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Urinary and Excretory System

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									Urinary and Excretory System

     Likhitha Musunuru, Sal
  Ghodbane, and Margaret Strair
   Function of Excretory and Urinary Systems

•Physiological problem: maintaining a consistent
internal environment
•Excretory system in all types of organisms has one
main function: maintain homeostasis within a
given organism
  •Homeostasis- condition in which all internal
  systems and chemicals of that organism are in
  consistent balance
  •Involves the removal and gain of equal amounts
  of material
    Mechanisms of Homeostasis
• Homeostatic control systems have
  three components: receptor, control
  center, and effector
• Receptor detects a change in some
  variable of the animal internal
• Control center processes the
  information it receives from the
  receptor and directs a response by the
          Negative Feedback
• Negative feedback is when a change in
  the variable triggers the control
  mechanism to counteract further
  change in the same direction
• This prevents small changes from
  becoming too large
• Most homeostatic mechanisms
  including human temperature is
  regulated this way
             Positive Feedback

• Positive Feedback is when a change in a
  variable triggers mechanisms that amplify
  the change
• Childbirth occurs this way when pressure of
  a baby’s head pushes against the uterus
  triggering heightening of contractions which
  causes even greater pressure
   Means of Maintaining Homeostasis
 1. Rid organisms of waste products
 2. Keep both the fluid and the salt content of the
    organism within normal parameters
 3. Keep the concentration of other substances in
    body fluids at normal levels
Osmoregulation- how animals regulate solute
concentrations and balance the gain and loss of water
Excretion- how animals get rid of nitrogen containing
waste products of metabolism
            Review of Osmosis
All animals face the same problem of
osmoregulation: water uptake and loss
must balance
•Osmosis occurs when two solutions
separated by a membrane differ in osmotic
pressure or osmolarity
        How Osmosis is Controlled
An animal is a regulator if it uses internal
control mechanisms to moderate internal
change in the face of external fluctuation
-Example: Freshwater fish are able to
maintain stable internal concentration of
solutes in blood and interstitial fluid even
though that concentration is different from
the solute concentration of the water it lives
• Conformer is an animal
  that allows its internal
  condition to vary with
  certain external changes
• Example: Maine
  invertebrates such as
  spider crabs, live in
  environments with
  stable solute
  concentration. It
  conforms its internal
  solute concentration to
  the environment
             A Continuum
• Regulating and conforming are two
  extremes of a continuum
• No animal is a perfect regulator or
• Some animals regulate some
  internal conditions and allow
  others to conform
        Function of Osmoregulation
• Ultimate function of osmoregulation is
  to maintain cellular cytoplasm
  – Animals with open circulatory system
    (insects) manage the hemolymph, or fluid
    that bathes the cells
  – Animals with closed circulatory system
    (vertebrates), cells are bathed directly in
    interstitial fluid that is directly controlled by
    composition of the blood
       Solutions to Osmolarity
-Marine animals can be isoosomotic to
surroundings (osmoconformer)
      -Live in stable environments
-Osmoregulator is an animal that controls
its internal osmolarity
      --Animals in hypoosmotic
      environment must discharge water
      and vice versa
      --Allows animals to live in places
      conformers cannot like freshwater
      and terrestrial habitats
• Osmoregulators maintain the osmotic gradients
  that cause water to move in or out by using
  active transport.
• Energy cost of osmoregulation depends on how
  different an animal’s osmolarity is from its
  surrounds and how much work is required to
  pump solutes across the membrane.
   – Accounts for 5% of resting metabolic rate of
     many marine and freshwater bony fish
   – Some fish that live in extremely salty lakes
     like Utah’s Great Salt Lake use up to 30% of
     their resting metabolic rate
   – Osmoconformers expend very little energy
• Stenohaline are animals that cannot
  tolerate substantial changes in external
• Euryhaline animals can survive large
  fluctuations in external osmolarity
  – Includes both osmoconformers and certain
  – Species of Salmon; Talapia can adjust to any
    salt concentration between freshwater and
    twice that of salt water
          Marine Adaptations
• Most marine animals are always losing
  water through osmosis
• The sum of their total osmolarity equals
  that of the environment but specific
  solute concentrations differ
  – Even osmoconformers need to regulate
    their internal composition of solutes.
    (marine invertebrates)
• Marine vertebrates and some
  invertebrates are osmoregulators
• Marine bony fish, like cod, are hypoosmotic
  to seawater and constanly lose water and
  gain salt
   – Counteract this by drinking a lot of
     seawater and gills dispose of salt
• Marine sharks and chondrichthyans have
  kidney’s that remove some salt and rectal
  gland removes the rest
   – Maintain high concentration of urea and
     organic solute TMAO to protect from
     damage from urea
   – Actually hyperosmotic to environment and
     urine disposes of small influx of water
            Freshwater Animals
• Constantly gaining water by osmosis and
  lose salts by diffusion (osmolarity of internal
  fluids is much higher than its surroundings)
• Body fluids are lower solute concentrations
  than marine relatives
• Reduced osmotic difference between body
  fluids and the surroundings reduces energy
  needed for osmoregulation
• Maintain water balance by execreting large
  amounts of very dilute urine
• Salt is replenished by food and Cl- is actively
  transported across gills and Na+ follows
     Marine and Freshwater Fish
• Salmon and other euryhaline fish
  migrate between seawater and fresh
• In the ocean, osmoregulation is done
  like marine fish by drinking seawater
  and exereting excess salt from gills
• In fresh water, salmon cease drinking
  and begin to produce large amounts of
  dilute urine and gills take up salt
            Temporary Waters
• Anhydrobiosis is an adaptation that
  aquatic invertebrates have that allow
  them to survive in a dormant state when
  temporary ponds and films of water dry
  – Tardigrades, tiny invertebrates, have 85%
    water mass in hydrated state and 2% water
    in inactive state
  – Must have adaptations to keep cell’s
    membranes in tact--use trehalose, a
    disaccharide, to replace water of their
    membranes when dehydrated
               Land Animals
• Body coverings prevent dehydration
   – Many terrestrial animals, esp. desert
     dwellers are nocturnal because low
     temperature and high humidity
• Animals still lose a lot of water through
  gas exchange, urine, feces, and across
• Balance water budget by drinking
  liquid, eating food, and using metabolic
  water produced during cellular
Water Gain
                             Ingested in

                                                       Ingested in

                                                         Derived from
                        Derived from                     metabolism
                        metabolism              Ingested in liquid
                     feces                     feces
 Water Loss

              Transport Epithelium
• Most animals have one or more kinds of transport
  epithelium, layer of specialized epithelial cells that
  regulate solute movements
   – Essential for osmotic regulation and metabolic
     waste disposal
   – Move specific solute in controlled amounts in
     specific directions
   – Some face outside directly, others line channels
     that connect to outside. This ensures that
     solutes going between animal and environment
     must pass through selectively permeable
   – In most animals, Transport epithelium are
     arranged in tubular networks with extensive
     surface areas.
                   Primary Wastes
Primary waste products of all organisms include:
   • Nitrogen–based products such as urea created by the
   breakdown of proteins into amino acids
   •Water and carbon dioxide created by the breakdown of
Carbon dioxide and some water excretion performed by the
respiratory system. These wastes are toxic to the body if
not removed
Nitrogen and
water are
processed and
released by the
excretory and
urinary system
            Nitrogenous Waste
• Since water is needed to dissolve
  waste before it is removed, waste can
  have large effect on water balance
• When proteins and nucleic acids are
  broken down it results in ammonia
  – Some animals convert it to other less
    toxic compounds which requires ATP
Forms of Nitrogenous Waste include:
Uric Acid
• Ammonia is very soluble but only tolerable at low
  – Aquatic species excrete this because access to a lot
    of water. (Ammonia is toxic, must be excreted in large,
    dilute quantities)
  – Readily passes through membranes and lost by
    diffusion to the surrounding water
  – In invertebrates, it can occur across the whole body
  – In fishes, most ammonia is lost in form of ammonium
    ions across epithelium of gills, kidneys excrete minor
    amounts of nitrogenous wastes
  – Freshwater fish: gill epithelium takes up sodium ions
    from water in exchange for ammonium ions while
    helps maintain a higher sodium concentration in body
    fluids than surrounding water
• Urea is ammonia and carbon dioxide
  – Low toxicity (100,000X less than ammonia)
  – Animals can transport and store Urea safely
  – Requires much less water, more suitable for
    terrestrial animals because less water is lost when a
    given quantity of nitrogen is excreted
  – Allows waste to be excreted in concentrated
    solutions (Good for land animals)
  – Must expend energy to produce it from ammonia
  – Excreted by mammals, adult amphibians, sharks
    and some marine bony fish, and turtles
                Uric Acid
• Insects, land snails, and many reptiles
  excrete uric acid
   – Relatively nontoxic
   – Largely insoluble in water
   – Excreted as semi-solid paste with little
   – Takes even more energy than urea but
     saves water
   – Excreted by insects, land snails, many
     reptiles, land birds
Uric Acid   Ammonia

• Water seems to have most significant on evolution
  of wastes
   – Uric acid and urea show minimal water loss
• Reproduction effected waste too
   – Mammals need soluble wastes so waste can
     diffuse out of embryo
   – Shelled eggs (produced by birds and reptiles)
     need uric acid because it can be stored in the
     egg until the animal hatches. Shelled eggs are
     permeable to gases, not liquids. Soluble
     nitrogenous wastes released by embryo would
     be trapped with in egg and could accumulate to
     dangerous levels.
• Waste of vertebrates depend on habitat
  and evolutionary lineage
  – Terrestrial turtles excrete uric acid while
    aquatic excrete urea and ammonia
• Some species that move between land
  and aquatic environments can change
  their waste products
• Waste also depends on the energy
  – Endotherms eat more food and produce
    more waste than ectotherms
  – Predators that eat more proteins excrete
    more nitrogen
Excretory systems are diverse but go
     through same basic steps
• Body fluid is collected which usually
  involves filtration
  – Hydrostatic pressure forces small solutes (the
    filtrate) into the excretory system
• Selective Reabsorption uses active
  transport to put valuable solutes back into
• Selective Secretion uses active transport
  to add to the filtrate nonessential solutes
  that remain in the body
                  Phylum Porifera
A variety of excretory structures have evolved in
the animal kingdom. Lower classes order
organisms such as protozoa use a contractile
vacuole. Marine animals may have evolved from
a type of protozoan.
•Sponges lack organs and instead have
specialized cells for carrying out bodily functions
•Collar cells lining the inner cavity. The beating
Flagella on Collar Cells create a current which
flows through pores in sponge wall into a central
cavity and through an osculum.
•10 cm tall sponge will go through 100 Liters of
The cnardians such as jellyfish are also examples of
simple organisms that are able to regulate fluids and
wastes without the benefit of any excretory
--They have only the endoderm and ectoderm layers,
making them diplobastic. They lack a mesoderm, and
therefore lack organs.
--They have one opening which serves as both a mouth
an anus
• Molluscs: The mantle cavity, houses
  the gills; the excretory system
  discharge into it. Excretion is carried
  out by a pair of nephridia, that collect
  fluids from the coelom and exchange
  salts and other substances with body
  tissues as the fluid passes along the
  tubules for excretion. The nephridia
  empty into the mantle cavity.
Phylum Platyhelminthes Protonephridia: Flame
                Bulb Systems
 • Freshwater flatworms use this system
   which is a network of dead end tubules
   lacking internal openings
   – Tubules branch throughout the body and
     smallest branches have a flame bulb
   – Bulb has a tuft of cilia that draws water and
     solutes from interstitial fluid and moves the
     urine outward through tubules
   – Dilute urine leaves through nephridiopores
     and counter balances osmotic uptake of
• Has internal openings that collect body fluids
  – Found in annelids like earthworms
  – Each segment of worm has pair of
  – Internal opening are surrounded by ciliated
    funnels (nepthrostome)
  – Fluid enters the nephrostome and passes
    through a coiled collecting tubule which
    includes a bladder
• Have both excretory and osmoregulatory function
  – Produce dilute urine to counter water influx
  – Transport epithelium reabsorbs most solutes
    and returns them to blood
           Malpighian Tubules
• Insects and terrestrial anthropods have
  malphihian tubules that remove nitrogenous
  wastes and also osmoregulate
   – Open into digestive tract and dead ends are
     immersed in hemolymph
   – Transport epithelium secrete solutes (wastes)
     into tubule
   – Waster follows and fluid passes into rectum
   – Most solutes are pumped back into
     hemolymph and water follows again
   – Waste is eliminated as nearly dry matter
• Very effective in conserving water
•   The kidneys are important excretory and water-regulating
    organs that conserve or rid the body of water as
    appropriate in chordates.

• Fishes: As with many aquatic animals, most fish release
  their nitrogenous wastes as ammonia. Some of the wastes
  diffuse through the gills into the surrounding water. Others
  are removed by the kidneys, excretory organs that filter
  wastes from the blood. Kidneys help fishes control the
  amount of ammonia in their bodies. Saltwater fish tend to
  lose water because of osmosis. In saltwater fish, the
  kidneys concentrate wastes and return as much water as
  possible back to the body. The reverse happens in
  freshwater fish, they tend to gain water continuously. The
  kidneys of freshwater fish are specially adapted to pump
  out large amounts of dilute urine. Some fish have specially
  adapted kidneys that change their function, allowing them
  to move from freshwater to saltwater.
• Liquid wastes travel through       • Urogenital System
  ureters into urinary bladder.
• Solid wastes pass from the
  large intestine into the cloaca.
• Liquid and solid waste leave
  through cloaca and the cloacal
• Terrestrial amphibians excrete
  nitrogenous wastes in the form
  of urea - less toxic than
  ammonia and can be
  concentrated to conserve
• Urea produced in liver -
  requires more energy to
  produce than ammonia.              • Kidneys: Filter Blood
• Kidneys lobulated.                        Reptiles
• Renal arteries receive blood from the renal portal
• Nitrogenous wastes in the form of ammonia, urea,
  uric acid or a combination of these.
• Crocodilians, snakes and some lizards do not have
  a urinary bladder. In lizards with a bladder, it is
  connected to the cloaca by a short urethra.
• Urine passes into the cloaca and then into the
  urinary bladder, if present, or into the distal colon
  where water resorption occurs.
• The cloaca typically consists of 3 chambers.
• 1. coprodeum 2.urodeum. 3.The caudal
•   Birds eliminate uric acid with their
•   Bird droppings is uric acid. Not
    very toxic and is not very soluble
    in water.
•   Uric acid conserves water since it
    is produced in concentrated form
    due to its low toxicity.
•   Due to insolubility and nontoxicity,
    can accumulate in eggs without
    damaging the embryos.
•   Synthesis of uric acid requires
    more energy than urea synthesis.
•   There is no urinary bladder in

• Two major excretory
  processes - formation of urine
  and feces.
• Waste eliminated by urination
  and defecation.
• Urine is waste product of
  urinary system while feces
  waste products of the digestive
• Feces contain harmful
• Urine, contains excess water,
  salt, and protein waste. It
  seldom carries any pathogens.
• Variations in nephron structure and function allow
  the kidneys of different vertebrates for
  osmoregulation in various habitats
  Antidiuretic Harmone (ADH)
• ADH is produced in the hypothalamus of
  the brain and is released from the
  posterior pituitary gland.
• Osmoreceptor cells in the hypothalamus
  monitor the osmolarity of blood.
• When osmolarity of blood is high:
  - when it rises above a set point of 300mosm/L,
  more ADH is released into the bloodstream. This
  hormone increases water permeability of the
  distal tubules and collecting ducts, increasing
  water reabsorption from the urine (reduces urine
   -After consuming water in food or drink,
  negative feedback decreases the release of
• When osmolarity of blood is low:
  - very little ADH is released and this decreases
  the permeability of the distal tubules and the
  collecting ducts, so water reabsorption is
  reduced, resulting in increased discharge of
  dilute urine (diuresis).
   - Alcohol inhibits ADH release and can cause
• When osmolarity of blood is high:
  - when it rises above a set point of 300mosm/L,
  more ADH is released into the bloodstream. This
  hormone increases water permeability of the
  distal tubules and collecting ducts, increasing
  water reabsorption from the urine (reduces urine
   -After consuming water in food or drink,
  negative feedback decreases the release of
          system (RAAS)
• The juxtaglomerular apparatus (JGA),
  located near the afferent arteriole leading
  to the glomerulus, responds to a drop in
  blood pressure or volume by releasing
  renin, an enzyme that converts the plasma
  protein angiotensinogen to angiotensin II.
• Angiotensin II functions as a hormone and
  constricts arterioles, stimulates the
  proximal tubules to reabsorb more NaCl
  and water, and stimulates the adrenal
  glandsto release aldosterone.
• This hormone stimulates Na+ and water
  reabsorption in the distal tubules.
• The renin-angiotensin-aldosterone system
  (RAAS) is a homeostatic feedback circuit
  that maintains adequate blood pressure
  and volume.
• A drop in blood pressure and volume
  triggers renin release from the JGA.
• A rise in blood pressure and volume
  reduce the release of renin.

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