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The kidney of the frog is an opisthonephros. The kidneys are seen as two elongated, red organs in this image. The opisthonephros is the functional adult kidney in lampreys (cyclostomes), most fishes, and amphibians. [1] It is formed from the extended mesonephros along with tubules from the posterior nephric ridge. [2]
Each kidney, with its adrenal gland is surrounded by two layers of fat: the perirenal fat present between renal fascia and renal capsule and pararenal fat superior to the renal fascia. The human kidney is a bean-shaped structure with a convex and a concave border. [14]
The pronephros is a functioning kidney of the embryo in bony fish and amphibian larvae, [7] but in mammals it is most often considered rudimentary and not functional. [18] In some lungfish and bony fishes, the pronephros can remain functional in adults, including often simultaneously with the mesonephros. [ 7 ]
In lungfish and tetrapods, the renal portal vein is joined by a vein traveling upwards from the abdominal vein, [4] which can bring venous blood from the hind limbs and ventral body wall into the renal portal system, or alternatively, enable blood from the tail and groin to pass into the hepatic portal system, already served by blood from the gut, via the hepatic portal vein, and from the hind ...
Pronephros is the most basic of the three excretory organs that develop in vertebrates, corresponding to the first stage of kidney development. It is succeeded by the mesonephros, which in fish and amphibians remains as the adult kidney. In amniotes, the mesonephros is the embryonic kidney and a more complex metanephros acts as the adult kidney ...
The mesonephros persists and forms the anterior portion of the permanent kidneys in fish and amphibians, but in reptiles, birds, and mammals, it atrophies and for the most part disappears rapidly as the permanent kidney (metanephros) begins to develop [2] during the sixth or seventh week. By the beginning of the fifth month of human development ...
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis.The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone).
In cartilaginous fish, there is also a shorter duct which drains the posterior (metanephric) parts of the kidney, and joins with the mesonephric duct at the bladder or cloaca. Indeed, in many cartilaginous fish, the anterior portion of the kidney may degenerate or cease to function altogether in the adult. [ 35 ]