Urinary and Excretory System

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Urinary and Excretory System

• Likhitha Musunuru, Sal Ghodbane, and Margaret
  Strair

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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

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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 environment
• Control center processes the information it
  receives from the receptor and directs a response
  by the effector

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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

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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
  babys head pushes against the uterus triggering
  heightening of contractions which causes even
  greater pressure

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Means of Maintaining Homeostasis

• Rid organisms of waste products
• Keep both the fluid and the salt content of the
  organism within normal parameters
• Keep the concentration of other substances in
  body fluids at normal levels

ACHIEVED THROUGH TWO PROCESSES 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
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Review of Osmosis

• All animals face the same problem of
  osmoregulation water uptake and loss must
  balance
• ANIMAL CELLS LACK CELL WALLS AND WILL SWELL AND
  BURST IF THERE IS A CONTINUOUS NET UPTAKE OF
  WATER OR SHRIVEL AND DIE IF THERE IS A
  SUBSTANTIAL NET LOSS OF WATER.
• Osmosis occurs when two solutions separated by a
  membrane differ in osmotic pressure or osmolarity
  

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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 in
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Conformer

• 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

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A Continuum

• Regulating and conforming are two extremes of a
  continuum
• No animal is a perfect regulator or conformer
• Some animals regulate some internal conditions
  and allow others to conform

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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

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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
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Energy

• 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 animals 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
  Utahs Great Salt Lake use up to 30 of their
  resting metabolic rate
• Osmoconformers expend very little energy

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• Stenohaline are animals that cannot tolerate
  substantial changes in external osmolarity
• Euryhaline animals can survive large fluctuations
  in external osmolarity
• Includes both osmoconformers and certain
  osmoregulators
• Species of Salmon Talapia can adjust to any salt
  concentration between freshwater and twice that
  of salt water

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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

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Examples

• 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 kidneys
  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

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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

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Marine and Freshwater Fish

• Salmon and other euryhaline fish migrate between
  seawater and fresh water
• 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

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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 up
• Tardigrades, tiny invertebrates, have 85 water
  mass in hydrated state and 2 water in inactive
  state
• Must have adaptations to keep cells membranes in
  tact--use trehalose, a disaccharide, to replace
  water of their membranes when dehydrated

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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 skin
• Balance water budget by drinking liquid, eating
  food, and using metabolic water produced during
  cellular respiration

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Water Gain
Ingested in food
Ingested in food
Derived from metabolism
Derived from metabolism
Ingested in liquid
feces
feces
Urine
evaporation
Water Loss
urine
evaporation
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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 membrane
• In most animals, Transport epithelium are
  arranged in tubular networks with extensive
  surface areas.

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Primary Wastes

• Primary waste products of all organisms include
• Nitrogenbased products such as urea created by
  the breakdown of proteins into amino acids
• Water and carbon dioxide created by the breakdown
  of carbohydrates

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
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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 Ammonia Urea U
ric Acid
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Ammonia

• Ammonia is very soluble but only tolerable at low
  concentrations
• 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 structure
• 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

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Urea

• 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

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Uric Acid

• Insects, land snails, and many reptiles excrete
  uric acid
• Relatively nontoxic
• Largely insoluble in water
• Excreted as semi-solid paste with little water
• Takes even more energy than urea but saves water
• Excreted by insects, land snails, many reptiles,
  land birds

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Ammonia
Uric Acid
Ammonia
Urea
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Evolution

• 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.

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• 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 budget
• Endotherms eat more food and produce more waste
  than ectotherms
• Predators that eat more proteins excrete more
  nitrogen

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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 system
• Selective Secretion uses active transport to add
  to the filtrate nonessential solutes that remain
  in the body

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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
  water/day

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Cnardians
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 structures. --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
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Invertebrates

• 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.

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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 water

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Metanephridia

• Has internal openings that collect body fluids
• Found in annelids like earthworms
• Each segment of worm has pair of metanephridia
• 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

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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

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CHORDATES

• 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.

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Amphibians

• Liquid wastes travel through ureters into urinary
  bladder.
• Solid wastes pass from the large intestine into
  the cloaca.
• Liquid and solid waste leave through cloaca and
  the cloacal vent.
• Terrestrial amphibians excrete nitrogenous wastes
  in the form of urea - less toxic than ammonia and
  can be concentrated to conserve water.
• Urea produced in liver -requires more energy to
  produce than ammonia.

• Urogenital System
• Kidneys Filter Blood

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Reptiles

• Kidneys lobulated.
• Renal arteries receive blood from the renal
  portal system.
• 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 proctodeum.

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Birds

• Birds eliminate uric acid with their feces.
• 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 birds.

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Mammals

• 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 system.
• Feces contain harmful materials.
• Urine, contains excess water, salt, and protein
  waste. It seldom carries any pathogens.

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• Variations in nephron structure and function
  allow the kidneys of different vertebrates for
  osmoregulation in various habitats

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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.

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continued

• 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
  volume)
• -After consuming water in food or drink,
  negative feedback decreases the release of ADH.

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continued

• 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
  dehydration.

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continued

• 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
  volume)
• -After consuming water in food or drink,
  negative feedback decreases the release of ADH.

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Renin-angiotensin-aldosterone 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.

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continued

• 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.

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continued

• 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.