Discuss on evolution of urogenital system in vertebrates
Answers
Vertebrate kidneys consist of glomeruli, tubules surrounded by peritubular capillaries, & longitudinal ducts. Variations in
kidney structure among vertebrates are primarily in the number & arrangement of the glomeruli & tubules.
Glomeruli are masses of capillaries that (along with Bowman's capsule) 'filter' the blood - the first step in eliminating waste products from the blood.
Kidney tubules collect the glomerular filtrate & conduct it to a longitudinal duct. Tubules consist of several segments & begin as a Bowman’s (or glomerular) capsule. A glomerulus plus its surrounding Bowman's capsule is called a renal corpuscle.
Longitudinal ducts = begin developing at anterior end of kidney & grow caudally until opening into the cloaca
The urogenital system as a cohesive functional unit probably evolved very early in vertebrate history. Hagfishes and lampreys have separate systems for reproduction and excretion. More derived groups of fishes use kidney tubules and ducts for sperm delivery outside the body (Helfman et al. 2009).
The vertebrate nephron may be homologous to the invertebrate nephridia (Ruppert 1994). The genetics underlying the development of vertebrate female reproductive organs shows many homologies with invertebrate reproductive organs (Kobayashi and Behringer 2003)
I would hypothesize that the both the reproductive and extrectory systems of vertebrates show corresponding homologies to invertebrate organ systems (at least genetic and developmental homologies) but evolution of the urogenital organ system did not evolve until the early vertebrates.