Metabolic waste and Excretory Organ of Animals

Metabolic waste and Excretory Organ of Animals

Evolutionary Types of Vertebrate Kidney

Pronephric kidney

Nephron has a ciliated funnel, nephrostomes, and the coelomoduct to drain coelomic fluid like invertebrates.

Glomerulus bulges into the coelom near each nephrostome. Due to glomerular pressure plasma filtrate forces into coelomic fluid from where it is drawn into nephrostome. Ex– Embryo or

larval stage of vertebrates.

However, a modified pronephros called head kidney occurs in the adults of Hagfishes.

Mesonephric kidney

Nephric tubule gives out cup-like outgrowth, Bowmann’s capsule on its side lodging the glomerulus. The plasma filtrate enters the nephron through this, and nephrostome is also functional.

Mesonephros is generally accompanied by posterior part of mesomere. It is, therefore, also called opisthonephros. Ex - Pisces and Amphibia.

Metanephric kidney

Coelomoduct and nephrostomes totally disappear and only glomerular filtrate (not the coelomic fluid) passes into nephron.  Ureter is formed separately by metanephric duct. Ex - Reptiles,

Birds & Mammals.

The ducts which drain in the ancestral (or embryonic) nephrons is the Wolffian duct which persists also in adult stage.  In male anamniotes this duct acts as both ureter and sperm duct but

in female anamniotes as ureter.  In male amniotes it remains only as sperm duct since ureter is formed separately by metanephric duct.  The oviduct in females of both amniotes and

anamniotes is formed separately by Mullerian duct.

Bidder’s Canal – It is present in the kidney of male frog. It is helpful in the transfer of sperms from the vasa-efferentia to water.