Waste removal

1
Waste removal

• Aquatic organisms need to get rid of excess
  water and waste products
  (water tends to diffuse-in through osmosis) .
• Terrestrial organisms must get rid of waste
  products, but conserve and control water loss.
• Homeostasis balanced controlled conditions
  in internal environment of organisms. Needs to be
  maintained.
• 1- Unicellular organisms Vacuoles
  take out excess water and waste.
• 2- Simple multicellulars (sponges, Hydra)-
  excrete directly outside each cell.
• 3- Complex multicellulars- specific
  structures for water balance and waste
  removal

2
Waste materials

• Waste gases (CO2, O2), salts, water, nitrogenous
  wastes. Nitrogenous waste from foods is most
  problematic because it is highly toxic. Rest of
  waste products are not problematic (digestive
  system as feces)
• Ammonia (NH3) is produced from metabolism of
  nitrogen containing foods (proteins and nucleic
  acids).
• Toxicity Ammonia gtgt Urea gt uric acid
• - Aquatic organisms Ammonia is produced and
  flushed out into external water.
• - Most terrestrial organisms Ammonia is
  converted to Urea, which is released (diluted in
  some water). Some fish also excrete urea.
• - Desert animals and birds Ammonia is
  converted to Uric acid which is released as
  crystals, with almost no water loss.

3
Human Urinary System

• Goal Getting rid of nitrogenous waste and
  maintaining homeostasis.
• Urinary system Kidneys (organs for metabolic
  waste processing), blood vessels (veins,
  arteries, capillaries) various tubulae and
  holding structures.
• Each kidney contains a million nephrons, the
  actual operative units. Nephrons perform
  filtration, reabsorption and secretion.
• Nephrons contain glomerular capsules (Bowmans
  capsules).
• - Filtration In glomerulus
• - blood cells blood proteins retained in
  capillaries
• - the filtrate (materials that pass thru)
  includes plasma,
• N-waste, urea, salts, ions, glucose,
  aminoacids
• - Reabsorption (Recovery back to blood) In
  Tubule of the nephron.
• - Water by osmosis (99 of fluid arriving at
  nephron)
• - salt (Na, K) by active transport
• - glucose, aminoacids, some urea by active
  transport
• - Secretion Cells in Tubule of nephron remove
  substances left secrete them into the
  filtrate (excess K)

4
Human Urinary System

• ? Trajectory of nitrogenous waste
• 1- Renal artery carries dirty blood into
  kidneys and into nephrons
• 2- Nephrons (two tubes with a cup in the middle
  glomerular capsule). Dirty blood enters the
  nephron, goes thru mass of capillaries
  (glomerulus), and waste product leaves as urine
  through the other end, and clean blood leaves
  the nephron. Purified blood is collected from
  nephrons and leaves the kidney via renal vein.
• 2- Waste product (urine) from all nephrons is
  collected and drains thru the Ureter (tube) to
  urinary bladder (holding tank).
• 3- Urethra (tube) takes urine to exterior
  (urination)

5
Human urinary system - Control

• About 15 of processing of salt, water and other
  substances is under various types of control
  other than the kidneys.
• Feedback Regulation mechanisms Substances
  inhibit their own formation.
• 1- Excretion of some of Na and K- controlled by
  hormone aldosterone from adrenal glands, next to
  kidney.
• Feedback mechanism
• - too HIGH K ? aldosterone released into
  blood ? K secreted from blood into tubules ?
  lowers blood K/aldosterone levels
• 2- Water regulation Affects blood pressure
  volume. Controlled by Antidiuretic Hormone from
  pituitary gland.
• Feedback mechanism
• - Too low blood pressure/volume ? ADH released
  into blood ?collecting duct cell membranes more
  permeable ? more water into blood ? improved
  pressure/volume ? decrease in ADH level.