Excretory System

• Nephron


  The functional unit of the kidney
• The glomerulus is a 'knot' of capillaries
• Capillaries are only 1 cell thick within the glomerulus
• The blood is under HIGH pressure within the glomerulus
• Ultrafiltration


  Small molecules and ions can pass through the membrane into the Bowman's capsule
• Selective Reabsorption

  The body is reabsorbing minerals and ions selectively
• Most of the reabsorption occurs in the PROXIMAL CONVOLUTED TUBULE
• ADH (Anti-diuretic hormone)


  Increases the amount of water and salts reabsorbed within the kidney
• ADH is released by the pituitary gland for OSMOREGULATION
• Loop of Henle


  • Has 2 main sections: Descending and Ascending
  • Where salt and water are reabsorbed
• Selective reabsorption

  • Water reabsorption
  • Salt reabsorption
• Descending limb


  Permeable to WATER, water leaves the nephron via OSMOSIS into the blood
• Osmoregulation


  The body's water content is controlled by the kidneys
• ADH (Anti-diuretic hormone)


  • Increases the amount of water and salts reabsorbed in the kidneys
  • Released from the pituitary gland to maintain homeostasis
• Ascending limb


  Permeable to ions such as NA+ (sodium/salt), these ions leave the nephron via DIFFUSION
• Urea

  • Birds convert nitrogenous waste into insoluble uric acid, which is nearly non-toxic
  • It uses more energy to make than urea
  • But it requires less water to produce, meaning that birds require less water in their body and are therefore lighter for flight
• • Cirrhosis is where scar tissue affects normal liver function
  • It cannot be reversed and can actually stop the liver from functioning, resulting in liver failure
  • This affects how well the liver converts ammonia into urea causing toxic chemicals to build up
  • Common causes of cirrhosis are: damage to the liver from disease, medication or toxins; infection of hepatitis C; excess fat build-up in the liver
• The amount of water reabsorbed depends on ADH
• The Distal convoluted tubule and Collecting Duct are parts of the nephron
• • There is no cure for cirrhosis, however, preventative treatment such as healthy diet, exercise and treatment of underlying conditions can help prevent it from getting worse
  • Symptoms/signs can vary depending on the cause, however they will often include: loss of appetite, weight loss, vomiting and/or diarrhoea, lack of energy, increase of urination
• Nephritis

  • Inflammation of the kidneys which leads to problems filtering the blood effectively
  • It can be caused by disease, medication or some disorders
  • Symptoms include: weight loss, protein in urine, increased thirst, increased urination and vomiting
• Helps to maintain a constant internal environment (A.K.A homeostasis)
• Main types of metabolic waste produced by animals

  • Water
  • Carbon dioxide (CO2)
  • Salts
  • Urea
• Excretory organs in the body

  • Lungs
  • Skin
  • Liver
  • Kidneys
• Lungs

  1. Carbon dioxide moves out of cells into bloodstream

  2. Carbon dioxide excreted when animal breathes out

  3. Cellular respiration produces carbon dioxide as waste
• Skin


  1. Sweat is made up of water, salts and urea

  2. Sweating performs cooling effect on body

  3. Sweating excretes metabolic wastes
• Liver

  1. Converts nutrients from food into substances body can use

  2. Breaks down toxic substances and converts them into harmless substances or ensures they are excreted
• Mammalian Urinary System is made up of: Two kidneys (which have a renal cortex and renal medulla each), Two tubes called ureters, A urinary bladder, A tube called a urethra
• Metabolic wastes taken from blood by kidneys


  • Water
  • Salts
  • Urea (uric acid in birds)
• Glomerulus


  Acts as a sieve to filter blood at high pressure
• Important parts of the nephron to remember

  • Glomerulus
  • Bowman's Capsule
  • Loop of Henle (Descending and Ascending)
  • Collecting Duct
• Excretion is the removal of metabolic waste from the body
• Types of metabolic waste produced by animals

  • Water
  • Carbon dioxide (CO2)
  • Salts
  • Urea
• Excretory organs


  • Lungs
  • Skin
  • Liver
  • Kidneys
• Skin excretion

  Sweat helps to cool you and gets rid of excess water and salts
• Sweat

  Made up of water, salts and urea
• Sweating

  • Cooling effect on the body
  • Excretes metabolic wastes
• Liver


  • Breaks down toxic substances and converts them into harmless substances or ensures they are excreted from the body
  • Converts ammonia into urea via the ornithine cycle
• Fish can excrete ammonia but mammals must first convert it to urea
• Kidney


  Removes urea and regulates the amount of salt and water in the body