EXCRETORY SYSTEM

• Organs involved in processing or excreting wastes

  • Lungs
  • Liver
  • Sweat glands in the skin
  • Alimentary canal
  • Kidneys
• Lungs


  Involved in the excretion of the carbon dioxide that is produced by all body cells during cellular respiration
• Liver


  Processes many substances so that they can be excreted
• Sweat glands in the skin

  Secrete sweat, which is largely water, for cooling
• Alimentary canal


  Passes out bile pigments, which enter the small intestine with the bile
• Kidneys


  Principal excretory organs, responsible for maintaining the constant concentration of materials in the body fluids
• Liver


  • Located in the upper abdominal cavity
  • Very large organ with a host of different functions, one of which is the preparation of materials for excretion
• Deamination


  1. Enzymes remove the amino group (NH2) from the amino acids

  2. Liver cells convert ammonia (NH3) to urea

  3. Remaining part of the amino acid is converted into a carbohydrate that can be readily broken down by the cells to release energy, carbon dioxide and water
• Other functions of the liver

  • Detoxifies alcohol and other drugs
  • Deactivates many hormones and converts them into a form that can be excreted by the liver
  • Breaks down haemoglobin from dead red blood cells to produce bile pigments, which are then passed out of the body with the faeces
• Skin


  • Provides a protective covering over the surface of the body
  • Regulates body temperature
  • Has an important role in excretion
• Sweat glands


  Secrete about 500 mL of water per day, containing dissolved sodium chloride, lactic acid and urea
• Sweat secretion


  1. Sweat glands located in the lower layers of the skin

  2. Duct carries the sweat to a hair follicle or to the skin surface where it opens at a pore

  3. Cells surrounding the glands are able to contract and squeeze the sweat to the skin surface
• Kidneys


  • Located in the abdomen
  • Each kidney is approximately 11 cm long
  • Kidneys, bladder and their associated ducts make up the urinary system
• Structure of kidneys


  1. Renal capsule

  2. Outer renal cortex

  3. Inner renal medulla

  4. Renal pelvis

  5. Renal hilum
• Nephrons


  • Functional unit of the kidney, where urine is formed
  • About 1.2 million nephrons in each human kidney
  • Each nephron surrounded by a complex network of blood capillaries
• Production of urine


  1. Glomerular filtration

  2. Selective reabsorption

  3. Tubular secretion
• Glomerular filtration


  Fluid is forced out of the blood and collected by the glomerular capsule
• Selective reabsorption


  Components of the plasma that are filtered from the capillaries of the glomerulus are reabsorbed into the blood in the peritubular capillaries
• Tubular secretion


  Adds materials to the filtrate from the blood, such as potassium, hydrogen ions and creatinine, to maintain blood pH and urine pH
• Urine drainage


  1. Water and other substances not reabsorbed drain from the collecting ducts into the renal pelvis

  2. Urine drains into the ureters and is pushed to the urinary bladder where it is stored

  3. Urethra carries urine from the bladder to the exterior of the body
• Composition of urine


  Normal urine is a solution of water with dissolved wastes, such as urea and creatinine, and ions such as sodium, chloride and potassium, as well as low levels of other solutes
• A healthy adult produces about 1.5 L of urine a day, but this varies depending on diet, environment and other factors
• Kidney stones


  Formed from solid crystals that build up inside the kidneys, usually when urine becomes too concentrated
• Small crystals may pass unnoticed, or crystals may combine to form stones. Large stones can get stuck in the ureter, bladder or urethra, causing intense pain, and may need to be broken up with sound waves or physically removed during surgery
• Kidney failure


  Occurs when the kidneys lose their ability to excrete waste and to control the level of fluid in the body
• Causes of kidney failure

  • Diabetes
  • High blood pressure
  • Kidney diseases that slowly destroy the nephrons in the kidneys
• The only way to maintain life with kidney failure is by dialysis or a kidney transplant
• Lifestyle measures to maintain healthy kidneys

  • Maintain a healthy diet and weight
  • Abstain from smoking
  • Drink water instead of sugary drinks
  • Drink alcohol in moderation
  • Do not use performance-enhancing drugs
• Liver disease


  Occurs when the liver is not able to function effectively and is unable to process toxins ready for elimination
• Causes of liver disease

  • Infection
  • Autoimmune problems
  • Genetic disorders
  • Cancer
  • Lifestyle factors such as excessive alcohol consumption and a fatty diet
• Symptoms of liver disease

  • Yellow tinge to the skin (jaundice)
  • Abdominal pain and swelling
  • Swelling in the legs and feet
  • Nausea or vomiting
  • Fatigue
  • Dark urine
  • Pale or dark coloured faeces