Read the text, translate it

One of the most interesting and mysterious attributes of life is the ability to reproduce. In people reproduction is sexual. It means that males and females have specialized cells known as germ cells, or gametes. In males they are called spermatozoa and in female they are called ova. Germ cells are characterized by having half as many chromosomes as are found in any other cell in the body. During their formation they go through a special process of cell division, called meiosis [mai'ausis], that in humans reduces the chromosome number from 46 to 23. The female reproductive system consists of organs which produce ova and provide a place for the growth of the embryo.

Ova are produced by the ovary from the puberty period to menopause (end of the fertile period in women). Release of an ovum from the graafian follicle of the ovary into the fallopian tube is called ovulation. Besides the ovaries the major organs of the female reproductive system include the fallopian tubes, uterus, vagina and vulva.

Vulva is the external genitalia, it includes the vaginal lips, clitoris and vaginal and urethral orifices. The space between the vaginal orifice and the anus is called perineum.

Breasts also belong to the reproductive system, as they are milk-producing glands which consist of lactiferous ducts and sinuses, carrying milk to the nipple.

In the female, as in the male, reproductive function is controlled by hormones from pituitary gland as regulated by the hypothalamus. Female activity is cyclic, that is, shows regular periods of increases and decreases in hormone levels. The length of the menstrual cycle varies between 22 and 45 days. The duration of menstrual flow is 2 to 6 days.

Estrogen, progesterone [prs'^sstsraun] are two female sex hormones. Estrogen promotes development of the uterine lining and maintains secondary sex characterics.

Progesterone is produced by the corpus luteum and placenta; maintains the lining of the uterus for pregnancy.

When semen is deposited in the vagina, many spermatozoa immediately wriggle about in all directions. When a spermatozoon encounters an ovum, it can penetrate the cell membrane of the ovum. The result of this union is fertilization.

The placenta is tlie sponge-like vascular organ. It develops during pregnancy in the uterine wall, and the fetus grows in it up to the parturition or delivery,

Menopause is the cessation of menstruation. It is often called change of life. It occurs between the ages of 45 and 55, and is caused by a normal decline in ovarian function.

Date: 2015-09-18; view: 1129; Нарушение авторских прав