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The egg cell or ovum (pl.: ova) is the female reproductive cell, or gamete, [1] in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is not capable of movement (non- motile ).
The egg cell is generally asymmetric, having an animal pole (future ectoderm). It is covered with protective envelopes, with different layers. The first envelope – the one in contact with the membrane of the egg – is made of glycoproteins and is known as the vitelline membrane (zona pellucida in mammals).
An oocyte (/ ˈ oʊ ə s aɪ t /, oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell (PGC), which then undergoes mitosis ...
The zona pellucida is an extracellular matrix that surrounds the plasma membrane of the egg cell. It helps protect the egg, and has an essential role in fertilization by sperm. It is surrounded by the corona radiata. The corona is composed of cells that care for the egg when it is emitted from the ovary. [1]
The amnion (pl.: amnions or amnia) is a membrane that closely covers human and various other embryos when they first form. It fills with amniotic fluid, which causes the amnion to expand and become the amniotic sac that provides a protective environment for the developing embryo.
The embryo forms a disc of cells, called a blasto-disc, on top of the yolk. Discoidal cleavage is commonly found in monotremes, birds, reptiles, and fish that have telolecithal egg cells (egg cells with the yolk concentrated at one end). The layer of cells that have incompletely divided and are in contact with the yolk are called the "syncytial ...
The innermost membrane of all animal eggs except some cnidarians is called the vitelline membrane. Some invertebrates and some lower chordate eggs are covered by this membrane only, while most have other membranes. [10] Frog and bird eggs have a very thin vitelline membrane which are surrounded by either a jelly layer (frogs) or other membranes ...
In the ovaries, the developing egg cells (or oocytes) mature in the fluid-filled follicles. Typically, only one oocyte develops at a time, but others can also mature simultaneously. Follicles are composed of different types and number of cells according to the stage of their maturation, and their size is indicative of the stage of oocyte ...