Differentiation and Function of the Female Reproductive System

Reproduction in mammals is a complex process in which numerous haploid gametes from a male are deposited into the reproductive tract of a female. The male gametes, or spermatozoa, are propelled to the fallopian tubes of the female reproductive tract, where they encounter a female gamete, or oocyte. The oocytes start out as primordial germ cells that migrate to the ovary during fetal development to become mitotically active oogonia. Subsequently, oogonia become oocytes when they begin meiosis and are then surrounded by granulosa cells to form primordial follicles. At puberty, groups of follicles grow and eventually one oocyte is selected for ovulation. A single spermatozoon fertilizes the oocyte and initiates a process of combination of paternal and maternal chromosomes, sequential expression of embryonic genes, implantation of the embryo in the wall of uterus, and development of a fetus. Changes in maternal physiology during pregnancy facilitate fetal growth and development. When the fetus matures to a stage at which it can survive outside of the uterus, chemical signals from the fetus and mother induce muscular contractions of the uterus to expel the fetus in the process of parturition. Postpartum maternal physiology gradually returns to the antepartum state and the maternal breasts provide milk to nourish the newborn. The female reproductive period commences at puberty and subsides at menopause.