Animals Egg cell

1 animals

1.1 human , mammal ova
1.2 ooplasm
1.3 ova development in oviparous animals
1.4 ovoviviparity

animals

in animals, egg cells known ova (singular ovum, latin word ovum meaning egg or egg cell). term ovule in animals used young ovum of animal. in vertebrates, ova produced female gonads (sexual glands) called ovaries. number of ova present @ birth in mammals , mature via oogenesis. white et al. disproved longstanding dogma of ova produced before birth. team vincent center reproductive biology, massachusetts, boston showed oocyte formation takes place in ovaries of reproductive-age women. report challenged fundamental belief, held since 1950s, female mammals born finite supply of eggs depleted throughout life , exhausted @ menopause.

human , mammal ova

diagram of human egg cell



ovum , sperm fusing together



the process of fertilizing ovum (top bottom)

in mammals ovum fertilized inside female body.

the human ova grow primitive germ cells embedded in substance of ovaries. each of them divides repeatedly give secretions of uterine glands, forming blastocyst.

the ovum 1 of largest cells in human body, typically visible naked eye without aid of microscope or other magnification device. human ovum measures approximately 0.1 mm in diameter.

ooplasm

ooplasm (also: oöplasm) yolk of ovum, cell substance @ center, contains nucleus, named germinal vesicle, , nucleolus, called germinal spot.

the ooplasm consists of cytoplasm of ordinary animal cell spongioplasm , hyaloplasm, called formative yolk; , nutritive yolk or deutoplasm, made of rounded granules of fatty , albuminoid substances imbedded in cytoplasm.

mammalian ova contain tiny amount of nutritive yolk, nourishing embryo in stages of development only. in contrast, bird eggs contain enough supply chick nutriment throughout whole period of incubation.

ova development in oviparous animals

in oviparous animals (all birds, fish, amphibians , reptiles) ova develop protective layers , pass through oviduct outside of body. fertilized male sperm either inside female body (as in birds), or outside (as in many fish). after fertilization, embryo develops, nourished nutrients contained in egg. hatches egg, outside mother s body. see egg discussion of eggs of oviparous animals.

the egg cell s cytoplasm , mitochondria sole means egg able reproduce mitosis , form blastocyst after fertilization.

ovoviviparity

there intermediate form, ovoviviparous animals: embryo develops within , nourished egg in oviparous case, hatches inside mother s body shortly before birth, or after egg leaves mother s body. fish, reptiles , many invertebrates use technique.