Biology

Male Reproductive System

Big Picture

The male reproductive system, consisting of the penis, testes, and epididymes, is necessary for reproduction. The system forms before a child is born, but until hormones called testosterone are released during puberty (which occurs when a male is 12-18 years old), the male reproductive system remains immature. The secretion of testosterone after puberty allows males to produce sperm via spermatogenesis. Matured sperms are then released from the body during ejaculation.

Key Terms

Reproductive System: The system of organs that produces gametes and secretes sex hormones.

Penis: Male reproductive organ containing the urethra, through which sperm and urine pass out of the body.

Epididymis (plural, epididymes): One of two male reproductive organs where sperm mature and are stored until they leave the body.

Testis (plural, testes): One of two male reproductive organs that produces sperm and secretes testosterone.

Sperm: Male gamete (reproductive cell produced during meiosis with a haploid number of chromosomes).

Testosterone: Male sex hormone that promotes protein synthesis and growth, causing the most physical change during puberty.

Sex Hormone: Chemical messenger that controls sexual development and reproduction.

Semen: Fluid containing sperm and gland secretions that nourish sperm and carry them through the urethra and out of the body.

Spermatogenesis: Process of producing sperm in the testes.

Ejaculation: Muscle contractions that propel sperm from the epididymes and out through the urethra in males.

Puberty: Period during which humans become sexually mature.

Luteinizing Hormone (LH): Pituitary gland hormone that stimulates the testes to secrete testosterone and the ovaries to secrete estrogen.

Adolescent Growth Spurt: Period of rapid growth that occurs during puberty.

Male Reproductive Structures

Main structures of the male reproductive system:

  • Penis: external genital organ with a long shaft and enlarged tip
  • The urethra passes through the penis; sperm and urine exit the body through the urethra
  • Testes: located beneath the penis; produce sperm, excrete testosterone; covered by the scrotum (sac of skin)
  • Epididymis: coiled tube lying atop the testis that stores sperm

Ducts and Glands

  • Ducts (vas deferens and ejaculatory ducts) trans-port sperm
  • Glands (seminal vesical, prostate gland) secrete substances that become part of semen
  • Epididymis: coiled tube lying atop the testis that stores sperm
Ducts and Glands‍

Biology

Male Reproductive System cont.

Production & Delivery of Sperm

Spermatogenesis:

  • Sperm are made inside seminiferous tubules of the testes and become mature in the epididymis
  • Tubule is lined with spermatogonia (diploid cells that produce sperm)
  • A diploid cell contains the usual number of chromosomes
  • Spermatogonia go through mitosis, produce diploid primary spermatocytes
  • Primary spermatocytes go through first part of meiosis, produce haploid secondary spermatocytes
  • Haploid cells contain half the usual number of chromosomes.
  • Secondary spermatocytes finish meiosis, form spermatids
  • Spermatids move to epididymis, mature into sperm: grow a tail, lose extra cytoplasm in the head
  • The tail allows the sperm to propel itself forward

Sperm are released during ejaculation.

  • The sperm are forced through the ducts and through the urethra
  • Mix with fluids from glands to form semen
  • Hundreds of millions of sperm are released with each ejaculation

Sexual Development

Development Before Birth

During the early stages after fertilization, females and males are basically the same. The differences lie in the Y chromosome in males. During the 2nd month of fertilization, the Y chromosome causes the secretion of testosterone. Without testosterone, all reproductive organs will develop into female parts.

Puberty and its Changes

Although boys have their reproductive organs when they are born, these organs don’t mature until puberty. In America, puberty on average starts at age 12 and ends at age 18. Puberty begins when the hypothalamus in the brain signals the pituitary gland to secrete hormones, namely luteinizing hormone (LH), that target the testes. LH stimulates the testes to secrete testosterone, which in turn promotes protein synthesis and growth. Some of the physical growth that occurs include the growth of pubic hair and the enlargement of the penis and testes.

Adolescent Growth

During an adolescent growth spurt, males go through rapid growth. Controlled by testosterone, growth can reach 10 cm a year. Development of muscles occurs near the end of the growth spurt in height.

Notes