osmoregulatory functions of vertebrate kidney

1. Prepared by: Pradip Subedi

3.  Body fluid concentration=surrounding
medium concentration, eg-most marine
animals.
This type of animals never face the problem of
osmoregulation.

4. Animals lives in lower salt concentration are
called hypotonic animals,
In this animals, the water continuously enters into
their bodies and dilute their body fluids, they
have to develop special mechanisms to get rid
of the excess water that enters into their bodies.
Eg- fresh water fishes

5.  Animals that lives in a medium of higher salt
concentration is called hypertonic animals.
In this animals, the water continuously loss from
their body and face a danger of dehydration. ,
they have to develop special mechanisms to get
rid of the dehydration.
Eg- marine bony fishes

6.  Osmo regulation is the process which regulates the
concentration and osmotic pressure of blood by
regulating the water contents of blood plasma. It is
an important process as excessive loss of water
may cause dehydration whereas excess of water
intake may dilute the body fluids.
 There is always an osmotic challenge in animals
due to different medium they live, temperature,
diet and weather conditions, to cope with it some
osmoregulatory mechanism is intiated to maintain
the optimum concentration.

7. The vertebrate kidney is extremely flexible in its
working. It excretes large amount of hypotonic
urine when water intake is very high, while it
excretes small amount of hypertonic urine
when water is deficient and needs to be
conserved.

8.  All animals that live in fresh water must cope
with a continual inflow of water from their
hypotonic environment. In order to maintain
homeostasis of its fluid, the freshwater fish
develops some special osmoregulatory
mechancism to excrete excess amount of water.

9. active
passive
H2O
Na+, Cl-
Na+, Cl-
Drink less
water
kidneys
Ion exchange
pumps; beta chloride cells

11.  Unlike of fresh water animals, marine animals
a continual loss of water to their hypertonic
environment. In order to maintain homeostasis
of its fluid, the marine animals develops some
special osmoregulatory mechancism to prevent
from dehydration

12. drink
active tran.
passive diff.
Na+, Cl-
Mg++, SO4
=
H2O
Na+, Cl-
Na+, Cl-
chloride cells
Mg++, SO4
=
kidneys

14.  Marine sharks and most other cartilaginous fishes
(chondrichthyans) use a different osmoregulatory
“strategy.”
 Unlike bony fishes, marine sharks do not
experience a continuous osmotic loss because high
concentrations of urea and trimethylamine oxide
(TMAO) in body fluids leads to an osmolarity
slightly higher than seawater.
 TMAO protects proteins from damage by urea.
 Consequently, water slowly enters the shark’s body
by osmosis and in food, and is removed in urine

15.  Fresh water which contains a small percentage of salts
diffuses into the body through smooth skin of
amphibians. The well developed glomerular kidneys
serves to remove the excess water which is excreted as
dilute urine. The salts lost through the urine are
replenish by reabsorption of ions from the urine.
 When in water, the frog's bladder quickly fills up
with a hypotonic urine.
 On land, this water is reabsorbed into the blood
helping to replace water lost through evaporation
through the skin.
 The reabsorption is controlled by a hormone similar to
mammalian ADH.

17.  Many reptiles live in dry environments (e.g.,
rattlesnakes in the desert). Among the many
adaptations to such environments is their ability
to convert waste nitrogen compounds into uric
acid.
 Uric acid is quite insoluble and so can be
excreted using only a small amount of water.
Thus we find that reptile glomeruli are quite
small and, in fact, some reptiles have no
glomeruli at all.

19.  Bird kidneys function like those of reptiles
(from which they are descended). Uric acid is
also their chief nitrogenous waste.
 Most birds have a limited intake of fresh water.
However, they need filter only enough to wash
a slurry of uric acid into the cloaca where
enough additional water is reclaimed to
convert the uric acid into a semisolid paste. (It
is the whitish material that pigeons leave on
statues.)

20.  Mammals consists of highly developed kidney
for osmoregulatory purposes.
 Nephrons and associated blood vessels are the
functional units of the mammalian kidney
 The mammalian kidney’s ability to conserve
water is a key terrestrial adaptation

22.  When this condition arises, the urine passed
out of the body is more dilute or hypotonic
than the body fluids to expel the excess of
water. This is because excess of water in the
body fluids lowers the osmotic pressure of the
blood and increases the blood volume. These
changes disturbs the exchange of materials
between the blood pressure and causes
cardiovascular dysfunctioning respectively

23.  It involves 2 processes. They are:
a) Ultra filtration
b) Decreased reabsorption.

24.  Ultra filtration is increased due to the increase
in hydrostatic pressure due to the excess of
water. So more nephric filtrate is filtered out
from the glomerular capillaries into Bowman's
capsule.

25.  Water is mainly reabsorbed through the collecting
tubules. The permeability of the wall of the DCT and
collecting tubules is controlled by anti - diuretic
hormone or ADH or vasopressin hormone which is
released from the posterior lobe of the pituitary gland.
Excess of water in the body fluids signals to posterior
pituitary to stop the release of the hormone
vasopressin. Deficiency of this hormone lowers the
permeability of the cells of the distal convoluted tubule
and the collecting duct, decreasing the reabsorption of
Na+ from the filtrate continues in these regions of the
nephrons.
 More filtration combined with less reabsorption of
water produces abundant dilute urine and this brings
down the volume of body fluids to normal.

26.  When the volume of body fluids decreases below
normal due to profuse sweating during heavy
exercise or high temperature or excessive bleeding
or a prolonged delay in fluid intake, the rate of ultra
filtration is decreased due to decreased blood
volume and low hydrostatic pressure of blood in
the glomerular capillaries and rate of reabsorption
of water is increased by increasing the permeability
of the wall of DCT and collecting tubules due to
increased release of ADH from the posterior
pituitary.
 Less ultrafiltration and more reabsorption produce
small amount of hypertonic urine which increases
body fluid volume to normal.

27. Four process occurs:-
a) filtration — fluid portion of blood (plasma) is
filtered from a nephron (functional unit of
vertebrate kidney) structure known as the
glomerulus into Bowman's capsule or
glomerular capsule (in the kidney's cortex) and
flows down the proximal convoluted tubule to
a "u-turn" called the Loop of Henle (loop of the
nephron) in the medulla portion of the kidney.

28. b) Reabsorption — most of the viscous glomerular
filtrate is returned to blood vessels that
surround the convoluted tubules.
c) Secretion — the remaining fluid becomes urine,
which travels down collecting ducts to the
medullary region of the kidney.
d) Excretion — the urine (in mammals) is stored
in the urinary bladder and exits via the urethra;
in other vertebrates, the urine mixes with other
wastes in the cloaca before leaving the body
(frogs also have a urinary bladder).

30. Key
Active
transport
Passive
transport
INNER
MEDULL
A
OUTER
MEDULL
A
H2O
CORTEX
Filtrate
Loop of
Henle
H2O K+HCO3
–
H+ NH3
Proximal tubule
NaCl Nutrients
Distal tubule
K+ H+
HCO3
–
H2O
H2O
NaCl
NaCl
NaCl
NaCl
Urea
Collecting
duct
NaCl

31. •Smooth muscle cells of
afferent and efferent
arterioles are swoolen and
glanural called
juxtaglomerular cells.
• epithelial cells of DCT in
contact with afferant and
efferent artiole: Macula
densa
•Macula densa +
juxtaglomerular cells=
juxtaglomerular apparatus
which secretes renin
•Renin is associated with
the concersion of
angiotensinogen into
angiotensin influences the
reabsorption of sodium ion
from DCT and water from
collecting tubules

32. Reabsorbed nutrient
 Glucose (100%), amino
acids (100%), bicarbonate
(90%), Na+ (65%), Cl−,
phosphate and H2O (65%)
Notes
 PTH will inhibit
phosphate excretion
 AT II stimulates Na+, H2O
and HCO3
− reabsorption.

33. Reabsorbed nutrient
 H2O
Notes
 Reabsorbtion makes
urine hypertonic.

34. Reabsorbed nutrients
 Na+ (10–20%), K+, Cl−;
indirectly induces para
cellular reabsorption of
Mg2+, Ca2+
Notes
 This region is
impermeable to H2O
and the urine becomes
less concentrated as it
ascends.

35.  Reabsorbed nutrients
 Na+, Cl−
Notes
 PTH causes Ca2+
reabsorption.

36. Nutrients reabsorbed
 Na+(3–5%), H2O
Notes
 Na+ is reabsorbed in
exchange for K+, and
H+, which is regulated
by aldosterone.
 ADH acts