URINARY SYSTEM

• Excretory system


  Removes nitrogenous wastes from the blood
• Urinary system


  3 functions: excretion, elimination, maintains homeostasis
• Micturition

  1. Stretch receptors activated

  2. Detrusor muscle contracts

  3. Forces urine past internal urethral sphincter

  4. External urethral sphincter under voluntary control
• Micturition reflex center


  Triggered by distension of the bladder, located in the spinal cord
• Neural and emotional factors may lead to incontinence
• Automatic bladder


  Complete loss of voluntary control over urination, requires catheritization
• Urinary system components

  • Pair of kidneys
  • Pair of ureters
  • Urinary bladder
  • Urethra
• Kidneys


  • Reddish brown, bean shaped, smooth surface
  • Located retroperitoneally in the posterior wall of the abdominal cavity
• Renal medulla


  Inner region of the kidney, contains renal columns, pyramids, loop of Henle, collecting ducts
• Renal cortex


  Outer region of the kidney, contains glomeruli, proximal convoluted tubules, distal convoluted tubules
• Renal pelvis


  Basin-like area of the kidney that joins the ureter
• Renal calyx


  Extensions of the renal pelvis that drain the apex of the renal pyramids
• Renal columns


  Cortex-like tissue that runs through the medulla
• Kidneys


  • Remove nitrogenous wastes, regulate metabolic processes, maintain electrolyte/water/acid-base balance, secrete erythropoietin, use renin to regulate blood pressure
• Renal disease


  Kidney transplant, hemodialysis, peritoneal dialysis
• Renal arteries


  Supply kidneys with blood, enter at the hilum
• Renal veins


  Carry blood from the kidneys back to the heart, exit at the hilum
• Nephron


  Functional unit of the kidney, contains renal corpuscle and renal tubule
• Urine formation

  1. Glomerular filtration

  2. Tubular reabsorption

  3. Tubular secretion
• Glomerular filtration


  Water and dissolved substances filtered out of the glomerulus into Bowman's capsule
• Glomerular filtrate


  Similar to plasma, mostly water, salt, glucose, amino acids, urea
• Glomerular filtration rate


  125 mL/minute, 180,000 mL/24 hours, most fluid reabsorbed
• Glomerulonephritis


  Protein in urine and edema
• Shock


  Drops blood pressure, decreases pressure in glomerulus
• Renin


  Acts with angiotensinogen to form angiotensin II, maintains sodium/water balance and blood pressure by vasoconstricting efferent arteriole, stimulates aldosterone release
• Tubular reabsorption


  Substances transported out of filtrate and back into blood, primarily in proximal convoluted tubule
• Glucosuria


  Glucose in the urine, indicator of possible diabetes
• Tubular secretion


  Substances leave plasma and enter renal tubule, H and K ions usually added to filtrate
• Osmoregulation


  Kidneys regulate water balance, ADH regulates water reabsorption in collecting duct, aldosterone regulates sodium reabsorption
• 180 liters of blood filtered, producing 1-1.8 liters of urine daily
• Urine components


  95% water, urea, uric acid, amino acids, electrolytes
• ADH (antidiuretic hormone)


  Water retaining hormone, increases water reabsorption in collecting duct
• Aldosterone


  Hormone that stimulates additional sodium reabsorption from collecting duct, increases blood pressure
• Uric acid


  Product of nucleic acid catabolism, 10% excreted, can cause gout
• Urea


  Product of amino acid catabolism, 50% reabsorbed
• Polyuria


  Excess urine production, >2.5 liters/day
• Oliguria


  Scanty urine production, <500 mL/day
• Anuria


  Absence of urine production, <70 mL/day
• Kidney stones


  Composed of uric acid, calcium, or magnesium, can cause pain from ureter stretching
• Cystitis


  Bladder infection, more common in females