Excretory System
Ashley Donato
Excretory System
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Excretion is a the process in which the organism rids
itself of metabolic wastes.
Elimination of fecal material is not part of the
excretory system because fecal material stays in the
intestine which is not in the body proper.
In humans the metabolic waste comes from urine,
sweat and tears.
Excretory System
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Only waste material from metabolic activities are
excretory products
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CO2 is a major excretory product as well as nitrogen
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CO2 arises from the breakdown of organic fuel
molecules. Some CO2 is used for synthetic
reactions, but most is excreted from the body.
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Excretory System
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When protein is used as a fuel the amino acids are
broken down and the nitrogen is removed.
Nitrogen can be excreted out of the body in 3 forms
as ammonia, urea, or uric acid.
The availability of water determines how the
nitrogen will be excreted.
Excretory System
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Commonly aquatic organisms can excrete ammonia
because water is more freely available to them.
For nonaquatic organisms ammonia is toxic and
usually needs to be neutralized into urea.
Humans are ureotelic which mean they excrete
nitrogen as urea.
Excretory System
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Ureotelic organisms produce uric acid which is non
toxic. It’s relatively insoluble in water and less fluid is
needed to get rid of it, but there is a higher energy
cost to form it.
This process takes place in the liver and the filtrate is
brought to the kidneys and excreted as urine.
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Excretory system of Invertebrates
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Protista and sponges excrete wastes by a contractile
vacuole.
Contractile vacuole is full of fluid and it contracts to
force fluid, salts and waste material out of the cell.
Some protists lack the vacuole and excrete their
waste across the permeable cell membrane.
Excretory system of Invertebrates
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Flatworms use the flame cell system.
Which is two highly branched tubules with hollow
bulbs on the ends with cilia. The beating cilia make it
look like a flame.
The cilia create a current that carries the fluid and
waste material out of the body through the excretory
pores.
Flame cell system
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Excretory system of earthworms
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Earthworms have a pair of nephridia on each
segmented part of their body.
Fluid enters a nephridium through the nephrostome
The nephridium moves the waste into a bladder and
then it exits through the nephridiopore.
Excretory system of earthworms
Excretory system of insects
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Insects have
Malpighian tubules
which are
outpocketings located
at the joint of the
midgut and hindgut.
These are tubular sacs
that collect the waste
material at the closed
ends.
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Excretory system of insects
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Insects form uric acid in
the tubules and water
and salts are
reabsorbed.
The urine formed is
moved to the hindgut
and excreted out of the
body.
Vertebrate Kidney Structure
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Kidneys are unique organs to vertebrates.
They function as the excretory organ in most
vertebrates and in fish the main function is
osmoregulation.
Kidney ducts and the reproductive system are
interrelated because they often share the same
external opening.
Vertebrate Kidney Structure
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Kidney development starts off as series of tubules
that are associated with segments of the body.
The tubules lengthen and become nonsegmented.
The nonsegmented tubules form a duct called the
ureter.
The ureter moves the urine formed in the kidneys to
the urinary bladder.
The urethra moves the urine from the bladder to
outside the body.
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Vertebrate Kidney Structure
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The kidney has 3
sections
Outer cortex
Middle medulla
Center pelvis.
Urine collects in the
renal pelvis and is
moved to the bladder
by the ureter.
Vertebrate Kidney Structure
Vertebrate Kidney Structure
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The nephron produces
the urine.
The nephron has 3
parts
Glomerulus
Convoluted tubule
Collecting tubule
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Vertebrate Kidney Structure
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The glomerulus
consists of tightly
packed capillaries that
filter the blood
Small particles and
salts are filtered out,
but larger particles such
as proteins are left in
the blood
Vertebrate Kidney Structure
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The filtrate is then
passed to the
convoluted tubule,
The convoluted tubule
consists of the
Bowman’s capsule, the
proximal section, loop
of Henle and the distal
section
Vertebrate Kidney Structure
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In the convoluted tubule water and ions are
reabsorbed and put back into the bloodstream
Urine is passed on to the collecting tubule.
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Vertebrate Kidney Structure
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In the collecting tubule more water is reabsorbed if
possible
The urine is moved from the collecting tubule to the
pelvis of the kidney.
Vertebrate Kidney Structure
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The glomerulus, Bowman’s
capsule, proximal and distal
sections are located in the
cortex of the kidney.
The loop of Henle and
collecting tubules are in the
medulla.
Human Kidney Function
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Human kidneys are able to produce very
concentrated urine due to a steep concentration
gradient in the renal medulla.
Hypoosmotic urine passes from the descending arm
of the loop of Henle into the collecting tubule.
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Countercurrent multiplier theory
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Na+ and Cl- circulate from the ascending arm to the
descending arm of the loop of Henle.
This occurs by filtrate descending the loop of Henle
and water passing by osmosis into the tissue fluid
and around the tubule.
Na+ and Cl- diffuse into the tubule at the same time
that the water is passing into the tissues.
Countercurrent multiplier system
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The ascending arm of the loop actively expels Na+
and Cl- expels passively.
This repeating filtration process produces highly
concentrated urine
This theory had been doubted and the new
hypothesis is the two-solute model
Two-solute model
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The filtrate fluid is initially isotonic with blood plasma
The filtrate moves down the descending arm and
loses water and becomes concentrated.
At the bottom of the loop the tubule is permeable to
NaCl .
As the filtrate moves up the ascending arm salt is
actively pumped out as well as additional water loss.
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Two-solute model
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The filtrate is brought to the collecting ducts which
are permeable to urea.
The urea passes out of the ducts and into the
surrounding tissues.
The salt and urea pull more water from the filtrate as
it moves from the capsule to the ureter.
Fresh water fish
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Kidney function in fresh water fish is very important
because they have to conserve salts and excrete out
lots of fluid, they produce large amounts of urine and
fairly quickly
Fluids are pushed across the vessel membrane in
the glomerulus, then the neck of the Bowman’s
capsule is highly ciliated so that large amounts of
water can move through the nephron.
Fresh water fish
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Ions such as Na+, K+
and Cl- are reabsorbed
using active transport.
Urine is formed and
moved to the urinary
bladder and then
released into the water.
Fish excrete out
ammonia through their
urine and it passes
through their gills
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Marine fish
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Produce urine more
slowly because they
have to reabsorb fresh
water from the filtrate.
Marine fish drink the
salt water to counter
balance their loss of
water to their
hypertonic
environment.
Homeostasis
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The kidneys also help maintain homeostasis by
regulating the salt and water balance.
The kidneys control the solutes that get reabsorbed
back into the bloodstream after they get filtered in
the tubules
Homeostasis
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Glucose is a solute that is usually entirely
reabsorbed.
In diabetics the glucose does not get reabsorbed
and they have high levels of glucose that they
excrete out in their urine.
When the body is losing glucose through urine more
water is drawn into the nephron and large amounts
of urine is produced.
Frequent urination can be one of the first signs of
diabetes.
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Homeostasis
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Antidiuretic hormone (ADH) is produced in the
hypothalamus and it functions to maintain water
balance.
ADH helps the body to retain water and produce
concentrated urine.
Low levels of ADH produces large amounts of dilute
urine taking water out of the body.
Homeostasis
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Aldosterone is a steroid produced in the adrenal
cortex that regulates active transport of Na+.
It helps to retain salts in the body.
With low levels of this steroid salts are lost from the
body.
Sweating
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Sweating can also be a
excretion process.
Sweat glands in the
skin are also ways that
the body can lose water
and salts such as NaCl,
K+ and Mg²+.
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Tears
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Tears which function to
moisten the eye are
also part of the
excretory process.
Tears are dilute NaCl
solutions.
Sources
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Fried, George and Hademenos, George.
Schaum’s Outline to Biology. New York:
McGraw Hill. 2009.
www.google.com/images
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