1 . EXCRETION Waste product removal e.g. nitrogenous – uric acid (mammals urea , fish ammonia)  Kidneys – secrete uric acid (product of protein metabolism)  Gastro-intestinal tract secretions e.g. bile  No sweat glands  Salt glands (water birds)  Water loss – lungs 2. URINARY SYSTEM • Major organs are the kidneys, the ureter and the cloaca. • No urinary bladder in bird. 3 . ANATOMICAL STRUCTURE OF KIDNEY Avian kidneys are paired fitted closely the bony depression on the dorsal wall of the pelvis . Each kidney is divided into three lobes. 4 . 5 . NEPHRON Two kinds of nephrons. 1. Reptilian nephron 2. Mammalian nephron • 6 . • 7. DIFFERENCE BETWEEN AVIAN AND MAMMALIAN KIDNEY 8. RENAL PORTAL SYSTEM Uric acid is formed in the liver as well as the kidneys of the birds from ammonia, which is the most toxic protein metabolic by product . 9. GLOMERULAR FILTRATION  Fluid pressure forces water and dissolved substances from glomerular blood to Bowman’s capsule .  Filtration averages 125 ml/min form two kidneys. 10 . TUBULAR REABSORPTION Return of the useful substances from the filtrate to the blood capillaries or interstitial fluid. 11 . COUNTER CURRENT MECHANISM This mechanism works in the loop of henle to increase water reabsorbed from the descending limb as a result of salt reabsorbed from the ascending limb . 12 . POST RENAL URINE MODIFICATION After the presentation of urine to cloaca their might be retrograde flow or backward flow of urine into the colon. In the colon reabsorption of excessive amount of water as well as sodium ion takes place. 13 . HORMONES RESPONSIBLE FOR URINE FORMATION Arginine vasotocin ,Angiotensin ׀׀ ,Aldosterone ,ANP (arterial natriuretic peptide) Aldosterone is responsible for the reabsorption of sodium and excretion of potassium in the filtrate.

1. EXCRETORY SYSTEM
SUCHISMITA PRADHAN
DIVISION OF POULTRY
SCIENCE

2. EXCRETION
Waste product removal e.g. nitrogenous – uric acid (mammals urea ,
fish ammonia)
 Toxic compounds (with metabolism)
 Homeostasis –
Blood volume/extra-cellular volume
Blood osmolality
Acid - base/Ph
EXCRETORY ORGANS
 Kidneys – secrete uric acid (product of protein metabolism)
 Gastro-intestinal tract secretions e.g. bile
 No sweat glands
 Salt glands (water birds)
 Water loss – lungs

3. URINARY SYSTEM
• Major organs are the kidneys,
the ureter and the cloaca.
• Two kidneys, each with a ureter
that carries the urine produced
by the kidneys to the cloaca
where it leaves the body .
• No urinary bladder in bird.

4. ANATOMICAL FEATURE OF KIDNEY
Avian kidneys are paired fitted closely the bony depression on the
dorsal wall of the pelvis . Each kidney is divided into three
lobes.
1. Cranial lobe
2. Middle lobe
3. Caudal lobe
 Each lobe has Cortical and medullary areas
Cortical = outside
Medullary = inside
 Each lobe is further subdivided into small lobules .
 Kidney tubule or nephron –basic functional unit of the kidney
200,000 in chicken.

5. NEPHRON
1 = Bowman’s capsule
2 = glomerulus,
3 = afferent arteriole
4 = efferent arteriole,
5 = proximal convoluted tubule
6 = distal convoluted tubule
7 = collecting duct
8 = loop of Henle
9 = peritubular capillaries
(or vasa recta)

6. TYPES OF NEPHRON
Two kinds of nephrons.
1. Reptilian nephron
2. Mammalian nephron
Reptilian nephron - loop of henle absent so less
quantity of water is reabsorbed by nephron and
thus they failed to concentrate the urine.
These nephrons are located in the cortex of the kidney .
Mammalian nephron - capable of concentrating the
urine because they possess the loop of henle.
These nephrons are located in the medulla of the
kidney .
 When both are functional 25% filtrate comes from
mammalian type while 75% comes from reptilian
nephrons

7. Contd....
• The tuft of capillaries is known as glumerulus which is
encapsulated or enclosed by bowmann’s capsule.
• Blood is filtered by the glomerulus and the filtrate is taken up
by the bowmann’s capsule
• The filtrate is made up of waste products as well as the useful
products such as water and electrolyte .
• The filtrate from the bowmann’s capsule is passed down to the
proximal convoluted tubules, loop of henle, distal convoluted
tubule and then ultimately to the collecting ducts .
• Passing through the tubular portion of the nephron the useful
substances from the filtrate are taken up by the network of
capillaries which surrounds the nephron.
• The network of capillaries is known as vasa recta .

9. DIFFERENCE BETWEEN AVIAN AND
MAMMALIAN KIDNEY
 Two types of nephron (mammalian nephron and reptilian
nephron)
 Renal portal system
 Uric acid (in mammals urine is made up of urea while in case
of birds it is composed of crystals of uric acid)
 Post renal urine modification

10. RENAL PORTAL SYSTEM
 The unique feature of avian kidney is the presence of renal
portal system which carries the inner portal blood to the
kidney.
 The renal portal blood is the veinous blood that comes to the
kidney from hind limbs, through the external iliac and sciatic
vein.
 The renal portal system supplies 12 to 23 of the blood to the
kidney.
Uric acid is formed in the liver as well as the kidneys of the birds
from ammonia, which is the most toxic protein metabolic by
product .

11. GLOMERULAR FILTRATION
 Fluid pressure forces water and dissolved substances
from glomerular blood to Bowman’s capsule .
 Filtration averages 125 ml/min form two kidneys.
 More than 99% must be returned to the blood .
 Filtration involves the small molecules:
water,electrolytes, urea, glucose, amino acids
 It does not involve the blood proteins or cells.
 The large amount of filtration is the result of the porous
glomerular membrane and filtration slits in the visceral
layer of Bowman's capsule.

12. TUBULAR REABSORPTION
Return of the useful substances from the filtrate to the blood
capillaries or interstitial fluid.
1. NaCl (Active transport)
2. Water (Osmosis) Water is reabsorbed by osmosis. Entering
the proximal convoluted tubule the filtrate is very dilute
compared to the blood. 65% of water reabsorption occurs
from the PCT as a result of this osmotic gradient.
As the filtrate enters the descending limb of the loop of henle of
mammilary nephrons with long loops, it is exposed to
increasingly hypertonic medulla. This pulls at least another
20% of absorbable water out of the filtrate.
3. Glucose, amino acid ( Active Co transport)

13. Reabsorption of materials from the proximal convoluted tubule
back into the blood

14. COUNTER CURRENT MECHANISM
This mechanism works in the loop of henle to increase
water reabsorbed from the descending limb as a result
of salt reabsorbed from the ascending limb .
The term counter current comes from the fact that fluid
is moving in opposite directions in the two limbs of
the loop. This magnifies the effect of transport from
one limb on transport from the other limb.

16. POST RENAL URINE MODIFICATION
After the presentation of urine to cloaca their might be retrograde flow
or backward flow of urine into the colon.
In the colon reabsorption of excessive amount of water as well as
sodium ion takes place.
Initially, the solutes in the urine cause water to move by osmosis out of
the surrounding tissues into the coprodeum .After being transported
by peristalsis into the colon, however, NaCl is transported out of the
colon and water follows the concentration gradient (osmosis) and is
reabsorbed (Laverty and Skadhauge 2008).

17. HORMONES RESPONSIBLE FOR URINE
FORMATION
There are hormones which take part in the formation of urine.
1. Arginine vasotocin
2. Angiotensin ‫׀׀‬
3. Aldosterone
4. ANP (arterial natriuretic peptide)
Angiotensin ‫׀׀‬hormone is responsible for natriuresis and diuresis along
with antinatriuresis and antidiuresis according to the need of water
conservation.
Aldosterone is responsible for the reabsorption of sodium and excretion
of potassium in the filtrate.
ANP is released from the atrium of heart and is responsible for
natriuresis as well as diuresis in case of birds.

18. ARGININE VASOTOCIN
• In response to dehydration, the
pituitary gland releases arginine
vasotocin (AVT) into the blood.
• In the kidneys, AVT causes a
reduction in the glomerular filtration
rate ,so less water moves from the
blood into the kidney tubules.
• AVT increases the permeability of the
walls of collected ducts to water by
opening protein water channels called
aquaporins.

19. REFERENCES
 Strukie’s avian physiology ( fifth edition)
By G.Causey Whittow
 Bradley, OC (1960) The Structure of the Fowl, Tom Grahame
ed, Oliver and Boyd, Edinburgh, UK.
 Dingle, JG (1991) Animal anatomy and Physiology 11(P);
Study Book, DEC, USQ, Toowoomba, Australia.