Human Reproduction: Life Stages & Systems

Human Reproduction & Sexuality

Human reproduction is sexual and has two key characteristics:

• The new individual is formed from a single cell called a zygote.
• Zygotes result from the union of two gametes (fertilization).

Humans have two types of gametes: sperm (men) and ova (women).

Changes During Reproductive Life

During the reproductive life of a human being, there are three main stages:

• Puberty

  Puberty begins in men with the first ejaculation (spermarche) and in women with the first menstruation (menarche). This is due to the increased secretion of pituitary hormones: Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH), which stimulate gamete production.

  Puberty typically begins when girls are 10-13 years old and boys 12-14. It lasts 3-4 years and produces significant anatomical, physiological, and psychological changes.

• Adolescence

  In this stage, individuals begin to develop their sexuality and become capable of reproduction.

  In women, these changes are a consequence of releasing ova and sexual hormones (estrogen and progesterone) from the ovaries. In men, they are a consequence of releasing sperm and sexual hormones (testosterone) from the testicles.

  The main physical changes include an increase in the size of sexual organs, the growth of body hair (men also develop facial hair), breast development and widening of the pelvis in women, and narrowing of the pelvis and broadening of the shoulders in men. The larynx and vocal cords of men also thicken.

• The End of Reproductive Life

  Ovaries typically cease functioning when women reach approximately 50 years of age; the activity of men's testicles decreases from that age onwards. This leads to physical and psychological changes known as menopause (in women) and andropause (in men).

The Human Reproductive System

Male and female reproductive systems are formed by gonads, ducts, and glands that participate in the sexual act as well as in the development of the embryo.

The Male Reproductive System

The male reproductive system is formed by the:

• Testicles
• Penis
• Reproductive tract
• Male accessory glands

Most of these parts are located outside the body.

The Ovarian Cycle

Oogenesis occurs in women from puberty onwards and takes place approximately every 28 days. The cycle consists of three main phases:

1. Follicular Phase

   This phase lasts approximately 14 days and occurs due to the Follicle-Stimulating Hormone (FSH) produced by the pituitary gland. FSH stimulates the development of one or several follicles.

2. Ovulation

   This consists of the release of an ovum from the ovary as a consequence of the production of Luteinizing Hormone (LH) by the pituitary gland.

3. Secretory Phase

   Once the ovum is released, the corresponding area transforms into a mass of cells that produces and secretes the hormone progesterone. After approximately 10 days, this structure, known as the corpus luteum, degenerates and stops secreting hormones.