Excretory System Regulation of

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					 Regulation of Extracellular Fluids
• Excretory systems:
The removal from the body of the waste
  products of metabolic pathways
Osmoregulation – control of the water
  balance of the blood, tissue or cytoplasm
  of a living organism.
• Excretion applies to metabolic waste
  products that cross a plasma membrane.
• What are some wastes?
• Elimination is the removal of feces.
          Nitrogen Wastes
• Nitrogen wastes are a by product of
  protein metabolism.
• The NH2 (amino group) combines with a
  hydrogen ion (proton) to form ammonia
• Ammonia is very toxic and usually is
  excreted directly by marine animals.
  Terrestrial animals usually need to
  conserve water.
• Ammonia is converted to urea, a
  compound the body can tolerate at higher
  concentrations than ammonia.
• Birds and insects secrete uric acid that
  they make through large energy
  expenditure but little water loss.
• Amphibians and mammals secrete urea
  that they form in their liver. Amino groups
  are turned into ammonia, which in turn is
  converted to urea, dumped into the blood
  and concentrated by the kidneys.
• Terrestrial animals use a variety of
  methods to reduce water loss: living in
  moist environments, developing
  impermeable body coverings, production
  of more concentrated urine.
• Water loss can be considerable: a person
  in a 100 degree F temperature loses 1 liter
  of water per hour.
Vertebrates Have Paired Kidneys p
• The urinary system is
  made-up of the
  kidneys, ureters,
  bladder, and urethra.
• You must be able to draw kidney,
  nephron, and glomerulus… go to study
  guide p 101
  Structure of the Kidney p 101
Renal capsule: a thin
 outer membrane
Cortex: lightly colored
 outer region
Medulla: darker inner
Renal pelvis: funnel
 shaped cavity collects
Renal artery and vein
            Nephron p101
• The functional unit of the excretory system
  or urinary system
• The nephron is a long thin tube
• closed at one end
• two twisted regions interspaced with a
  long hair pin loop
• ends in a long straight portion and is
  surrounded by capillaries
• Nephrons filter 125 ml of body fluid per
  minute; filtering the entire body fluid
  component 16 times each day.
• In a 24 hour period nephrons produce 180
  liters of filtrate, of which 178.5 liters are
  reabsorbed. The remaining 1.5 liters forms
 The nephron has three functions:
1. Glomerular filtration of water and solutes
   from the blood.
2. Tubular reabsorption of water and
   conserved molecules back into the
3.Tubular secretion of ions and other waste
   products from surrounding capillaries into
   the distal tubule.
• Nephron anatomy
• Concentrating Urine - The Mammalian
• Animations and Tutorials
  The steps in urine production or
• Blood enters the glomerulus under
• This causes water, small molecules (but
  not macromolecules like proteins) and ions
  to filter through the capillary walls into the
  Bowman's capsule.
• This fluid is called nephric filtrate.
• Nephric filtrate collects within the
  Bowman's capsule and then flows into the
  proximal tubule.
• Here all of the glucose, and amino acids,
  reabsorbed by active transport.
• large volume of the water follows them by
  osmosis (80–85% of the 180 liters
  deposited in the Bowman's capsules in 24
• As the fluid flows into the descending
  segment of the loop of Henle, water
  continues to leave by osmosis because
  the interstitial fluid is very hypertonic.
• This is caused by the active transport of
  Na+ out of the tubular fluid as it moves up
  the ascending segment of the loop of
• In the distal tubules, more sodium is
  reclaimed by active transport, and still
  more water follows by osmosis.
• Final adjustment of the sodium and water
  content of the body occurs in the
  collecting tubules. (ADH)
• Read this explanation of the process:
  The Kidney
   Regulating Blood Composition

.concentrations of various ions and other
  important substances constant.
.volume of water in your body constant.
. acid/base concentration of your blood
. Removing wastes from your body.
• The kidney does this by a combination of three
• It filters 20 percent of the plasma and non-cell
  elements from the blood into the inside of the
  nephron (the lumen).
• It reabsorbs the components that the body
  needs from the lumen back into the blood.
• It secretes some unwanted components from
  the blood into the lumen of the nephron.
• glomerulus, blood plasma (the fluid
  component of blood) is forced out of the
  capillaries and into the nephron.
• Narrow spaces : proteins and RBC left
Note permeability
• Nephric filtrate
  collects within
   the Bowman's
  capsule and then
  flows into the
  proximal tubule.
• glucose, and amino acids, are
  reabsorbed by active transport.
• Filtrate must now travel through a long and
  winding tubular pathway, first through the
  cortex, or outer portion of the kidney, then
  the medulla, the deep portion.
• What happens to some of the substances which
  travel down the tubule.
• Pay attention to glucose, water, and salts. You
  need to know which is reabsorbed where, and
  which requires active transport.
• http://www.biologymad.com/resources/kidney.sw
• Concentrating Urine - The Mammalian Kidney
     Two major factors influence
• High concentration = more absorption …
  up to a limit . There are only so many
  transporters for each molecule and they
  can only carry so many at a time
• Rate of flow of the filtrate meaning that if
  the flow is quick there will be less
• The hypertonic interstitial fluid surrounding the
  tubules provides a high osmotic pressure for the
  removal of water.
• Transmembrane channels made of a protein
  called aquaporin are inserted in the plasma
  membrane greatly increasing its permeability to
  water. (When open, an aquaporin channel
  allows 3 billion molecules of water to pass
  through each second.)
• Insertion of these water channels requires
  signaling by the antidiuretic hormone
  (ADH; also known as arginine
• Animation: Hormonal Communication
• The Mammalian Kidney
Water control
• Virtual Anatomy Lab

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