Osmoregulationand

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• Osmoregulationand
• Excretion

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• Osmoregulation Regulation of solute
  concentrations and water balance by a cell or
  organism.
• Osmoregulation balances the uptake and loss of
  water and solutes.

3

• If cells uptake too much water they will burst
• If cells uptake too little water, or lose too
  much water they will shrivel and die.
• Osmoregulation is impacted by water intake/loss
  and also discharge of metabolic wastes.

4

• Osmosis movement of water across a selectively
  permeable membrane when two solutions separated
  by the membrane differ in osmotic pressure.

Initial flaccid cell
0.4 M sucrose solution
Distilled water
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• Osmolarity(osmotic pressure) Total solute
  concentration expressed as molarity (moles of
  solute per liter of solution).
• Unit of osmolarity milliOsmoles per liter
  (mOsm/L) equivalent to solute concentration of
  10-3M.
• Human blood 300 mOsm/L
• Seawater 1000 mOsm/L

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• Isotonic two solutions on either side of the
  membrane have same osmolarity no net movement of
  water between two sides.
• Hyperosmotic/ hypertonic the solution with
  greater solute concentration (net movement of
  water towards this side)
• Hypoosmotic/ hypotonic the more dilute solution
  (net movement of water away from this side)
• An animal has to have a way of maintaining water
  balance with its environment.

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• Osmoconformer
• Isoosmotic with the surroundings
• Internal osmolarity same as the environment
• No net gain or loss of water
• All marine

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• Osmoregulator
• Maintains its osmolarity independent of the
  environment.
• Because of the regulatory capacity can live in
  freshwater, dry land, also marine habitats
• In hypoosmotic environment they discharge excess
  water
• In hyperosmotic environment they take up and
  retain more water.

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• Based on what you know so far about
  thermoregulation can you make any guesses about
  osmoregulation in these two groups?
• Balancing act between control and cost.

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• Stenohaline Cannot tolerate substantial changes
  in external osmolarity
• Euryhaline Can tolerate large fluctuations in
  osmolarity (organisms in intertidal zones, fishes
  that migrate between sea water and fresh water)
• Osmoregulators and osmoconformers can be found in
  both these groups.

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• Some organisms in a tidal pool

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• Marine invertebrates osmoconformes, need to
  transport some solutes to maintain homeostatis.

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• Marine bony fishes
• lose water by osmosis
• drink large amounts of water
• actively transport out Cl- (chloride cells)
• passively transport out Na
• concentrated urine gets rid of other salts like
  Ca, Na, Mg

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Gain of water and salt ions from food and by
drinking seawater
Osmotic water loss through gills and other
parts of body surface
Excretion of salt ions and small amounts of
water in scanty urine from kidneys
Excretion of salt ions from gills
Osmoregulation in a saltwater fish
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• Marine cartilaginous fishes
• Shark tissue contains a high concentration of
  urea
• To prevent urea from damaging other organic
  molecules in the tissues they have trimethyl
  amine oxide (TMAO)
• Because of high solute concentration in tissue
  water enters the cells (sharks dont drink)
• Produce concentrated urine.

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• Fresh water organisms (opposite problem of
  marine organisms)
• Internal osmolarity is higher than surroundings
  problem of gaining water.
• Fishes dont drink water , large volumes of urine
• Salt intake through food
• Chloride cells in gills actively transport in Cl-
• Na follows

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Osmotic water gain through gills and other
parts of body surface
Uptake of water and some ions in food
Uptake of salt ions by gills
Excretion of large amounts of water in
dilute urine from kidneys
Osmoregulation in a freshwater fish
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• Euryhaline organisms like salmon
• In sea they drink sea water and discharge salt
  through their gills
• In freshwater they stop drinking and produce
  large volumes of dilute urine, gills take up salt

Life Cycle of Atlantic Salmon http//www.nefsc.noa
a.gov/sos/spsyn/af/salmon/images/fig41_2.gif
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• Anhydrobiosis dormant state when habitat dries
  up. 85 to 2 water in water bears. Cell
  membrane adaptations are poorly understood.

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100 µm
100 µm
Dehydrated tardigrade
Hydrated tardigrade
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• Land animals
• Adaptations of body surface (thick cuticle) and
  behavior (nocturnal) help reduce water loss.
• Some desert animals can metabolically generate
  water (kangaroo rats)

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Water balance in a kangaroo rat (2 mL/day)
Water balance in a human (2,500 mL/day)
Ingested in food (750 mL)
Ingested in food (0.2 mL)
Ingested in liquid (1,500 mL)
Water gain
Derived from metabolism (1.8 mL)
Derived from metabolism (250 mL)
Feces (100 mL)
Feces (0.09 mL)
Urine (1,500 mL)
Urine (0.45 mL)
Water loss
Evaporation (900 mL)
Evaporation (1.46 mL)
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• Transport epithelia Animals that live on sea
  water can also eliminate salt through specialized
  epithelial cells that can regulate the salt
  concentration.

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Nasal salt gland
Nostril with salt secretions
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• Nitrogenous wastes
• As a result of metabolism proteins and amino
  acids produce ammonia (NH3).
• Ammonium ion (NH4) is highly toxic
• Animals either get rid of ammonia promptly or
  expend energy and convert it to less toxic forms.

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• Forms of nitrogenous wastes
• ammonia
• urea
• uric acid
• (differ in cost to convert and toxicity)

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• Ammonia
• Most fishes, animals that produce shell-less
  eggs.
• Excrete bulk of ammonia through gills, minor
  amounts through kidneys.
• Very toxic, has to be transported in very dilute
  solutions

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• Urea
• Mammals, adult amphibians, some marine , bony
  fishes, sharks, turtles.
• Advantage Lower toxicity. Can go through
  circulatory system, stored. Does not have to be
  so dilute, so less water loss during excretion.
• Disadvantage High energy cost.
• Animals can switch mode of excretion at different
  stages of their life cycle. Tadpoles (ammonia),
  adult amphibians (urea).

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• Uric acid
• reptiles, birds, land insects, animals that
  produce shelled eggs.
• Advantage less toxic than urea, needs less water
  to be excreted (semisolid paste).
• Disadvantage more expensive to produce than
  urea.
• Humans produce small amounts of uric acid. Gout
  condition caused by inability to eliminate uric
  acid.

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Nucleic acids
Proteins
Nitrogenous bases
Amino acids
NH2 Amino groups
Most aquatic animals, including most bony fishes
Mammals, most amphibians, sharks, some bony fishes
Many reptiles (including birds), insects, land
snails
Ammonia
Urea
Uric acid
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• Amount of nitrogenous waste linked to energy
  budget (higher in endotherms than ectotherms).

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LE 44-9
Capillary
Filtration
Excretory tubule
Filtrate

• Steps in urine formation
• Filtration
• Reabsorption
• Secretion

Reabsorption
Secretion
Urine
Excretion
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• Filtration
• Cells, large molecules (proteins) stay in the
  body fluid
• Small molecules, (salts, sugars, amino acids,
  nitrogenous wastes) and water pass through and
  form filtrate

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• Reabsorption
• Selective process. Recovery of useful molecules
• Active transport reabsorption of certain salts,
  vitamins, hormones, amino acids
• Wastes, nonessential molecules are left behind

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• Secretion
• Selective pumping of various solutes to adjust
  osmotic movement of water into and out of the
  filtrate
• Final step removal of this filtrate from the
  body release of urine

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• Diverse excretory systems
• Excretory system plays a very important role in
  water balance and homeostasis.
• Systems show a lot of variation in different
  groups
• Basic structure network of tubules that provide
  a large surface area

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Nucleus of cap cell
Protonephridia - excrete low concentration of
solute flatworms, some rotifers, some annelids
and molluscs
Cilia
Interstitial fluid filters through membrane
where cap cell and tubule cell interdigitate (inte
rlock)
Tubule cell
Flame bulb
Protonephridia (tubules)
Tubule
Nephridiopore in body wall
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• Metanephridia - found in most annelids (e.g.
  earthworms) excretory organs open internally to
  the coelom

Coelom
Capillary network
Bladder
Collecting tubule
Nephridio- pore
Nephrostome
Metanephridium
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• Malpighian tubules
• extend from hemolymph to digestive tract
• cells secrete nitrogenous wastes and other
  solutes into hemolymph,
• these molecules and water move into malpighian
  tubules,
• excess water is reabsorbed in the rectum
• other essential solutes are reabsorbed
• lets the animal conserve water
• found in insects, capability to conserve water
  helps in the success of this group

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Digestive tract
Rectum
Hindgut
Intestine
Midgut (stomach)
Malpighian tubules
Salt, water, and nitrogenous wastes
Anus
Feces and urine
Malpighian tubule
Rectum
Reabsorption of H2O, ions, and valuable organic
molecules
HEMOLYMPH
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• Kidneys vertebrates and some other chordates,
  same basic plan as other systems but highly
  organized and complex, closely associated with a
  network of capillaries.

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• Nephron functional unit of a kidney

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• Structure of mammalian excretory system

Posterior vena cava
Renal artery and vein
Kidney
Renal medulla
Aorta
Renal cortex
Ureter
Renal pelvis
Urinary bladder
Urethra
Ureter
Excretory organs and major associated blood
vessels
Section of kidney from a rat
Kidney structure
Juxta- medullary nephron
Cortical nephron
Afferent arteriole from renal artery
Glomerulus
Bowmans capsule
Proximal tubule
Peritubular capillaries
Renal cortex
Collecting duct
SEM
20 µm
Efferent arteriole from glomerulus
Renal medulla
Distal tubule
To renal pelvis
Collecting duct
Branch of renal vein
Descending limb
Loop of Henle
Nephron
Ascending limb
Vasa recta
Filtrate and blood flow
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Kidney
Renal medulla
Renal cortex
Renal pelvis
Ureter
Section of kidney from a rat
Kidney structure
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Juxta- medullary nephron
Cortical nephron
Renal cortex
Collecting duct
Renal medulla
To renal pelvis
Nephron
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Afferent arteriole from renal artery
Glomerulus
Bowmans capsule
Proximal tubule
Peritubular capillaries
SEM
20 µm
Efferent arteriole from glomerulus
Distal tubule
Collecting duct
Branch of renal vein
Descending limb
Loop of Henle
Ascending limb
Vasa recta
Filtrate and blood flow
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• Detailed look at processing of blood in nephron
• Filtration
• Afferent arteriole has a bigger diameter than
  efferent arteriole, thus pressure builds in the
  glomerulus
• During filtration, blood in glomerulus is forced
  into Bowmans capsule (cup shaped swelling at the
  blind end of the tubule)
• Filtration is nonselective, only based on size,
  caused by the high blood pressure in the
  capillaries in the Bowmans capsule.

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• Microscopic view of Bowmans capsule

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• From filtrate to urine
• Filtrate contains water, salts (like NaCl),
  bicarbonate ions, hydrogen ions, urea, glucose,
  amino acids, drugs

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Proximal tubule
Distal tubule
NaCl
Nutrients
H2O
HCO3
K
H2O
HCO3
NaCl
H
NH3
H
K
CORTEX
Descending limb of loop of Henle
Thick segment of ascending limb
Filtrate
H2O Salts (NaCl and others) HCO3 H Urea Glucose
amino acids Some drugs
NaCl
H2O
OUTER MEDULLA
NaCl
Thin segment of ascending limb
Collecting duct
Key
Urea
NaCl
Active transport Passive transport
H2O
INNER MEDULLA
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• Proximal tubule very critical recapture, to
  reabsorb nutrients and to maintain homeostasis in
  this case by maintaining pH and water balance
• Na, is reabsorbed by active transport, Cl- ions
  follow
• Nutrients are absorbed actively
• H is actively secreted into the tubule and NH3
  is transported passively to regulate the pH of
  the urine.
• HCO3- is passively reabsorbed
• Urine becomes more concentrated

Proximal tubule
NaCl
Nutrients
HCO3
K
H2O
H
NH3
CORTEX
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• Descending loop of Henle
• Cells lining the tubule here have special water
  transport proteins called aquaporins.
• Cells lining the DLH are hyper osmotic, water
  moves out by osmosis
• Reabsorption of other solutes not significant

Proximal tubule
NaCl
Nutrients
HCO3
K
H2O
H
NH3
CORTEX
Descending limb of loop of Henle
H2O
OUTER MEDULLA
INNER MEDULLA
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• Ascending loop of Henle
• Transport epithelium has ions channels (actively
  transports out NaCl)
• Transport epithelium does not have water channels
  
• Filtrate become more dilute as it travels up ALH.

Proximal tubule
NaCl
Nutrients
HCO3
K
H2O
H
NH3
CORTEX
Descending limb of loop of Henle
Thick segment of ascending limb
NaCl
H2O
OUTER MEDULLA
Thin segment of ascending limb
NaCl
INNER MEDULLA
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• Distal tubule
• Regulates K, H, NaCl and HCO3- and maintains
  ion concentration in the body
• Collecting duct
• Urea is absorbed in the deeper parts of the
  collecting duct.
• Water absorption is controlled by hormones

Proximal tubule
Distal tubule
NaCl
Nutrients
H2O
HCO3
K
H2O
HCO3
NaCl
H
NH3
H
K
CORTEX
Descending limb of loop of Henle
Thick segment of ascending limb
NaCl
H2O
OUTER MEDULLA
NaCl
Thin segment of ascending limb
Collecting duct
Urea
NaCl
H2O
INNER MEDULLA
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• 1600L of blood flows through the human kidney
  (300 times the total blood volume)
• 180L of initial filtrate is produced in the
  kidney
• 1.5L of urine is voided

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• Kidneys role in water conservation
• Human kidney can produce urine that is 4 to 5
  times more concentrated than blood.
• Some desert animals can produce urine that is 25
  times more concentrated than blood
• Production of hyperosmotic urine is very energy
  consuming
• Two solutes that play a key role in control of
  urine osmolarity NaCl and urea

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• Two solute model
• Filtrate from Bowmans capsule has same
  osmolarity as blood.
• At the proximal tubule water and salts are
  reabsorbed, so volume decreases but osmolarity
  stays the same.
• While going through DLH osmolarity increases
  because water is absorbed epithelium is permeable
  to water not salts
• Highest osmolarity occurs at the elbow of Loop of
  Henle

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Osmolarity of interstitial fluid (mosm/L)
300
300
100
300
100
300
300
H2O
CORTEX
Active transport
400
200
400
400
H2O
Passive transport
H2O
OUTER MEDULLA
H2O
600
400
600
600
H2O
H2O
700
900
900
H2O
INNER MEDULLA
1200
1200
1200
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• In the Ascending limb (permeable to salts and not
  water) osmolarity decreases
• Loop of Henle creates concentration gradients, by
  expending energy countercurrent multiplier
  system.

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Osmolarity of interstitial fluid (mosm/L)
300
300
100
300
100
300
300
NaCl
H2O
CORTEX
Active transport
400
200
400
400
H2O
NaCl
Passive transport
NaCl
H2O
OUTER MEDULLA
H2O
NaCl
600
400
600
600
H2O
NaCl
H2O
NaCl
700
900
900
H2O
NaCl
INNER MEDULLA
1200
1200
1200
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• Ascending and descending vessels of vasa recta
  blood flows in the opposite direction as the
  kidneys osmolarity gradient
• As blood flows down towards the inner medulla,
  blood looses water and gains NaCl
• As blood flows away from the medulla towards the
  cortex, water is gained and NaCl is lost

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• Urea enters the loop of Henle by diffusion but
  some leaks out of the collecting duct. This
  maintains the high osmolarity of the interstitial
  fluid, draws water out of the filtrate in the
  collecting duct and keeps urine hyperosmotic.
• Urine is isotonic to the interstitial fluid of
  inner medulla but hyperosmotic to blood

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Osmolarity of interstitial fluid (mosm/L)
300
300
100
300
100
300
300
NaCl
H2O
H2O
CORTEX
Active transport
400
200
400
400
H2O
NaCl
H2O
Passive transport
NaCl
H2O
H2O
OUTER MEDULLA
H2O
NaCl
H2O
600
400
600
600
H2O
NaCl
H2O
Urea
H2O
NaCl
H2O
700
900
900
Urea
H2O
H2O
NaCl
INNER MEDULLA
Urea
1200
1200
1200
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• Like counter current exchange but this process
  costs a lot of energy expenditure.
• This counter current-like system helps maintain
  the steep gradient, it is not lost due because
  the active transport maintains it
• For its size energy consumes a lot of ATP

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• Adaptations of vertebrate kidney to a variety of
  environments
• Mammalian kidney very well adapted to terrestrial
  life juxtamedullary nephron is very well
  adapted to produce hyperosmotic urine.

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• Animals in drier environments need to produce
  more hyperosmotic urine, have longer Loop of
  Henle and deeper medulla
• Animals in watery environments have shorter Loop
  of Henle and less ability to concenmtarte urine

Bannertail kangaroo rat (Dipodomys spectabilis)
Beaver (Castor canadensis)
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• Birds
• Kidneys do not have nephrons that extend into the
  medulla
• Chief water conservation adaptation is production
  of uric acid
• Reptiles
• Produces uric acid
• Have cortical nephrons which produce urine that
  is isotonic or even hypertonic to blood but water
  is reabsorbed in cloaca and urine discharged from
  the body is highly concentrated

Roadrunner (Geococcyx californianus)
Desert iguana (Dipsosaurus dorsalis)
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• Freshwater fishes
• Large volume of urine, salts are reabsorbed in
  the distal tubules
• Frogs
• When on land they conserve water by reabsorption
  across the epithelium of the urinary bladder

Rainbow trout (Oncorrhynchus mykiss)
Frog (Rana temporaria)
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• Marine bony fishes
• Problem gain salts from environment and tend to
  lose water
• Lack distal tubule, smaller glomerulous, can
  adjust amount of urine

Northern bluefin tuna (Thunnus thynnus)
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• Kidney function, water balance, blood pressure
  hormonal control
• ADH control RAAS system

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• ADH control
• Osmoregulatory function of kidney is controlled
  by nerves and hormones
• Antidiuretic hormone (ADH)/vasopressin key role
  in osmoregulation
• ADH is produced by hypothalamus and is stored in
  the posterior pituitary
• Hypothalamus monitors blood osmolarity using
  osmoreceptor cells

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• Blood osmolarity rises above 300mOsm/L (eating
  salty food, sweating)
• ADH is released into the bloodstream
• Changes epithelium of distal tubule and
  collecting duct and makes them more permeable to
  water, increases reabsorption of water
• Decreases blood osmolarity and increases urine
  osmolarity by decreasing urine volume
• Blood osmolarity decreases below 300mOsm/L
  (drinking large volumes of fluids)
• ADH secretion goes down
• Permeability of distal tubule and collecting duct
  goes down, less water is reabsorbed
• Volume of urine is high, osmolarity of blood goes
  up

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Osmoreceptors in hypothalamus
Thirst
Hypothalamus
Drinking reduces blood osmolarity to set point

• Osmolarity and ADH are linked by negative
  feedback loop

ADH
Increased permeability
Pituitary gland
Distal tubule
H2O reab- sorption helps prevent
further osmolarity increase
STIMULUS The release of ADH is triggered when
osmo- receptor cells in the hypothalamus detect
an increase in the osmolarity of the blood
Collecting duct
Homeostasis Blood osmolarity
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• Genetic disorders that affect ADH production or
  ADH receptors can affect osmoregulatory function
  of kidney, cause severe dehydration by producing
  very dilute urine diabetes insipidus
• Alcohol inhibits ADH release, can cause excessive
  water loss, some dehydration and symptoms of
  hangover

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Homeostasis Blood pressure, volume

• RAAS (Renin-angiotensin-aldosterone) system
• When blood volume is low, blood pressure drops
• Juxta glomerular apparatus (JGA) located near the
  afferent arteriole releases rennin
• Renin converts angiotensinogen to angiotensin I
• Angiotensin converting enzyme (ACE) converts
  angiotensin I to angiotensin II
• Angiotensin II raises blood pressure by
  constricting arterioles
• Angiotensin II also stimulates secretion of
  aldosterone by adrenal glands
• Causes more reabsorption of Na and water and
  increases blood volume and pressure
• High blood pressure drugs block ACE

Increased Na and H2O reab- sorption in distal
tubules
STIMULUS The juxtaglomerular apparatus (JGA)
responds to low blood volume or blood pressure
(such as due to dehydration or loss of blood)
Aldosterone
Arteriole constriction
Adrenal gland
Angiotensin II
Distal tubule
ACE
Angiotensin I
JGA
Renin production
Renin
Angiotensinogen
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