> In human females at the tim... In human females at the time of birth there are two million ova. How many of them normally reach maturity in the course of normal reproductive life? Each ovary contains approximatley 2 million immature ova which were formed during the first 5 months of intra-uterine life.
Ovum, plural ova, in human physiology, single cell released from either of the female reproductive organs, the ovaries, which is capable of developing into a new organism when fertilized (united) with a sperm cell.
After the egg matures, a second hormone from the pituitary, luteinizing hormone, is liberated; this causes the egg’s release, called ovulation (q.v.). As the ovum develops, the walls of the follicle expand by adding new cells.
A hollow ball of cells, the follicle, encompasseseach ovum. Within the follicle the ovum gradually matures (seeoogenesis). It takes about four months for a follicle to develop once it is activated. Some follicles lie dormant for 40 years before they mature; others degenerate and never develop.
Each ovary contains approximatley 2 million immature ova which were formed during the first 5 months of intra-uterine life. Throughout the life, the vast majority of the follicles will die off through a process called as atresia. Atresia begins at birth and continues throughout the course of the woman's reproductive life.
Each ovary contains approximatley 2 million immature ova which were formed during the first 5 months of intra-uterine life. Throughout the life, the vast majority of the follicles will die off through a process called as atresia. Atresia begins at birth and continues throughout the course of the woman's reproductive life. When the woman reaches puberty and starts to menstruate, only about 400,000 follicles remain. With each menstrual cycle, a thousand follicles are lost and only one lucky little follicle will mature into an ovum, which is released into the fallopian tube, It means out of 1-2 million follicles, only about 400-500 will ever mature.
After the egg matures, a second hormone from the pituitary, luteinizing hormone , is liberated; this causes the egg’s release, called ovulation ( q.v. ). As the ovum develops, the walls of the follicle expand by adding new cells.
During child-bearing years, 300 to 400 follicles mature and emit eggs capable of being fertilized. By the time a woman reaches menopause, most remaining follicles have degenerated. A follicle-stimulating hormone, secreted into the bloodstream by the pituitary, causes ovum growth.
The outer surface of each ovary is covered by a layer of cells (germinal epithelium); these surround the immature egg cells, which are present in the ovaries from the time of birth. A hollow ball of cells, the follicle, encompasses each ovum. Within the follicle the ovum gradually matures ( see oogenesis ).
When the follicle ruptures, the egg is released from the ovary and is then captured and guided by the fallopian tubes. Muscular contractions of the fallopian tubes move the egg to the cavity of the uterus.
The ovum itself has a central nucleus that contains the female’s genetic material; this, with the genetic material in the sperm cell, determines the inherited characteristics of the child. Surrounding the nucleus is a cell plasma, or yolk, that contains nutritional elements essential to the developing egg cell.
After the egg is fertilized it undergoes a series of cell divisions. If at an early stage of its development the fertilized egg splits into two parts that continue to grow, identical twins will result; incomplete division will result in Siamese twins, born physically joined.
In any one human generation, the egg’s development starts before the female that carries it is even born; 8 to 20 weeks after the fetus has started to grow,…