L1 - Human Excretory System

• Blood enters the kidney through the renal artery.
• Blood exits the kidney through the renal vein.
• The ureter is a tube that carries urine from the kidney to the bladder.
• The bladder stores urine.
• The urethra carries urine from the bladder out of the body.
• The kidneys regulate the water content of the blood using ADH (osmoregulation) and remove waste products/urea from it (excretion).
• The kidney removes urea, and excess salts and water.
• The solution of wastes is urine, and this drains from the kidneys down the ureters to the bladder, where it is stored until it can be eliminated from the body.
• Ultrafiltration:

  • There is a change in diameter of the blood vessel as it gets narrower in the capillary knot. This makes pressure in the capillary very high so that ultrafiltration can occur.
  • This means that small molecules like water, urea (poisonous waste), glucose and salts are filtered under pressure through the capillary knot into the Bowman's capsule
  • Big proteins and blood cells are too big to pass through the capillary wall. They stay in the blood.
• Selective reabsorption:

  • Selective reabsorption of ALL glucose, some salts and much of the water takes place in the tubule so that these useful molecules, needed by the body, go back into the blood.
  • Urine is a mixture of urea, water and salt. It travels from the collecting duct to the ureter then onto the bladder where it is stored.
• Blood should never pass through the kidney and be present in urine.
• Blood contains cells, water, protein, glucose, salts and urea.
• Filtrate in tubule contains water, glucose, salts and urea.
• Urine contains water (dependent of reabsorption), salts (dependent of reabsorption) and urea.