Excretion in Humans

Cards (37)

  • Excretion is the removal of metabolic waste from the body
  • Metabolic waste is any waste that has been made from a chemical reaction
    e.g. carbon dioxide from respiration
  • What are the three organs of excretion?
    Kidneys, Skin & Lungs
  • The kidneys removes urea, water and ions from the blood. This is called urine.
  • The skin removes water and salt by sweating.
  • The lungs remove carbon dioxide and water from the blood when we breath out.
  • Proteins contain nitrogen. This means it needs to be excreted from the body as an excess amount is toxic.
  • The amino acids from the protein are first broken down in the liver.
    They are turned into a carbohydrate and urea.
    Urea passes into the blood and travels to the kidney to be excreted.​
  • The renal artery carries (unfiltered) blood from the aorta to the kidneys.
  • The renal vein carries filtered blood from the kidneys to the vena cava
  • The urine that is formed in the kidneys passes out through the ureters and is stored in the bladder.​
  • The kidney cleans/filters the blood and sends it back
  • Kidney is divided into two sections. Outer cortex and inner medulla.
  • The medulla is made up of about 30 pyramids.​
  • Nephrons are the functional units of the kidney. They filter the blood and produce urine. There are about one million nephrons per kidney.​
  • Define the term excretion (3 marks)
    Removal of poisons/toxins/harmful substances
    Removal of excess substances
    Removing waste products of chemical reactions in cells
    Metabolism, Respiration, Deamination

    For example the removal of CO2 after respiration.
  • State an excretory product that is passed out through the lungs.
    Carbon Dioxide or Water (vapour)
  • Role of the liver in excretion (3 marks)
    Deamination of amino acids
    Removal of nitrogen to produce urea
    Breakdown of toxins/extra vitamins
    Excretory products put in bile eg. cholesterol
  • Nephron journey:
    Blood
    Comes along a capillary which forms a bundle called the glomerulus
    Glomerulus -> Bowman's capsule -> Ultrafiltration -> Glomerular filtrate
    Useful products from the glomerular filtrate move back into the blood
  • Selective reabsorption - useful products moving back to the blood
    This occurs mainly in the Proximal Convoluted Tubule
    (useful product- glucose)
  • Selective reabsorption of water back into the blood happens in the loop of Henle​.
  • Glomerulus --> Bowman's capsule --> Proximal convoluted tubule --> Loop of Henle --> Distal convoluted tubule --> Collecting duct
  • Osmoregulation: The body can control water content of the blood using the kidney
  • Special cells in the hypothalamus of the brain detect the amount of water in the blood and they can then cause the pituitary gland to release a hormone called ADH.
  • What does ADH stand for? Anti-diuretic hormone
  • ADH travels to the kidney making the collecting duct walls more permeable therefore more water can be absorbed back into the blood.
  • Which part of the kidney does osmoregulation occur? Nephron
  • A runner is training hard on a hot day. Suggest how this could affect his urine. (5 marks)
    He is losing water through sweat (1) and respiration in the lungs (1). This is detected by the hypothalamus in the brain (1) which stimulates the pituitary gland (1) sending more ADH to the kidneys (1). The ADH will make the collecting ducts in the nephron more permeable (1) so more water is reabsorbed into the blood making his urine more concentrated (1).
  • Name the fluid that travels from the kidneys to the bladder: Urine
  • Describe the function of the bladder: stores urine and empties it into the urethra
  • How is urea produced?
    Urea is formed by deamination in the liver, removing the nitrogen containing part of excess amino acids to form urea.
  • Two waste substances that are removed from the blood by dialysis: urea/creatinine/uric acid/ammonia... (nitrogen, hormones)
  • One advantage and disadvantage of kidney transplant: Adv: there's no need to return to clinics for dialysis/patients can eat normally Dis: there's a risk of rejection/infection/death
  • Define active transport (2 marks)
    The movement of ions/large molecules through the cell membrane using energy from respiration.
  • Explain how a dialysis machine filters blood (4 marks)
    Minerals/salts/ions/urea is moved by diffusion (1) from high concentration to low concentration/down a concentration gradient (1) water moves by osmosis (1) glucose is not removed/same concentration (1) fresh dialysate maintains a concentration gradient (1).
  • Describe the function of the nephron:
    Filtration of blood and glucose, reabsorption of water and ions, and secretion of urea
  • What is mutation?

    A change in the DNA sequence of an organism. Mutation can be caused by mistakes during cell division.