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For other uses, see Ovum (disambiguation).An ovum (plural ova) is a haploid female reproductive cell or gamete.The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization.In lower plants and algae, the ovum is also often called oosphere.Ova production
In higher animals, ova are produced by female gonads (sexual glands) called ovaries and all of them are present at birth in mammals, and mature via oogenesis.In the viviparous animals (which include humans and all other placental mammals), the ovum is fertilized inside the female body, and the embryo then develops inside the uterus, receiving nutrition directly from the mother.The ovum is the largest cell in the human body, typically visible to the naked eye without the aid of a microscope or other magnification device.Upon maturation, the neck opens to allow sperm cells to swim into the archegonium and fertilize the egg.They are fertilized by male sperm either inside the female body (as in birds), or outside (as in many fishes).The egg cell's cytoplasm and mitochondria (and chloroplasts in plants) are the sole means of the egg being able to reproduce by mitosis and eventually form a blastocyst after fertilization.Ovoviviparity
There is an intermediate form, the ovoviviparous animals: the embryo develops within and is nourished by an egg as in the oviparous case, but then it hatches inside the mother's body shortly before birth, or just after the egg leaves the mother's body.The Ovum, Gray's Anatomy of the Human Body, Yahoo!All text is available under the terms of the GNU Free Documentation License.And remember you are not alone.What is a blighted ovum?How do I know if I am having or have had a blighted ovum?It is possible that you may have minor
abdominal cramps, minor vaginal spotting or bleeding.What causes a blighted ovum?This can be caused by abnormal cell division,
or poor quality sperm or egg.This is a decision only you can make for yourself.How can a blighted ovum be prevented?Unfortunately, in most cases a blighted ovum cannot be prevented.Some couples will seek out genetic testing if multiple early pregnancy
loss occurs.For specific medical advice, diagnosis, and treatment, consult your doctor.Definition of OvumOvum: An egg in the ovary of the female.It combines with the male
gamete, called a sperm, to form a zygote.From the Doctors at MedicineNet.Learn about Down syndrome, the most common cause of mental retardation.Get tips and advances in treatment.MedicineNet provides reliable doctor produced health and medical information.Win a Wii Fit from WebMD.Test your Health IQ for a chance to win!We comply with the HONcode standard for health trust worthy information: verify here.Columbia Encyclopedia
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Shaw, G.Human ova are extremely minute, measuring about 0.By the enlargement and subsequent rupture of a follicle at the surface of the ovary, an ovum is liberated and conveyed by the uterine tube to the cavity of the uterus.Unless it be fertilized it undergoes no further development and is discharged from the uterus, but if fertilization take place it is retained within the uterus and is developed into a new being.In appearance and structure the ovum (Fig.The ovum is enclosed within a thick, transparent envelope, the zona striata or zona pellucida, adhering to the outer surface of which are several layers of cells, derived from those of the follicle and collectively constituting the corona radiata.Human ovum examined fresh in the liquor folliculi.The zona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata.The egg itself shows a central granular deutoplasmic area and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot.In the mammalian ovum the nutritive yolk is extremely small in amount, and is of service in nourishing the embryo in the early stages of its development only, whereas in the egg of the bird there is sufficient to supply the chick with nutriment throughout the whole period of incubation.The nutritive yolk not only varies in amount, but in its mode of distribution within the egg; thus, in some animals it is almost uniformly distributed throughout the cytoplasm; in some it is centrally placed and is surrounded by the cytoplasm; in others it is accumulated at the lower pole of the ovum, while the cytoplasm occupies the upper pole.The germinal vesicle or nucleus is a large spherical body which at first occupies a nearly central position, but becomes eccentric as the growth of the ovum proceeds.The zona striata or zona pellucida (Fig.It is not yet determined whether the zona striata is a product of the cytoplasm of the ovum or of the cells of the corona radiata, or both.The cells of the corona radiata soon disappear; in some animals they secrete, or are replaced by, a layer of adhesive protein, which may assist in protecting and nourishing the ovum.The phenomena attending the discharge of the ova from the follicles belong more to the ordinary functions of the ovary than to the general subject of embryology, and are therefore described with the anatomy of the ovaries.Before an ovum can be fertilized it must undergo a process of maturation or ripening.This takes place previous to or immediately after its escape from the follicle, and consists essentially of an unequal subdivision of the ovum (Fig.Three of the four cells are small, incapable of further development, and are termed polar bodies or polocytes, while the fourth is large, and constitutes the mature ovum.This applies not only to the somatic cells but to the primitive ova and their descendants.For the purpose of illustrating the process of maturation a species may be taken in which the number of nuclear chromosomes is four (Fig.If an ovum from such be observed at the beginning of the maturation process it will be seen that the number of its chromosomes is apparently reduced to two.During the metaphase (see page 37) each tetrad divides into two dyads, which are equally distributed between the nuclei of the two cells formed by the first division of the ovum.Formation of polar bodies in Asterias glacialis.In III the elevation is constricted off, forming the first polar body (pb1), and a second spindle is formed.In IV is seen a second elevation which in V has been constricted off as the second polar body (pb2).Out of the remainder of the spindle (f.VI) the female pronucleus is developed.Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum.This second division is also unequal, producing a large cell which constitutes the mature ovum, and a small cell, the second polar body.The first polar body frequently divides while the second is being formed, and as a final result four cells are produced, viz.The nucleus of the mature ovum is termed the female pronucleus.Click here to shop the Bartleby Bookstore.Blighted ovum: What are the causes?What causes a blighted ovum?Blighted ovum is often due to chromosomal abnormalities in the fertilized egg.With a blighted ovum, you may miss a period and have a positive pregnancy test.This is because the placenta secretes human chorionic gonadotropin (HCG), a pregnancy hormone.But later when the placenta stops growing and hormone levels decrease, your pregnancy symptoms will subside.At this point, you may have minor abdominal cramping and light spotting or bleeding.Another option is a procedure called D and C (dilation and curettage) to remove the placental tissues.If you have consecutive miscarriages in the first trimester, your doctor may recommend testing to try to determine the cause.URI('Blighted ovum: What are the causes?LEGAL CONDITIONS AND TERMS OF USE APPLICABLE TO ALL USERS OF THIS SITE."Blighted ovum: What are the causes?"
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