Download Osmoregulation File

Reading List
• 
Guyton A C and Hall J E (1996) Textbook
of medical physiology, Prism Books Pvt.
Ltd. India
• 
Ganong W F (1983) Review of medical
physiology. Lange Medical Publications,
California
• 
Schmidt-Nielsen K (1983) Animal
physiology: adaptaion and environment.
Cambridge University Press, London
1
2
Osmalarity & Osmotic
Balance
Osmoregulation &
Excretion
l 
Water in a multicellular body distributed
between
•  Intracellular compartment
•  Extracellular compartment
Dr. Dinithi Peiris
Dept. of Zoology
l 
Most vertebrates maintain homeostasis for
•  Total solute concentration of their extracellular
fluids
•  Concentration of specific inorganic ions
3
4
1
Osmalarity & Osmotic
Balance
l 
Osmalarity & Osmotic
Balance
Important ions
l 
•  Sodium (Na+) is the major cation in extracellular
Osmoconformers
•  Organisms that are in osmotic equilibrium with
fluids
•  Chloride (Cl–) is the major anion
their environment
•  Among the vertebrates, only the primitive
hagfish are strict osmoconformers
•  Sharks and relatives (cartilaginous fish) are also
isotonic
l 
5
6
Osmalarity & Osmotic
Balance
Osmalarity & Osmotic
Balance
l 
All other vertebrates are osmoregulators
•  Maintain a relatively constant blood osmolarity
Freshwater vertebrates
•  Hypertonic to their environment
•  Have adapted to prevent water from entering their
bodies, and to actively transport ions back into their
bodies
despite different concentrations in their
environment
l 
7
Marine vertebrates
•  Hypotonic to their environment
•  Have adapted to retain water by drinking seawater
• 
and eliminating the excess ions through kidneys & gills
8
2
Osmoregulation
(a) Osmoregulation in a marine fish
Gain of water
and salt ions
from food
Excretion
of salt ions
from gills
Gain of water
and salt ions
from 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
Osmoregulation
(b) Osmoregulation in a freshwater fish
Gain of water
and some ions
in food
Key
Water
Salt
Uptake of
salt ions
by gills
Osmotic water
gain through
gills and other
parts of body
surface
Excretion of salt ions and
large amounts of water in
dilute urine from kidneys
Animals That Live in Temporary
Waters
•  Some aquatic invertebrates in temporary ponds
lose almost all their body water and survive in a
dormant state
•  This adaptation is called anhydrobiosis
9
10
Osmalarity & Osmotic
Balance
Osmalarity & Osmotic
Balance
l 
Terrestrial vertebrates
l 
Adaptations to reduce water loss are key to
survival on land
•  Higher concentration of water than surrounding
l 
Desert animals get major water savings from
simple anatomical features and behaviors such as
a nocturnal life style
•  Tend to lose water by evaporation from skin and
l 
l 
Land animals maintain water balance by eating
moist food and producing water metabolically
through cellular respiration
11
Terrestrial Animals
air
lungs
•  Body coverings of most terrestrial animals help
prevent dehydration
•  Urinary / osmoregulatory systems have evolved
in these vertebrates that help them retain water
12
3
Osmoregulation &
Energy
Osmoregulation &
Energy
•  Osmoregulators must expend energy to
maintain osmotic gradients
•  The amount of energy differs based on
–  How different the animal s osmolarity is from
its surroundings
–  How easily water and solutes move across
the animal s surface
–  The work required to pump solutes across the
membrane
•  Animals regulate the solute content of body fluid
that bathes their cells
•  Transport epithelia are epithelial cells that are
specialized for moving solutes in specific
directions
•  They are typically arranged in complex tubular
networks
•  An example is in nasal glands of marine birds,
which remove excess sodium chloride from the
blood
13
14
Salt Gland
Salt Gland
Secretory cell
Artery of transport Lumen of
Vein
epithelium
secretory
tubule
Nasal salt
gland
Ducts
Nasal gland
Salt
ions
Secretory tubule
Nostril with salt
secretions
(a) Location of nasal glands
in a marine bird
Transport
epithelium
(b)Secretory
tubules
Blood flow Salt secretion
Salt movement
Blood flow
Central duct
15
16
4
Vein
Secretory cell Lumen of
of transport
secretory
epithelium
tubule
Artery
Nasal gland
Capillary
Secretory tubule
Transport
epithelium
Salt
ions
Salt Gland
Salt Gland
Key
Salt movement
Blood flow
(b) Secretory tubules
Blood flow Salt secretion
Central duct
(c) Countercurrent exchange
17
18
Nitrogenous waste
l 
l 
Vertebrate Kidney
In many animals, removal of water or salts is
coupled with removal of metabolic wastes
through the excretory system
l 
Mammals and birds are the only vertebrates that can
produce urine that is hypertonic to body fluids
l 
Accomplished by the loop of Henle
A variety of mechanisms have evolved to
accomplish this
l 
Birds have relatively few or no nephrons with long
loops, and so cannot produce urine as concentrated
as that of mammals
•  Single-celled protists and sponges use contractile
vacuoles
•  Other multicellular animals have a system of
excretory tubules to expel fluid and wastes
19
20
5
Figure 44.8
An animal s nitrogenous wastes
reflect its phylogeny and habitat
Proteins
Nucleic acids
Amino
acids
Nitrogenous
bases
—NH2
Amino groups
•  The type and quantity of an animal s waste
products may greatly affect its water balance
•  Among the most significant wastes are
nitrogenous breakdown products of proteins
and nucleic acids
Most aquatic
animals, including
most bony fishes
Mammals, most
amphibians, sharks,
some bony fishes
Many reptiles
(including birds),
insects, land snails
•  Some animals convert toxic ammonia (NH3)
to less toxic compounds prior to excretion
Ammonia
21
Figure 44.8a
Urea
Uric acid
Figure 44.8a
Nitrogenous Waste
•  Animals excrete nitrogenous wastes in different
forms: ammonia, urea, or uric acid
•  These differ in toxicity and the energy costs of
producing them
Ammonia
•  Animals that excrete nitrogenous wastes as
ammonia need access to lots of water
•  They release ammonia across the whole body
surface or through gills
6
Figure 44.8a
Figure 44.8a
Urea
Uric Acid
•  Insects, land snails, and many reptiles, including
birds, mainly excrete uric acid
•  The liver of mammals and most adult
amphibians converts ammonia to the less toxic
urea
•  Uric acid is relatively nontoxic and does not
dissolve readily in water
•  The circulatory system carries urea to the
kidneys, where it is excreted
•  It can be secreted as a paste with little water
loss
•  Conversion of ammonia to urea is energetically
expensive; excretion of urea requires less
water than ammonia
•  Uric acid is more energetically expensive to
produce than urea
Nitrogenous Waste
l 
Nitrogenous Waste
NH3 is formed form proteins by 2 main methods
1. Oxidative deamination
AA + ½ O2
Keto Acid + NH3
AA Oxidase
2. AA
Imino Acid + H2O
AA dehyrdrogenase
Keto Acid + NH3
27
3.  Glutamine
Glutamine + H2O
Glutamic Acid+ NH3
Glutaminase
l  Happens specially in the liver cells
l  1st and 2nd methods take place at every cell of
the body
28
7
Nitrogenous Waste
l 
l 
Nitrogenous Waste
When amino acids and nucleic acids are
catabolized, they produce nitrogenous wastes
that must be eliminated from the body
l 
Mammals also produce uric acid, but from
degradation of purines, not amino acids
l 
Most have an enzyme called uricase, which
convert uric acid into a more soluble derivative
called allantoin
l 
Humans lack this enzyme
l 
Excessive accumulation of uric acid in joints
causes gout
First step is deamination
•  Removal of the amino (―NH2) group
• Toxic to cells, and thus it is only safe in dilute
concentrations
29
Other Excretory Products
l 
Guanic acid – Spiders
l 
Tri methyl amino acid – sharks
l 
Petrines – Pigments that are deposited on
wings of butterfly
30
Urea Cycle
31
32
8
Nitrogenous Waste
Nitrogenous Waste
•  Most excretory systems produce urine by
refining a filtrate derived from body fluids
Diverse excretory systems are variations on
tubular theme
•  Key functions of most excretory systems
–  Filtration: Filtering of body fluids
•  Excretory systems regulate solute movement
between internal fluids and the external
environment
–  Reabsorption: Reclaiming valuable solutes
–  Secretion: Adding nonessential solutes and
wastes from the body fluids to the filtrate
–  Excretion: Processed filtrate containing
nitrogenous wastes, released from the body
33
Figure 44.10
34
Figure 44.10
1 Filtration
Capillary
Filtrate
Excretory
tubule
2 Reabsorption
3 Secretion
Survey of Excretory Systems
•  Systems that perform basic excretory functions
vary widely among animal groups
•  They usually involve a complex network of
tubules
Urine
4 Excretion
9
Figure 44.10
Protonephridia
•  A protonephridium is a network of dead-end
tubules connected to external openings
•  The smallest branches of the network are
capped by a cellular unit called a flame bulb
•  These tubules excrete a dilute fluid and function
in osmoregulation
Flat worms
•  E.g. Flat worms
38
Figure 44.10
Metanephridia
•  Each segment of an earthworm has a pair of
open-ended metanephridia
•  Metanephridia consist of tubules that collect
coelomic fluid and produce dilute urine for
excretion
Earth
worms
40
10
Malpighian Tubules
Malpighian Tubules
l 
Extension of digestive system
l 
In insects and other terrestrial arthropods,
Malpighian tubules remove nitrogenous wastes
from hemolymph and function in osmoregulation
l 
•  Waste molecules and K+ are secreted into tubules
Insects produce a relatively dry waste matter,
mainly uric acid, an important adaptation to
terrestrial life
by active transport
•  Create an osmotic gradient that draws water into
the tubules by osmosis
•  Most of the water and K+ is then reabsorbed into
the open circulatory system through hindgut
epithelium
41
42
Kidneys
Insects
•  Kidneys, the excretory organs of vertebrates,
function in both excretion and osmoregulation
43
44
11
Figure 44.14a
Figure 44.14b
Excretory Organs
Kidney Structure
Renal
cortex
Posterior
vena cava
Renal
medulla
Renal
artery
and vein
Renal
artery
Kidney
Renal
vein
Aorta
Ureter
Ureter
Urinary
bladder
Renal pelvis
Urethra
Figure 44.14c
Figure 44.14d
Nephron Types
Cortical
nephron
Juxtamedullary
nephron
Afferent arteriole
from renal artery Glomerulus
Bowman s capsule
Nephron Organization
Proximal
tubule
Peritubular
capillaries
Distal
tubule
Efferent
arteriole
from
glomerulus
Renal
cortex
Renal
medulla
Collecting
duct
Branch of
renal vein
Vasa
recta
Descending
limb
Loop
of
Henle
Ascending
limb
12
Figure 44.14e
Excretory Organs
l 
Vertebrate kidneys
•  Create a tubular fluid by filtering the blood under
pressure through the glomerulus
•  Filtrate contains many small molecules, in addition
to water and waste products
200 µm
•  Most of these molecules and water are
reabsorbed into the blood
• Selective reabsorption provides great flexibility
Blood vessels from a human kidney.
Arterioles and peritubular capillaries
appear pink; glomeruli appear yellow.
•  Waste products are eliminated from the body in
the form of urine
50
Vertebrate Kidney
l 
l 
l 
l 
Made up of thousands of repeating units –
nephrons
Although the same basic design has been
retained in all vertebrate kidneys, a few
modifications have occurred
All vertebrates can produce a urine that is
isotonic or hypotonic to blood
Only birds and mammals can make a hypertonic
urine
51
52
13
From Blood Filtrate to
Urine
Proximal Tubule
From Blood Filtrate to
Urine
Proximal Tubule
l 
Reabsorption of ions, water, and nutrients takes
place in the proximal tubule
l 
Some toxic materials are actively secreted into the
filtrate
l 
Molecules are transported actively and passively
from the filtrate into the interstitial fluid and then
capillaries
l 
As the filtrate passes through the proximal tubule,
materials to be excreted become concentrated
Figure 44.15
Proximal tubule
Distal tubule
NaCl Nutrients
H2 O
HCO3K+
NaCl
Filtrate
H+
NH3
H2 O
K+
HCO3-
H+
CORTEX
Loop of
Henle
OUTER
MEDULLA
H2 O
NaCl
NaCl
Collecting
duct
Key
Active transport
Passive transport
Urea
NaCl
H2 O
INNER
MEDULLA
14
Limb of the
Loop of Henle
Descending
l 
Reabsorption of water continues through
channels formed by aquaporin proteins
l 
Movement is driven by the high osmolarity of the
interstitial fluid, which is hyperosmotic to the
filtrate
l 
The filtrate becomes increasingly concentrated
Ascending Limb of the Loop of Henle
l 
In the ascending limb of the loop of Henle, salt
but not water is able to diffuse from the tubule
into the interstitial fluid
l 
The filtrate becomes increasingly dilute
Distal Tubule
l 
The distal tubule regulates the K+ and NaCl
concentrations of body fluids
l 
The controlled movement of ions contributes
to pH regulation
Animation: Loop of Henle and Distal
Tubule
Right-click slide / select Play
15
Collecting Duct
l 
The collecting duct carries filtrate through the
medulla to the renal pelvis
l 
One of the most important tasks is reabsorption
of solutes and water
l 
Urine is hyperosmotic to body fluids
Animation: Collecting Duct
Right-click slide / select Play
Solute Gradients & Water
Conservation
l 
The mammalian kidney s ability to conserve
water is a key terrestrial adaptation
l 
Hyperosmotic urine can be produced only
because considerable energy is expended to
transport solutes against concentration
gradients
l 
The two primary solutes affecting osmolarity are
NaCl and urea
The Two-Solute Model
l 
In the proximal tubule, filtrate volume
decreases, but its osmolarity remains the same
l 
The countercurrent multiplier system
involving the loop of Henle maintains a high
salt concentration in the kidney
l 
This system allows the vasa recta to supply the
kidney with nutrients, without interfering with
the osmolarity gradient
16
The Two-Solute Model
The Two-Solute Model
l 
Considerable energy is expended to maintain the
osmotic gradient between the medulla and cortex
l 
Urea diffuses out of the collecting duct as it
traverses the inner medulla
l 
The collecting duct conducts filtrate through the
osmolarity gradient, and more water exits the
filtrate by osmosis
l 
Urea and NaCl form the osmotic gradient that
enables the kidney to produce urine that is
hyperosmotic to the blood
Figure 44.16-2
300
Osmolarity
of interstitial
fluid
(mOsm/L)
300
300
300
Osmolarity
of interstitial
fluid
(mOsm/L)
300
100
300
100
300
CORTEX
H2 O
H2 O
CORTEX
400
400
H2 O
H2 O
OUTER
MEDULLA
H2 O
600
OUTER
MEDULLA
600
H2 O
H2 O
Key
Active
transport
Passive
transport
INNER
MEDULLA
400
NaCl
H2 O
NaCl
H2 O
900
900
Key
1,200
1,200
Active
transport
Passive
transport
INNER
MEDULLA
NaCl
H2 O
600
H2 O
200
400
400
600
700
900
NaCl
H2 O
H2 O
300
NaCl
H2 O
900
NaCl
NaCl
1,200
1,200
17
Figure 44.16-3
300
300
100
300
100
H2 O
400
NaCl
300
300
400
400
H2 O
NaCl
H2 O
CORTEX
200
H2 O
NaCl
H2 O
H2 O
NaCl
NaCl
H2 O
OUTER
MEDULLA
Adaptations of Vertebrate
Kidney
Osmolarity
of interstitial
fluid
(mOsm/L)
600
NaCl
400
600
The form and function of nephrons in various
vertebrate classes are related to requirements for
osmoregulation in the animal s habitat
600
H2 O
NaCl
H2 O
H2 O
l 
Urea
H2 O
Key
Active
transport
Passive
transport
INNER
MEDULLA
H2 O
900
NaCl
700
NaCl
H2 O
900
Urea
H2 O
Urea
1,200
1,200
1,200
70
Mammals
Birds & Other Reptiles
•  The juxtamedullary nephron is key to water
conservation in terrestrial animals
•  Birds have shorter loops of Henle but conserve
water by excreting uric acid instead of urea
•  Mammals that inhabit dry environments have
long loops of Henle, while those in fresh water
have relatively short loops
•  Other reptiles have only cortical nephrons but
also excrete nitrogenous waste as uric acid
71
72
18
Fresh Water Fishes &
Amphibians
Marine Bony Fishes
•  Freshwater fishes conserve salt in their distal
tubules and excrete large volumes of dilute
urine
•  Marine bony fishes are hypoosmotic compared
with their environment
•  Kidney function in amphibians is similar to
freshwater fishes
•  Their kidneys have small glomeruli and some
lack glomeruli entirely
•  Amphibians conserve water on land by
reabsorbing water from the urinary bladder
•  Filtration rates are low, and very little urine is
excreted
73
74
Figure 44.18
Homeostasis
•  Mammals control the volume and osmolarity of
urine
•  The kidneys of the South American vampire bat
can produce either very dilute or very
concentrated urine
•  This allows the bats to reduce their body weight
rapidly or digest large amounts of protein while
conserving water
75
19
Antidiuretic Hormone
Thirst
Osmoreceptors in
hypothalamus trigger
release of ADH.
Hypothalamus
ADH
•  The osmolarity of the urine is regulated by
nervous and hormonal control
Pituitary
gland
•  Antidiuretic hormone (ADH) makes the
collecting duct epithelium more permeable to
water
STIMULUS:
Increase in blood
osmolarity (for
instance, after
sweating profusely)
•  An increase in osmolarity triggers the release of
ADH, which helps to conserve water
Homeostasis:
Blood osmolarity
(300 mOsm/L)
77
Osmoreceptors in
hypothalamus trigger
release of ADH.
Thirst
Hypothalamus
Drinking reduces
blood osmolarity
to set point.
ADH
Increased
permeability
Distal
tubule
H2O reabsorption helps
prevent further
osmolarity
increase.
Pituitary
gland
STIMULUS:
Increase in blood
osmolarity (for
instance, after
sweating profusely)
•  Binding of ADH to receptor molecules leads to a
temporary increase in the number of aquaporin
proteins in the membrane of collecting duct
cells
Collecting duct
Homeostasis:
Blood osmolarity
(300 mOsm/L)
80
20
Renin - Angiotensin System
Renin - Angiotensin System
•  The renin-angiotensin-aldosterone system
(RAAS) is part of a complex feedback circuit that
functions in homeostasis
•  Angiotensin II
–  Raises blood pressure and decreases blood
flow to the kidneys
•  A drop in blood pressure near the glomerulus
causes the juxtaglomerular apparatus (JGA) to
release the enzyme renin
•  Renin triggers the formation of the peptide
angiotensin II
–  Stimulates the release of the hormone
aldosterone, which increases blood volume
and pressure
81
Liver
82
Figure 44.22-3
Angiotensinogen
JGA
releases
renin.
Liver
Angiotensinogen
JGA
releases
renin.
Distal
tubule
Renin
Angiotensin I
Angiotensin I
ACE
Angiotensin II
Distal
tubule
Renin
ACE
Juxtaglomerular
apparatus (JGA)
STIMULUS:
Low blood volume
or blood pressure
(for example, due
to dehydration or
blood loss)
Angiotensin II
Adrenal gland
Aldosterone
Na+
Homeostasis:
Blood pressure,
volume
Juxtaglomerular
apparatus (JGA)
More
and H2O
are reabsorbed in
distal tubules,
increasing blood volume.
Arterioles
constrict,
increasing
blood
pressure.
STIMULUS:
Low blood volume
or blood pressure
(for example, due
to dehydration or
blood loss)
Homeostasis:
Blood pressure,
volume
21
Figure 44.UN01a
Homeostatic Control of the
Kidney
•  ADH and RAAS both increase water
reabsorption, but only RAAS will respond to a
decrease in blood volume
•  Another hormone, atrial natriuretic peptide
(ANP), opposes the RAAS
Animal
Freshwater
fish. Lives in
water less
concentrated
than body
fluids; fish
tends to gain
water, lose salt
•  ANP is released in response to an increase in
blood volume and pressure and inhibits the
release of renin
Inflow/Outflow
Does not drink water
H2O in
Salt in
(active transport by gills)
Urine
Large volume
of urine
Urine is less
concentrated
than body
fluids
Salt out
85
Figure 44.UN01b
Figure 44.UN01c
Animal
Inflow/Outflow
Marine bony
fish. Lives in
water more
concentrated
than body
fluids; fish
tends to lose
water, gain salt
Drinks water
Salt in H2O out
Urine
Small volume
of urine
Urine is
slightly less
concentrated
than body
fluids
Salt out (active
transport by gills)
Animal
Terrestrial
vertebrate.
Terrestrial
environment;
tends to lose
body water
to air
Inflow/Outflow
Drinks water
Salt in
(by mouth)
H2O and
salt out
Urine
Moderate
volume
of urine
Urine is
more
concentrated
than body
fluids
22