the kidneys

• kidneys are the major organ of excretion and osmoregulation.
• location of kidneys: below the diaphragm in the small of the back. in the depression known as the hilium
• • the urinary system consists of the kidneys, bladder and ducts (tubes)
  • kidneys excrete urea and water salts in the form of urine
• the kidneys work by:

  1. filtering the blood
  2. absorbing back what the body needs to keep
  3. the wastes pass from the bladder for storage and release. as urine is produced it flows into the renal pelvis, then into the ureter and to the bladder
• renal = to do with the kidneys
• in the kidney, urine is formed at the nephron. the nephron is a filtration unit located in the cortex and medulla of the kidney.
• Filtration

  Occurs in the outer cortex
• Substances: glucose, amino acids, water, urea and salts filter out of the blood into narrow tubules
• Reabsorption

  Occurs in the cortex and Medulla
• Reabsorption

  Blood vessels reabsorb back useful nutrients from the tubules
• Reabsorption

  Urea, excess salts and water, are allowed to continue down the tubule and on to the bladder
• Secretion

  The production and release of chemicals from cells
• Secretion

  Some substances, potassium and hydrogen ions, are secreted from the blood into the tubule in the cortex
• Blood becomes too acidic

  Hydrogen ions are secreted into the urine
• Kidneys

  Control blood pH by controlling the hydrogen ion concentration in the blood
• Bladder

  Stores the urine, which flows through the urethra to the outside
• Urine

  Composed of about 96% water, urea, salt, and traces of other substances such as hormones