To understand the biology of reproduction, we must
first meet the cast of characters involved in this fascinating
process. In Chapters 2 and 4, we will study the anatomical
components of the female and male reproductive systems.
However, you will discover that, to function properly,
these systems require chemical instructions. In fact, nearly
every aspect of reproductive biology is regulated by internal
molecular messengers called hormones. Reproductive
hormones signal the reproductive structures to grow and
mature. For example, as a boy approaches puberty, circulating
levels of hormones called androgens rise and cause
his reproductive tract to mature. In addition, these hormones
induce muscle growth, cause changes in the vocal
cords that lower the young man’s voice, and initiate adult
patterns of body hair growth. Hormones also regulate the
timing of reproductive events. In women, the coordinated
release of several female hormones orchestrates ovulation,
the release of an egg from the ovary, approximately every
28 days. This chapter will introduce you to the endocrine
system, focusing on how the brain and pituitary gland
regulate reproductive hormones. Your efforts in studying
this material will be repaid as you read further in the text,
as an understanding of this topic is essential for you to
grasp the information in subsequent chapters.