Question

Vitellogenesis in birds full notes

Answer 1

Answer:

VITELLOGENESIS is the process through which food is progressively stored in the growing oocytes of oviparous animals, making up the yolk of the mature egg. The process is remarkably similar in all animals analyzed so far. There are many common points during the vitellogenesis of worms, insects and vertebrates (amphibians, reptiles and birds):

• Most of the food reserves are producced outside the oocytes and transported through the body fluids (pseudocoelomic fluid in nematodes, hemolymph in insects or blood in vertebrates) by soluble proteins.
• The uptake of these proteins by the oocytes is mediated by specific receptors.
• The synthesis of these proteins is controled by hormones (except in nematodes).
• The main proteins involved in the process are called VITELLOGENINS. They are large proteins (greater than 500 kDa or 500,000 times the mass of a Hydrogen atom!) and have lipids, carbohydrates and phosphate associated to them.

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Answer 2

Answer:

The changes in the cytoplasmic and nuclear occur during oogenesis, the yolk material is accumulated by the oocyte, this phase of oogenesis is called vitellogenesis.

Explanation:

• Yolk deposited on reptile and bird eggs is required for embryonic development and growth.
• It is now well known that yolk is synthesized and excreted primarily by the liver under the influence of estrogen produced by the walls of mature follicles and then transported to oocytes.
• Little is known about the factors that regulate its transport and uptake into oocytes.
• However, the yolk deposits in the egg cytoplasm as a very complex individual object, both morphologically and chemically.
• The basic mechanism of yolk formation is similar in reptiles and birds, but the morphology and chemistry of yolks differ not only between reptiles and birds but also between different species depending on their reproductive mode.
• The precise significance of these differences during embryogenesis remains to be determined.

Hence, the stage when the yolk is accumulated is called vitellogenesis.

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