Osmoregulation and Excretion

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Osmoregulation and Excretion

• A.P. Biology
• Ch. 44
• Rick L. Knowles
• Liberty Senior High School

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Osmoregulation

• Maintaining a balance of both water and ions
  across a membrane/organism. Solute and water
  homeostasis.
• Osmolarity moles of total solute per liter of
  water usually in milliosmoles/L.
• Mechanism of homeostasis varies with the
  environment in which theyve adapted (freshwater,
  saltwater, terrestrial).

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Some Comparison
Freshwater 0.5 -15
0
300 Human Plasma
1,000 Seawater
5,000 Dead Sea
Distilled,deionized Water
Milliosmoles/L (mosm/L)
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• Most animals are said to be stenohaline
• And cannot tolerate substantial changes in
  external osmolarity both osmoconformers and
  osmoregulators.
• Euryhaline animals
• Can survive large fluctuations in external
  osmolarity.

Tilapia, freshwater up to 2,000 mosm/L
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Osmoregulation and Nitrogenous Wastes

• Other waste solutes must be removed from cells
  and organisms.
• A waste product of metabolizing amino acids and
  nucleic acids (deamination)- ammonia.

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• Concept 44.2 An animals nitrogenous wastes
  reflect its phylogeny and habitat.
• The type and quantity of an animals waste
  products
• May have a large impact on its water balance.

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Ammonia

• Direct by-product of protein and nucleic acids
  (deamination).
• Very toxic to cells.
• Highly soluble in water.
• Molecule of choice for freshwater organisms
  eliminated easily through kidneys, gill
  epithelia, etc.
• Downside requires a lot of water.

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Urea

• Saltwater and terrestrial mammals convert ammonia
  into urea.
• Less toxic accumulate more in tissue.
• Less soluble in water than ammonia.
• Allows conservation of water.

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Uric Acid

• Birds and reptiles accumulate waste in an egg.
• Convert ammonia into uric acid.
• Insoluble in water crystallizes.
• Semisolid paste-guano.
• Requires less water to eliminate.

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• Among the most important wastes
• Are the nitrogenous breakdown products of
  proteins and nucleic acids

Figure 44.8
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Osmoconformers

• Most marine protists and invertebrates.
• Are isoosmotic with marine environment.
• Open channels and carriers for most ion transport
  (Not all ions are in equilibrium).
• Ex. Invertebrates like sea anemones, jellyfish,
  and only vertebrate, Class Agnatha- hagfish.

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Class Agnatha- Hagfish
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Show me a real hagfish!

• Video Discovery- Blue Planet Ocean World

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Osmoregulators

• Maintain constant osmotic concentration in body
  fluids and cytoplasm despite external variations.
• Continuous regulation since environment and
  intake (diet) changes.
• Evolved special mechanisms for different
  environments.
• Ex. Most Vertebrates

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The Problems

• Freshwater Vertebrates- are hyperosmotic, water
  enters body, tend to lose ions.
• Marine Vertebrates- are hypoosmotic, water leaves
  body, tend to gain ions.
• Terrestrial Vertebrates- are hypoosmotic, water
  leaves body through respiration, perspiration,
  skin.

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Freshwater Protists

• Problem hyperosmotic impossible to become
  isoosmotic with dilute fresh water tend to gain
  water lose ions no excretory organ.
• Solution Contractile Vacuoles active
  transport of water out of cell less permeable to
  ions
• Downside Active transport requires energy.

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Freshwater Invertebrates

• Water and wastes are passed into a collecting
  vessel or primitive excretory organ.
• Membrane retains proteins and sugars and allows
  water and dissolved wastes to leave-selectively
  permeable.
• Ex. Freshwater jellyfish, etc,

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• Concept 44.3 Diverse excretory systems are
  variations on a tubular theme.
• Excretory systems
• Regulate solute movement between internal fluids
  and the external environment.

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Excretory Processes

• Most excretory systems
• Produce urine by refining a filtrate derived from
  body fluids

Figure 44.9
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Protonephridia Flame-Bulb Systems

• A protonephridium
• Is a network of dead-end tubules lacking internal
  openings.

Figure 44.10
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• The tubules branch throughout the body
• And the smallest branches are capped by a
  cellular unit called a flame bulb.
• These tubules excrete a dilute fluid
• And function in osmoregulation

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Metanephridia

• Each segment of an earthworm
• Has a pair of open-ended metanephridia

Figure 44.11
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• Metanephridia consist of tubules
• That collect coelomic fluid and produce dilute
  urine for excretion.

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Terrestrial Insects

• Problem Must minimize water loss.
• Solution Use chitin as an exoskeleton.

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Malpighian Tubules

• In insects and other terrestrial arthropods,
  malpighian tubules
• Remove nitrogenous wastes from hemolymph and
  function in osmoregulation

Figure 44.12
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Malpighian Tubules
K
Hemolymph
Water and K
K
Water and waste
K
Na/K-ATPase
Conc. Waste
Hindgut
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Malpighian Tubules

• Use Malpighian tubules- blind end tubules that
  extend into hemocoel (body cavity).
• Cells ? waste and salts into hemolymph?lumen of
  tubule by diffusion and active transport.
• K are actively transported into lumen set up a
  gradient.
• Water and other ions leave the hemolymph and
  follow into the lumen by passive diffusion.
• Empty into hindgut water reabsorbed urine is
  concentrated.
• Na/K-ATPase moves ions from lumen of hindgut
  into hemolymph.

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Insects versus other Vertebrates

• Insects use a gradient to pull water through a
  membrane open circulatory system low blood
  pressure.
• Vertebrates- push water through a membrane
  closed circulatory system higher blood pressure.

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More Complex Organisms Need Another Solution

• Introducing the Vertebrate Kidney!

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Nephron (Tubule)
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Gill Epithelia is Permeable
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Hypotonic Env.
Hypertonic Cells
Water
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Freshwater Bony Fishes

• Problems Water enters cells from environment,
  solutes leave cells.
• Solutions Drink very little water excrete
  large amounts of dilute (hypoosmotic) urine with
  large kidneys reabsorb ions in kidney tubules
  (active transport) back into blood use chloride
  cells in gill epithelium (active transport).

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• Freshwater animals maintain water balance
• By excreting large amounts of dilute urine.
• Salts lost by diffusion
• Are replaced by foods and uptake across the gills.

Figure 44.3b
(b) Osmoregulation in a freshwater fish
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Hypotonic Cells
Water
Hypertonic Env.
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Saltwater Bony Fishes

• Problem Tend to lose water, gain ions, mostly
  at gills.
• Solutions Drink large amount of water kidney
  retains water and excretes ions (isoosmotic
  urine) use chloride cells in gills to actively
  transport some ions across gill epithelium.

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• Marine bony fishes are hypoosmotic to sea water
• Lose water by osmosis and gain salt by both
  diffusion and from food they eat.
• These fishes balance water loss
• By drinking seawater.

Figure 44.3a
(a) Osmoregulation in a saltwater fish
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Cartilaginous Fishes

• Problem Same as marine bony fishes.
• Solution Reabsorb urea from nephron tubule back
  into the blood 100X blood urea than mammals
  (special protective solute,TMAO to protect
  proteins)?blood is slightly hyperosmotic? kidneys
  and gills do not have to remove ions do not have
  to drink large volume of water.

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Cartilaginous Fishes

• Problem Still must remove excess Na and Cl-
  that diffuse across gills, diet, etc.
• Solution Rectal Gland- uses Na/K-ATPase
  pumps to actively transport Na and Cl- out of
  blood by setting up a gradient.

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How the Rectal Gland Works
Extracellular Fluid
Na
K
Na
Cl-
Na/K-ATPase
Na
Cotransporter
Cl-
Na
Cl-
Chloride Channel
Na
Cl-
To Rectum
Lumen of Rectal Gland
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How could a marine shark enter freshwater?

• By controlling the amount of solutes!
• Video National Geographic Presents Attacks of
  the Mystery Shark

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Rectal Gland

• Very common mechanism for removing salt in marine
  animals.
• Problem Marine birds and reptiles have
  freshwater kidneys designed to reabsorb salt from
  urine into blood.
• Use similar salt glands in nostrils to excrete
  salt.

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• An example of transport epithelia is found in the
  salt glands of marine birds.
• Remove excess sodium chloride from the blood.

Figure 44.7a, b
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Show me some marine reptiles! Salt glands in
action!

• Video Corwin Experience- Galapagos

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Animals That Live in Temporary Waters

• Some aquatic invertebrates living in temporary
  ponds
• Can lose almost all their body water and survive
  in a dormant state
• This adaptation is called anhydrobiosis.

Figure 44.4a, b
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• The nephron, the functional unit of the
  vertebrate kidney
• Consists of a single long tubule and a ball of
  capillaries called the glomerulus

Figure 44.13c, d
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Vertebrate Kidneys

• Four Functions
• 1. Filtration
• 2. Reabsorption
• 3. Secretion
• 4. Excretion

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1. Filtration

• Glomerulus- tightly-woven ball of capillaries
  embedded in a cup-shaped tubule- Bowmans
  capsule.
• Slits/pores in capillaries and capsule allow
  liquid/solutes through but prevent cells and
  large proteins from entering the nephron.
• Produces isoosmotic filtrate with blood

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Filtration of the Blood

• Filtration occurs as blood pressure
• Forces fluid from the blood in the glomerulus
  into the lumen of Bowmans capsule.

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Pathway of the Filtrate

• From Bowmans capsule, the filtrate passes
  through three regions of the nephron
• The proximal tubule, the loop of Henle, and the
  distal tubule
• Fluid from several nephrons
• Flows into a collecting duct

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Blood Vessels Associated with the Nephrons

• Each nephron is supplied with blood by an
  afferent arteriole
• A branch of the renal artery that subdivides into
  the capillaries
• The capillaries converge as they leave the
  glomerulus
• Forming an efferent arteriole.
• The vessels subdivide again
• Forming the peritubular capillaries, which
  surround the proximal and distal tubules.

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From Blood Filtrate to Urine A Closer Look

• Filtrate becomes urine
• As it flows through the mammalian nephron and
  collecting duct.

Figure 44.14
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Transport Epithelium
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2. Reabsorption

• Must return most of the water and solutes to the
  blood. (2000 l of blood? 180 l water? 1-2 l urine
  daily).
• Reabsorb glucose, amino acids, divalent cations
  in proximal tubule by active transport carriers.
  
• If not reabsorbed, lost in the urine.
• Ex. Diabetes mellitus

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3. Secretion

• Foreign molecules and wastes (ammonia, urea) are
  secreted into lower portions of tubule.
• Opposite direction as reabsorption
  (Capillary?Tubule).
• Ex. Antibiotics and other drugs, bacterial
  debris

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• Secretion and reabsorption in the proximal
  tubule
• Substantially alter the volume and composition of
  filtrate
• Reabsorption of water continues
• As the filtrate moves into the descending limb of
  the loop of Henle

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4. Excretion

• Urine is a solution of
• Harmful drugs, hormones, nitrogenous wastes, and
  excess K, H, water.
• Homeostasis of
• pH, electrolytes, blood volume and pressure.

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• As filtrate travels through the ascending limb of
  the loop of Henle
• Salt diffuses out of the permeable tubule into
  the interstitial fluid.
• The distal tubule
• Plays a key role in regulating the K and NaCl
  concentration of body fluids.
• The collecting duct
• Carries the filtrate through the medulla to the
  renal pelvis and reabsorbs NaCl.

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• Concept 44.5 The mammalian kidneys ability to
  conserve water is a key terrestrial adaptation.
• The mammalian kidney
• Can produce urine much more concentrated than
  body fluids, thus conserving water.

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Solute Gradients and Water Conservation

• In a mammalian kidney, the cooperative action and
  precise arrangement of the loops of Henle and the
  collecting ducts
• Are largely responsible for the osmotic gradient
  that concentrates the urine.

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• Two solutes, NaCl and urea, contribute to the
  osmolarity of the interstitial fluid.
• - Causes the reabsorption of water in the kidney
  and concentrates the urine.

Figure 44.15
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• The countercurrent multiplier system involving
  the loop of Henle
• Maintains a high salt concentration in the
  interior of the kidney, which enables the kidney
  to form concentrated urine.

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• The collecting duct, permeable to water but not
  salt
• Conducts the filtrate through the kidneys
  osmolarity gradient, and more water exits the
  filtrate by osmosis.

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• Urea diffuses out of the collecting duct
• As it traverses the inner medulla
• Urea and NaCl
• Form the osmotic gradient that enables the kidney
  to produce urine that is hyperosmotic to the
  blood.

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• Antidiuretic Hormone (ADH)
• Increases water reabsorption in the distal
  tubules and collecting ducts of the kidney

(a) Antidiuretic hormone (ADH) enhances fluid
retention by makingthe kidneys reclaim more
water.
Figure 44.16a
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• The Renin-Angiotensin-Aldosterone System (RAAS)
• Is part of a complex feedback circuit that
  functions in homeostasis

(b) The renin-angiotensin-aldosterone system
(RAAS) leads to an increasein blood volume and
pressure.
Figure 44.16b
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• The South American vampire bat, which feeds on
  blood
• Has a unique excretory system in which its
  kidneys offload much of the water absorbed from a
  meal by excreting large amounts of dilute urine.

Figure 44.17
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• Concept 44.6 Diverse adaptations of the
  vertebrate kidney have evolved in different
  environments.
• The form and function of nephrons in various
  vertebrate classes
• Are related primarily to the requirements for
  osmoregulation in the animals habitat.

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Terrestrial Animals

• Land animals manage their water budgets
• By drinking and eating moist foods and by using
  metabolic water.

Figure 44.5
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• Desert animals
• Get major water savings from simple anatomical
  features

Figure 44.6
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• Exploring environmental adaptations of the
  vertebrate kidney

Figure 44.18