Urinary system

• Urinary system


  Major organs and their generalized function
• Formation of urine


  1. Filtration

  2. Reabsorption

  3. Secretion
• Nephron


  Parts and role of each component in urine formation
• 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
• Urine formation


  1. Glomerular filtration

  2. Tubular reabsorption

  3. Tubular secretion
• Nephrons


  Juxtamedullary and cortical
• Glomerular filtration


  Capillaries of the glomerulus are fenestrated, allowing water and solutes to leave but not blood cells and plasma proteins
• Glomerular filtration rate (GFR)


  Volume of filtrate produced by both kidneys each minute, 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 that is still too much filtrate
• Descending limb of Loop of Henle

  An additional 20% of water is reabsorbed
• Collecting duct


  Last stop in urine formation, impermeable to NaCl but permeable to water
• ADH (antidiuretic hormone)


  Decreases the amount of urine by making the 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
• Abnormalities of urine volume

  Anuria, Oliguria, Polyuria
• Tubular secretion


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


  Considered the gold standard for measuring GFR, as inulin is freely filtered, not secreted or reabsorbed, and not synthetized or metabolized by the kidney
• Juxtaglomerular apparatus


  Specialized structure formed by the distal convoluted tubule and the glomerular afferent arteriole, regulates blood pressure and filtration rate
• Homeostasis 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+, making urine acidic
• Urinalysis


  Examination of urine to detect signs of disease through changes in normal characteristics or appearance of abnormal characteristics
• Ureters


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


  Elastic muscular organ capable of great expansion, stores urine before voiding
• Urethra


  Narrow tube from urinary bladder to exterior, passage of urine and male reproductive fluid
• Micturition


  Passage of urine from body, involving regulatory sphincters and bladder wall contraction
• Urinary retention, suppression, and incontinence


  Abnormalities in urine elimination