Ovarian Function

Human Physiology

Lesson 27 : Female Reproductive System -I

Ovarian Function

Ovaries in female is regarded as primary sex organ responsible for production of female gamete called ovum and female sex hormones, estrogen and progesterone. Both these functions begin after onset of puberty in female individual.

  1. Gamete Production: Gamete production occurs from mitotic and meiotic cell division of precursor cell called oogonia. Each ovary contains millions of oogonia in fetal female, the number of which is gradually decreased. By the time the young one is born, the number of potential gametes becomes few lakhs only. After birth this number keeps decreasing further. Most ova at birth are in primary oocyte stage and undergoing first meiotic division. After puberty, the menstrual cycle begins and during each cycle, only one ovum develops further, finally matures and released for fertilization. Mature ovum is also a haploid cell (containing one set of chromosomes) and is capable of undergoing fertilization with sperm. The ovum is enclosed in a special blister like organ on the surface of ovary known as graffian follicle. The process of release of ovum from ovary is called ovulation. At the time of ovulation, the graffian follicle is ruptured and ovum is released into oviduct. Remnant of Graffian follicle develops further and transformed into new temporary structure called corpus luteum (Fig 27c). This corpus luteum survives for 14 days on the ovary and later undergoes regression and finally disappears. Simultaneously new follicles start developing for next menstrual cycle.
  2. Hormone Synthesis: In order to regulate the reproductive system, the various events should be times precisely and regulated in such a manner that chance of fertilization in maximum. This coordination of various events totally depends upon release of hormones from the ovaries.
    Estrogen is release from theca interna layer of graffian follicle and its release coincides with growth of follicle. Estrogen is 18 carbon steroid molecules secreted by theca cells of ovarian follicles. Testosterone is immediate precursor of estrogen. Therefore, female also produce small quantity of testosterone as well. Estrogen hormone dominates during early half of menstrual cycle (5-14 days). Estrogen performs following important functions:
    1. Growth of female reproductive tract
    2. Development of secondary sex characters like fat deposition, broadening of pelvis
    3. Breast development
    Second reproductive hormone from ovaries is progesterone released from corpus luteum. It is a temporary endocrine structure working for 14 days in non pregnancy or for entire gestation length, if pregnancy results. Progesterone is also termed as hormone of pregnancy. Progesterone is 21 carbon steroid molecules. Progesterone is also secreted in pregnant woman from placenta. Progesterone is secreted during later half of menstrual cycle (14-28 days) and during entire pregnancy. Main functions of progesterone are:
  1. Growth of uterine glands for nourishment of embryo.
  2. Relaxation of uterus for providing adequate space to growing fetus.
  3. Breast development and preparation for lactation
  4. This hormone prepares the female genital tract for pregnancy and ensure adequate environment for development of fetus. This hormone along with estrogen is required for growth and development of female reproductive tract, secretion from uterine gland and development of maternal behaviour.

Last modified: Wednesday, 11 April 2012, 7:10 AM