Module 3 Lesson 4 - 5
Lesson 4 — Sex Development and Male Hormones
Lesson Summary
Sexual reproduction is necessary to provide variation in a species. The formation of male and female sex in embryos is a complex process that is influenced by chromosome structure and sexual hormones secreted. Because all eggs carry the X chromosome and sperm carry either X or Y chromosomes, the male parent determines sex. Typically, for an organism to be a genetic male, it must carry the XY sex chromosomes; for an organism to become a genetic female, it must carry the XX sex chromosomes. After the chromosomal structure of the individual is determined, various hormones continue the sexual development of the embryo.
For a male embryo to develop the SRY region with the TDF gene, a chain of events begins that leads to the production of testosterone and the eventual outcome of a male fetus. Although the process is not fully understood, the chain of events that leads
to the development of a female embryo occurs due to lack of testosterone and other male hormones. Ovaries and the hormones they produce lead to the development of a female fetus.
Sex determination begins at conception but continues through to
puberty when the final stages of sex determination are completed.
Although sex is first controlled by the chromosome arrangement received
from the parents, hormones lead to sexual development
and gamete production.
Male hormone production begins in an embryo in the uterus. The process of sexual maturation occurs during puberty, which begins with increased production of GnRH from the hypothalamus. GnRH causes the anterior pituitary to produce both FSH and LH. The production of FSH causes the testes to start producing sperm and the hormone inhibin, which feeds back negatively to the pituitary to control further production of FSH.
Chemical hormone control of the mature male reproductive system causes a peak in testosterone levels during three major times in a male's life: in utero, at birth, and during puberty. After puberty, testosterone levels stay at a steady rate for most of the remainder of a man's life. Levels of testosterone can begin to drop at about age 40, a condition sometimes referred to as andropause in men. Although a male continues to produce testosterone throughout his life, sperm count reduces as he ages.
Understanding the scientific effect of testosterone on the body has led to the technological production of synthetic anabolic steroids. Although steroids can sometimes be used to treat disorders such as naturally low testosterone levels (called hypogonadism),
anabolic steroids affect society in much greater ways through their misuse. The desire to look or perform better may lead some individuals to misuse anabolic steroids even when they are informed of the risk factors involved.