Avian excretory system

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 A vian kidneys are paired fitted closely the bony depression on the dorsal wall of the pelvis . Each kidney is divided into three lobes. Cranial lobe Middle lobe Caudal lobe Each lobe has Cortical and medullary areas Cortical = outside Medullary = inside Each lobe is further subdivided into small lobules . K idney 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 T wo kinds of nephrons . Reptilian nephron 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 .

8. 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) P ost renal urine modification

9. 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 1\2 to 2\3 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 .

10. 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.

11. TUBULAR REABSORPTION Return of the useful substances from the filtrate to the blood capillaries or interstitial fluid. NaCl (Active transport) 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)

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

13. COUNTER CURRENT MECHANISM This mechanism works in the loop of h enle 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.

14. 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). 

15. HORMONES RESPONSIBLE FOR URINE FORMATION There are hormones which take part in the formation of urine . Arginine vasotocin Angiotensin ׀׀ Aldosterone 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.

16. 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 .

17. 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.