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BIOLOGY · Stage 9 · Chapter 10: Excretion in Humans

Biology 10.2 The human excretory system — Kidneys, Ureters, Bladder and Urethra

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10.2 The human excretory system — Kidneys, Ureters, Bladder and Urethra — Alhussan International Academy — Biology (Stages 7–9) notes: Name and locate the parts of the human excretory (renal) system, describe their functions and outline how urine is made and stored.Human excretor…

  • Human excretory system (renal system)
  • Renal artery
  • Renal vein
  • Blood flow
  • Rich blood supply
  • Filtration

Section 1 of 5The urinary system

  • Human excretory system (renal system)
    • it removes urea and controls water balance, and urine flows through its parts in a set order.
  • Kidneys
    • two organs at the back of the abdomen, protected by the lower ribs, which filter the blood and make urine.
  • Ureters
    • two narrow tubes that carry urine from the kidneys to the bladder by waves of muscle contraction.
  • Bladder
    • a muscular, stretchy bag that stores urine and is emptied when it is full.
  • Urethra
    • the tube through which urine leaves the body, with a ring of muscle (sphincter) controlling release.

Section 2 of 5Blood supply and kidney structure

  • Renal artery
    • it brings blood containing urea from the liver to the kidney.
  • Renal vein
    • it carries away blood with much less urea.
  • Blood flow
    • kidneys receive about one fifth of the blood pumped by the heart, which shows how important their work is.
  • Regions
    • the cortex is where filtration takes place, the medulla is where water is reabsorbed, and the pelvis collects urine and leads to the ureter.

Section 3 of 5How the kidneys make urine

  • Rich blood supply
    • the blood entering carries dissolved food molecules, oxygen, salt, urea and many other substances.
  • Filtration
    • water, glucose, salts and urea pass out of the blood at the glomerulus.
    • Blood cells and big molecules the body needs stay in the blood.
  • Selective reabsorption
    • useful small molecules, including all the glucose, most of the water and the salts the body needs, are taken back into the blood in the tubule.
  • Urine
    • the remaining liquid, containing urea, excess water and salts, passes to the collecting duct as the yellow liquid urine.
  • Volume
    • an average adult produces about 1500 cm3 of urine every day.

Section 4 of 5Controlling water balance

  • Large drink
    • the kidneys filter a lot of water out of the blood, so lots of very dilute urine is produced.
  • Little drink, hot weather or exercise
    • the kidneys save water to keep the blood at the right concentration, so a small volume of concentrated, darker urine is produced.
  • ADH
    • the hormone ADH, released from the pituitary gland in response to blood concentration, adjusts how much water is reabsorbed.
  • Urine colour
    • it varies from very pale to deep yellow, and pale yellow usually means the body is well hydrated.

Section 5 of 5Urine composition and health

SubstanceIn blood entering kidneyIn urine
UreaPresentHigher concentration
GlucosePresentNone (in a healthy person)
ProteinPresentNone
WaterPresentVaries with need
  • Urine tests
    • doctors check urine samples to make sure patients have healthy kidneys.
    • Glucose in urine suggests diabetes.
    • Protein in urine suggests kidney damage.

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