Urinary system

Zaib-Ur-RehmanLecturer 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 mammaliannephron and other is reptilian nephron).

Renal portal system

Uric acid (in mammals urine is made up ofurea while in case of birds it is composedof 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 1\2 to 2\3 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 AcidAmmonia

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 presenceof 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 thenephron and thus they failed to concentrate the urine

These nephrons are located in the cortex of thekidney

In contrast to reptilian nephron, the mammaliannephron is capable of concentrating the urinebecause they possess the loop of henle. Thesenephrons 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 nephronsaccording 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 reabsorptionoccurs from the PCT as a result of this osmotic gradient.


As the filtrate enters the descending limb of the loop of henle, especially in juxtamedullarynephrons 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 vasarecta 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 antidiuresisaccording 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

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