Urinary system

Zaib-Ur-Rehman
Lecturer Poultry Science
PMAS-AAUR, Pakistan

 Why?
 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
Department of Poultry Science

 Kidneys – secrete uric acid = product of protein
metabolism, etc.
 Gastro-intestinal tract secretions e.g. bile
 No sweat glands
 Salt glands (water birds)
 Water loss - lungs

 Paired kidney
 Ureters
 Cloaca/vent

 To filter the blood and removal of waste products
 Reabsorption of useful material such as
electrolyte and excessive amount of water

 Two types of nephron (one is mammalian
nephron and other is 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

 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.

 The urine of birds is made up of uric acid instead
of urea which is the metabolic products of
proteins and amino acids. It is the least toxic
protein by product which can be excreted with
minute quantities of water
 The 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

 Birds - Nitrogenous wastes are secreted in the
form of uric acid (not soluble in water).
 Implications for embryo in egg
 Mammals - Nitrogenous wastes are secreted in
the form of urea

Amino Acid
Ammonia
Uric Acid

 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.

 The avian kidneys are paired fitted closely the bony
depression on the dorsal wall of the pelvis The each
kidney is divided into three lobes.
 Cranial lobe
 Middle lobe
 Caudal lobe
 Cortical and medullary areas
 Cortical = outside
 Medullary = inside
 Kidney tubule or nephron –basic functional unit of
the kidney
 200,000 in chicken.
Department of Poultry Science, PMAS UAAR

 The each lobe is further subdivided into small
lobules
 The ureters originate from each kidney and carry
the urine from the kidneys to the cloaca
 The kidney is made up of two parts. The middle
part is known as medulla while outer portion is
known as cortex
 The basic functional and structural unit of kidney
is known as nephron which is made up of
different components

 Nephron is made up of following parts.
 Glomerulus (Filteration)
 Bowman’s capsule
 Afferent arterioles, capillaries, Efferent arteries
 Tubule (Re-absorption)
 Proximal segment
 Loop of Henle (Medullary only)
 Distal segment
 Collecting duct
 Vesa Recta (Re-Absorption to the Blood)

 The tuft of capillaries is known as glumerulus which is
encapsulated or enclosed by glomerulus capsule also known as
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

 The avian kidneys are characterized by the presence
of two kinds of nephrons.
 Reptilian nephron
 Mammalian nephron
 In reptilian nephron the loop of henle is absent due
to which less quantity of water is reabsorbed by the
nephron and thus they failed to concentrate the urine
 These nephrons are located in the cortex of the
kidney
 In contrast to reptilian nephron, the mammalian
nephron is capable of concentrating the urine
because they possess the loop of henle. These
nephrons are located in the medulla of the kidney

 Depending upon the need of water conservation
the avian kidneys can alternatively use the
reptilian and mammalian type nephrons
according to the demand of water
 When both are functional 25% filtrate comes
from mammalian type while 75% comes from
reptilian nephrons

 Retention (Not filtered) - proteins, blood cells
 Filtered 95% of plasma - water, glucose, amino-
acids, sodium (Na+) etc.
 Re-absorbed - water, glucose, amino-acids,
sodium (Na+), K+, Ca++, phosphate, chloride etc.
 Active transport with ATP expended
 Passive (e.g. H2O following ions)
 Counter current mechanism

 Fluid pressure forces water and dissolved substances
 Filtration averages 125 ml/min for your two kidneys
 This amounts to about 180 Liters per day
 Since we urinate an average of 1500 ml per day
 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

 Return of the useful substances from the filtrate
to the blood capillaries or interstitial fluid
 NaCl (Active transport)
 Water (Osmosis)
 Glucose, amino acid ( Active Co transport)

 H2O — pulled by osmosis into Hypertonic blood.
65% occurs in PCT
 NaC1— active transport of either Na+ or C1-, pulls
water along.
 100% of glucose and amino acid transported -occurs
in PCT by active co-transport
 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, especially in juxtamedullary
nephrons with long loops, it is exposed to
increasingly hypertonic medulla. This pulls at
least another 20% of absorbable water out of the
filtrate.
 Reabsorption in this area is termed obligatory
because it must occur due to the osmolarity of
the surrounding interstitial fluid.

 The Countercurrent Multiplier
 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 countercurrent 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.

 The countercurrent exchange of salt in the vasa recta.
 The vasa recta has descending and ascending limbs too_
Blood flowing into the Medulla in the descending limb
picks up salt from the hypertonic medulla
 As the surrounding medullary fluid becomes more and
more salty toward the papilla the gradient increases and
more and more salt is picked up by the descending vasa
recta limb. But as the blood heads back up to the cortex in
the ascending limb of the rasa recta, the interstitial fluid
becomes less and less salty
 This causes the gradient to reverse and salt diffuses back
out of the vasa recta into the medulla. This helps to
conserve salt and keep the medulla hypertonic.

 There are three hormones which take part in the
formation of urine.
 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.

 Ultra filtration: It is a process which takes place
under the pressure and results in the filtration of
blood, within the glomerulus.
 Active Tubular Reabsorption: This process is
characterized by the active reabsorption of useful
substances from the filtrate in the tubular
portion of the nephron.
 Excretion: The process of excretion involves the
removal of uric acid from the body of bird

Urinary system

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Urinary system

Similar to Urinary system (20)

More from mithu mehr

More from mithu mehr (20)

Urinary system

Editor's Notes