ZOO 2090 Lecture Notes - Lecture 18: Somite, Mesonephros, Pronephros
1 May 2018
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ZOO2090 – Diversity in Urinary and Reproductive Systems
Urogenital System:
• The reproductive and excretory systems are intimately associated with each other and it is
easier to combine them in order to understand how they evolved
• In vertebrates, mesomeres (of the mesoderm) give rise to the urogenital organs
Function:
• Excretory system:
o Remove wastes (nitrogenous and other harmful substances)
o Control osmosis (water and salt balance)
Organs involved: kidney, gills, skin, part of digestive system, salt glands
• Reproductive system:
o Produce gametes (and bring them together)
o Provide nourishment to embryo
o Release eggs/young
Organs involved: gonads, ducts, cloaca, copulatory organs
Kidney - developmental origin of the elements of the excretory system
• Development sweeps from anterior to posterior, but the wave is interrupted at two levels
so that the anterior, middle and posterior kidneys form in sequence
o The more anterior regions usually degenerate as posterior regions become more
functional
o The more posterior break may be omitted so that two (instead of three) pairs of
kidneys are formed in sequence
• Division:
o Pronephros
▪ Segmented (usually first four)
▪ Appear in all vertebrates (rudimentary form) and degenerated quickly
▪ Functional in fish larvae and adults of hagfish (and some teleosts)
▪ In other fish, pronephrons degenerated into ‘head kidney’ (an organ
limited to hemopoietic, lymphoid and endocrine functions)
o Opisthonephros
▪ Mesonephros
• Reduced segmentation
• In late larval and adult anamniotes, all or most of the mesomere
posterior to pronephros forms one kidney = opisthonephros
• Among amniotes, the middle part of the nephrogenic cord
develop first called the mesonephros which is only present in
fetuses (it then degenerates)
▪ Metanephros
• Never segmented
• Kidney of amniotes
• Most posterior part of nephrogenic cord that replaces
mesonephros in development
• Dual origin of amniote kidney: origin of the ureter (drains urine)
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Document Summary
Zoo2090 diversity in urinary and reproductive systems. Urogenital system: the reproductive and excretory systems are intimately associated with each other and it is easier to combine them in order to understand how they evolved. In vertebrates, mesomeres (of the mesoderm) give rise to the urogenital organs. Function: excretory system, remove wastes (nitrogenous and other harmful substances, control osmosis (water and salt balance) Organs involved: kidney, gills, skin, part of digestive system, salt glands: reproductive system, produce gametes (and bring them together, provide nourishment to embryo, release eggs/young. In other fish, pronephrons degenerated into head kidney" (an organ limited to hemopoietic, lymphoid and endocrine functions: opisthonephros, mesonephros, reduced segmentation. Functional unit: nephron: nephron = nephric (renal) tubule + renal corpuscle, basic deign is paired and segmented nephric tubules opening on one end (facing glomeruli) then each connecting to the nephric duct. Nephron variation: desert rodents tend to have mostly long tubules loops descending into the medulla.
