The Reproductive System
The human reproductive system consists of internal and external organs that help identify one's phenotype or degree of maleness or femaleness. The reproductive system is a complex organ system that begins to develop and differentiate early after conception. There are both physical and physiological differences between male and female genders. Males tend to have thick facial hair while women tend to develop breasts. But they are only subtly different or even the same at times in human development and maturation. For example, in the first several weeks postfertilization, the gonads are not yet sexually determined and can potentially develop as either male or female. There are also aspects of reproductive physiology that are much more complex. Answers to questions such as why women experience menopause midway through life while men are able to produce sperm cells to the end of normal life have evaded scientists since the phenomena were first discovered. While reproduction includes physiological concepts such as fertilization, implantation, placentation, parturition, and lactation, and the advanced student and clinician should be familiar with them, only the dynamic physiology of gametogenesis will be discussed here.
Gametes are germ or reproductive cells. The male gamete is the sperm cell and the female gamete is the egg or ovum. Gametogenesis is the process of differentiation, development, and maturation of the germ cells. The dynamic changes both in structure and function of the developing and differentiating gametes is called spermatogenesis in males and oogenesis in females. The mature end products, in males a spermatozoan and in females a graafian follicle, bear little resemblance to their primitive progenitor cells called spermatogonia in males and oogonia in females. Gametogenesis can be divided into the study of male gametes (spermatogenesis) and female gametes (oogenesis).