excretion

• Excretion


  The process by which organisms eliminate waste products and maintain balance in their internal environment
• Excretion


  • Removal of metabolic waste products such as urea, uric acid, and carbon dioxide
  • In humans, the kidneys remove urea from the bloodstream
  • Solid waste is expelled from the large intestine
  • Helps regulate ionic concentration, water content, and pH of body fluids
• Excretion is an essential process in all forms of life
• In one celled organisms, waste are discharged through the surface of the cell
• Excretion removes unwanted by-products of metabolism, toxic chemical substances, regulates the ionic concentration of body fluids, regulates water content of body, regulates pH of body fluids
• Excretion


  Removal of toxic materials and waste products of metabolism from an organism
• Excretory Products


  • CO₂
  • Urea
  • Water
  • Excess heat
  • Bile pigments
• CO₂


  Produced during respiration, removed by lungs in expired air
• Urea


  Produced during deamination of excess amino acids in the liver, excreted mainly by the kidneys in urine
• Water


  Produced during respiration in body cells, from diet
• Bile pigments


  Produced during breakdown of old red blood cells in liver, excreted in urine and by skin in sweats
• Removal of CO₂ from lungs

  1. CO₂ is produced during respiration

  2. Diffuses from body cells into blood plasma

  3. Carried in the form of hydrogen carbonate ions into the lungs

  4. Converted back in blood capillaries

  5. Diffuses into alveoli

  6. Removed in exhaled air
• Role of Liver in Deamination

  1. Amino acids are broken down in liver

  2. Nitrogen-containing part is removed to form urea

  3. Urea diffuses from liver cells into blood plasma

  4. Carried to kidneys where it is excreted in urine
• Liver is the site where amino acids are used to make plasma proteins
• Function of Liver


  Assimilation of amino acids by converting them to proteins<|>Deamination: removal of the nitrogen-containing part of amino acids to form urea<|>Alcohol, drugs & hormones are broken down in the liver
• Assimilation


  The uptake and use of nutrients by cells
• Function of Kidney


  Removal of urea and excess water<|>Re-absorption of glucose and some salts
• Kidney structure


  • Cortex
  • Medulla
  • Renal Artery
  • Renal Vein
  • Pyramid
  • Pelvis
• Left kidney is higher than the right one
• Bladder


  Stores urine
• Renal artery


  Brings wastes and water from the blood
• Renal vein


  Reabsorbs water and functional molecules and leaves wastes behind
• Blood that enters the kidneys along the renal artery has a higher concentration of urea
• Blood that leaves the kidneys along the renal vein has a lower concentration of urea
• Kidneys


  Excretory organs that remove nitrogenous wastes and other toxic substances from blood
• Kidneys


  Osmoregulatory organs that maintain a constant water potential of blood and tissue fluids
• If water content of blood is too high


  Excess is removed in urine
• If water content of blood is too low


  It is retained in the body
• Structure and Function of the Nephron

  1. Ultrafiltration

  2. Selective reabsorption

  3. Loop of Henlé

  4. Collecting duct
• Ultrafiltration


  1. Blood from the renal artery enters the glomerulus

  2. Water, urea, salts and glucose are forced into the Bowman's capsule

  3. Blood cells and large proteins cannot pass through
• Selective reabsorption


  1. Two-thirds of the salt and water and all the glucose move out of the nephron by active transport

  2. These substances are reabsorbed back into the blood capillary
• Loop of Henlé


  1. Part is permeable to water but not salt

  2. Water is drawn out of the filtrate in the nephron by osmosis
• Collecting duct


  Remaining substances move into the collecting duct, forming urine
• Bowman's capsule


  Cup-shaped structure containing a mass of blood capillaries, acts as a filtration unit
• Proximal Tubule


  Twisted region concerned mainly with selective reabsorption
• Loop of Henlé


  Long hair-pin loop involved in reabsorption of water by osmosis
• Distal coiled tubule


  Second twisted region concerned with osmoregulation
• Collecting duct


  Tube into which several second coiled tubules empty their contents (urine) and which leads into renal pelvis
• Filtration of blood


  1. Separation of small molecules in blood from larger ones

  2. Blood vessel leaving glomerulus is narrower than that entering it

  3. This decrease in diameter creates a high blood pressure that forces out of blood into lumen of Bowman's capsule
• Selective reabsorption


  Useful substances like glucose, amino acids, and vitamins are reabsorbed into the blood