GYN 8

• The first menstruation (menarche) occurs between 11 and 15 years with a mean of 13 years
• Menarche is more closely related to bone age than to chronological age
• The age of menarche is gradually declining with improvement of nutrition and environmental condition
• Once the menstruation starts, it continues cyclically at intervals of 21–35 days with a mean of 28 days
• Menstruation is kept in abeyance due to pregnancy and lactation
• Menstruation ceases between the ages 45–50 when menopause sets in
• The duration of menstruation is about 4–5 days
• The amount of blood loss is estimated to be 20–80 mL with an average of 35 mL
• Nearly 70% of total menstrual blood loss occurs in the first 2 days
• The menstrual discharge consists mainly of dark altered blood, mucus, vaginal epithelial cells, fragments of endometrium, prostaglandins, enzymes and bacteria
• Follicular Growth and Atresia

  1. Germ cells

  2. Primordial follicle

  3. Cyclic maturation of the follicle (ovarian cycle)

  4. Ovulation

  5. Corpus luteum

  6. Follicular atresia

  
• Germ cells

  Cells that migrate from the endoderm of the yolk sac in the region of hindgut, into the genital ridge (between 5 and 6 weeks of gestation), passing through the dorsal mesentery of the hindgut

  
• A peptide called telopheron directs the anatomic migration of germ cells
• The migration of germ cells is probably through amoeboid activity or by chemotactic mechanism between 4 and 6 weeks gestation
• In the gonadal ridge, the oogonia are surrounded by clumps of epithelial cells
• The germ cells undergo rapid mitotic division and by 20 weeks, the number reaches about 7 million
• While majority of the oogonia continue to divide until 7th month of gestation, some enter into the prophase of first meiotic division and are called primary oocytes

  
• Primary oocytes are surrounded by flat cells from the stroma (pregranulosa cells) and are called primordial follicles
• Primary oocytes continue to grow through various stages of prophase (leptotene, zygotene, pachytene and diplotene) and ultimately reach to the stage of diplotene or else become atretic

  
• Primary oocytes are then arrested in the diplotene stage of prophase of first meiotic division, until ovulation

  
• At 20 weeks' of intra uterine life, the total number of oocytes is about 6–7 million
• At birth, the total number of primordial follicles is estimated to be about 2 million
• The primary oocytes do not finish the first meiotic division until puberty is reached
• At puberty, some 4,00,000 primary oocytes are left behind, the rest become atretic
• During the entire reproductive period, some 400 are likely to ovulate
• The degeneration of sex cells starts in the intrauterine life and continues throughout childhood and the childbearing period
• No more follicles with ova can be detected in menopausal women
• Primordial follicle


  Consists of an oocyte, surrounded by a single layer of flattened granulosa cells. Measures about 0.03–0.05 mm.

  
• Throughout childhood, the primordial follicles grow very slowly. This growth is not dependent on gonadotropin.

  
• Oocyte


  Measures about 130 microns and the nucleus measures 20–25 microns just prior to ovulation. It is surrounded by radially arranged granulosa cells called corona radiata and an outer envelope called zona pellucida, a glycoprotein layer. The cytoplasm contains nutritive yolk granules and is limited by a vitelline membrane.

  
• Ovarian cycle


  The development and maturation of a follicle, ovulation and formation of corpus luteum and its degeneration, occurring within 4 weeks.

  
• Ovarian cycle


  1. Recruitment of cohort of follicles

  2. Selection of dominant follicle and its maturation

  3. Ovulation

  4. Corpus luteum formation

  5. Demise of the corpus luteum

  
• About 20 antral follicles (about 5–10 per ovary) proceed to develop in each cycle

  
• The initial recruitment and growth of primordial follicles are not under the control of any hormone. After a certain stage (2–5 mm in size) the growth and differentiation of primordial follicles are under the control of follicle-stimulating hormone (FSH).

  
• Unless the follicles are rescued by FSH at this stage, they undergo atresia.
• The predominant change is in the oocyte which is enlarged out of proportion to the size of the follicle. The oocyte is now surrounded by an acellular barrier of glycoprotein produced by the follicular cells and is called zona pellucida.

  
• The flattened outer single layer pregranulosa cells become cuboidal and multilayered—now called granulosa cells.

  
• There is appearance of channels (gap junctions) between the granulosa cells and the oocyte. Through these gap junctions nutrition to the oocyte is maintained.
• There is noticeable beginning of differentiation of the theca interna layer of ovarian stroma surrounding the follicle.

  
• The granulosa cells now acquire FSH receptors.