production and dehydration
• Movement of urine from kidneys to bladder

  1. Ureters use peristalsis to move urine

  2. Bladder stores urine temporarily
• Bladder


  • Hollow, collapsible sac that temporarily stores urine
  • Consists of an inner mucosa, a thick muscular layer (detrusor), and a fibrous outer membrane
• Micturition


  The act of urinating, or the excretion of urine
• Regulation of urination


  1. Stretch receptors in bladder wall send impulses to spinal cord and brain

  2. Parasympathetic neurons are excited, sympathetic neurons inhibited

  3. Detrusor muscle contracts, internal urethral sphincter opens, external urethral sphincter relaxes
• Pontine storage area


  Brain region that inhibits urination
• Pontine micturition center


  Brain region that triggers urination