- 1. What is Excretion? Excretion is the process of removing cellularwastes. The term excretion refers specifically to theelimination of wastes produced by cellular activity. It is not removal of undigested food material! Goal: Maintain homeostasis!!
2. What is Excretion? (contd) The most important waste products are CO2,nitrogen compounds, and salts. CO2 produced during cellular respiration(in addition to water) Nitrogen compounds (ammonia, urea, anduric acid) produced by the breakdown ofamino acids (protein digestion) Salts produced by metabolism 3. Why do we need to excrete Ammonia? All organisms produce ammonia as theymetabolize nutrients (protein digestion) Ammonia is a nitrogenous waste that is toxicand must be removed from the body How an organism removes ammonia dependsupon where it lives 4. Removing NitrogenousWaste Products(1) Ammonia (NH3):-Requires little energy-Ammonia is highly toxic!-This form of waste can only be used ifthe organism lives in an aquaticenvironment-Example: Paramecium, protists, someocean fish. 5. Removing Nitrogenous Waste Products(2) Urea:- Many land animals and somebony fish (amphibians,mammals) dilute the toxicammonia with water.- This substance is called Urea & isfiltered out by the kidneys.- The problem is they do losewater in the process!- Requires Energy 6. Removing Nitrogenous Waste Products(3) Uric Acid Not very toxic becauseinsoluble Evolved as an adaptation ofland animals Many organisms try toconserve water & excrete theirNitrogen waste as a solid!(little loss of water is involved) Examples: insects, reptiles,birds 7. The Mystery behind Bird Poop Unlike mammals, birds do not urinate. Their kidneys extract nitrogenous wastes from thebloodstream, and excrete it in the form of uric acid. Uric acid has a very low solubility in water, so itemerges as a white paste. 8. Human ExcretionWhere does excretion occur in humans?Like other animals humans have a systemthat excretes Nitrogen wastes as Urea, salt, and waterUrinary System: Kidneys, ureter, urethra, and bladderKidneys (located in back) play important role in homeostasis - remove waste products from blood- maintain blood pH- control water content of blood 9. How The Kidneys Work1) Blood enters kidneys fromrenal artery2) Blood is filtered by passingthrough millions ofnephrons3) Wastes pass through ureterto the bladder as urine4) Clean blood returns tobody through renal vein5) Bladder stores urine andpasses urine out of thebody through the urethra 10. Nephrons: How the Body makes Urine Your kidneys arecomposed of 1 millioncells called Nephrons. These long coiledtubes are where theblood is actuallyfiltered and urine isproduced 11. The Nephron Nephron has threefunctions:1. Glomerular filtration: filterout water, N-wastes (urea),salt, glucose, amino acids2. Tubular reabsorption:reabsorb materials that thebody still needs (foodmolecules, water).3. Tubular secretion: collectwastes as urine and passthem to the bladder (urea,salts, other substances)Blood filters through thekidneys about 6 times a day.99% of the water isreabsorbed and not excreted 12. Anatomy of 1 Nephron 13. Anatomy of 1 Nephron 14. What kinds of animals have the mostefficient kidneys? Desert animals must beable to conserve moisture Most terrestrial animalsmust drink fresh wateroften; however thekangaroo rat does notneed to drink water veryoften its kidneys absorbevery little drop of water 15. Kidney FailureIf renal failure occurs,people must get their blood filtered throughDialysis. 16. GoutIs a disease where the human body accumulates Uricacid in the joints. Heredity, alcohol & kidney failurelead to this problem.