Human Male Reproductive System


Image Caption : Male Reproductive System: 3D visualization of the male reproductive system reconstructed from scanned human data. Remaining dormant until puberty, the ultimate goal of the male reproductive system is to produce and deliver the male gamete, sperm to the female where fertilization can occur. The male gonads, the testes, serve two functions: to manufacture motile sperm and produce male sex hormones. The accessory ducts serve to aid in the delivery of sperm from its production site to the exterior of the body. These accessory structures include the epididymis, ductus deferens and urethra. Accessory glands, such as the prostate, seminal vesicles, bulbourethral glands serve to produce semen which is made up of proteins which facilitate the motility of sperm.

MALE REPRODUCTIVE SYSTEM

The male reproductive system, like that of the female, consists of those organs whose function is to produce a new individual, i.e., to accomplish reproduction. This system consists of a pair of testes and a network of excretory ducts (epididymis, ductus deferens (vas deferens), and ejaculatory ducts), seminal vesicles, the prostate, the bulbourethral glands, and the penis.

Illustration of the male reproductive system

INTRODUCTION TO THE REPRODUCTIVE SYSTEM

The major function of the reproductive system is to ensure survival of the species. Other systems in the body, such as the endocrine and urinary systems, work continuously to maintain homeostasis for survival of the individual. An individual may live a long, healthy, and happy life without producing offspring, but if the species is to continue, at least some individuals must produce offspring.

Within the context of producing offspring, the reproductive system has four functions:

  • To produce egg and sperm cells
  • To transport and sustain these cells
  • To nurture the developing offspring
  • To produce hormones

These functions are divided between the primary and secondary, or accessory, reproductive organs. The primary reproductive organs, or gonads, consist of the ovaries and testes. These organs are responsible for producing the egg and sperm cells gametes), and hormones. These hormones function in the maturation of the reproductive system, the development of sexual characteristics, and regulation of the normal physiology of the reproductive system. All other organs, ducts, and glands in the reproductive system are considered secondary, or accessory, reproductive organs. These structures transport and sustain the gametes and nurture the developing offspring.

GONADS

The gonads, the primary reproductive organs, are the testes in the male and the ovaries in the female. These organs are responsible for producing the sperm and ova, but they also secrete hormones and are considered to be endocrine glands.

TESTES

Illustration of a testis within the male reproductive system

Male sex hormones, as a group, are called androgens. The principal androgen is testosterone, which is secreted by the testes. A small amount is also produced by the adrenal cortex. Production of testosterone begins during fetal development, continues for a short time after birth, nearly ceases during childhood, and then resumes at puberty. This steroid hormone is responsible for:

  • The growth and development of the male reproductive structures
  • Increased skeletal and muscular growth
  • Enlargement of the larynx accompanied by voice changes
  • Growth and distribution of body hair
  • Increased male sexual drive

Testosterone secretion is regulated by a negative feedback system that involves releasing hormones from the hypothalamus and gonadotropins from the anterior pituitary.

National Cancer Institute / NIH

Male Reproductive System

Unique for its role in human reproduction, a gamete is a specialized sex cell carrying 23 chromosomes-one half the number in body cells. At fertilization, the chromosomes in one male gamete, called a sperm (or spermatozoon), combine with the chromosomes in one female gamete, called an oocyte. The function of the male reproductive system (Figure) is to produce sperm and transfer them to the female reproductive tract. The paired testes are a crucial component in this process, as they produce both sperm and androgens, the hormones that support male reproductive physiology. In humans, the most important male androgen is testosterone. Several accessory organs and ducts aid the process of sperm maturation and transport the sperm and other seminal components to the penis, which delivers sperm to the female reproductive tract. In this section, we examine each of these different structures, and discuss the process of sperm production and transport.

Male Reproductive System

This figure shows the different organs in the male reproductive system. The top panel shows the side view of a man and an uncircumcised and a circumcised penis. The bottom panel shows the lateral view of the male reproductive system and the major parts are labeled.

The structures of the male reproductive system include the testes, the epididymides, the penis, and the ducts and glands that produce and carry semen. Sperm exit the scrotum through the ductus deferens, which is bundled in the spermatic cord. The seminal vesicles and prostate gland add fluids to the sperm to create semen.

Glossary

blood-testis barrier

tight junctions between Sertoli cells that prevent bloodborne pathogens from gaining access to later stages of spermatogenesis and prevent the potential for an autoimmune reaction to haploid sperm

bulbourethral glands

(also, Cowper's glands) glands that secrete a lubricating mucus that cleans and lubricates the urethra prior to and during ejaculation

corpus cavernosum

either of two columns of erectile tissue in the penis that fill with blood during an erection

corpus spongiosum

(plural = corpora cavernosa) column of erectile tissue in the penis that fills with blood during an erection and surrounds the penile urethra on the ventral portion of the penis

ductus deferens

(also, vas deferens) duct that transports sperm from the epididymis through the spermatic cord and into the ejaculatory duct; also referred as the vas deferens

ejaculatory duct

duct that connects the ampulla of the ductus deferens with the duct of the seminal vesicle at the prostatic urethra

epididymis

(plural = epididymides) coiled tubular structure in which sperm start to mature and are stored until ejaculation

gamete

haploid reproductive cell that contributes genetic material to form an offspring

glans penis

bulbous end of the penis that contains a large number of nerve endings

gonadotropin-releasing hormone (GnRH)

hormone released by the hypothalamus that regulates the production of follicle-stimulating hormone and luteinizing hormone from the pituitary gland

gonads

reproductive organs (testes in men and ovaries in women) that produce gametes and reproductive hormones

inguinal canal

opening in abdominal wall that connects the testes to the abdominal cavity

Leydig cells

cells between the seminiferous tubules of the testes that produce testosterone; a type of interstitial cell

penis

male organ of copulation

prepuce

(also, foreskin) flap of skin that forms a collar around, and thus protects and lubricates, the glans penis; also referred as the foreskin

prostate glanddoughnut-shaped gland at the base of the bladder surrounding the urethra and contributing fluid to semen during ejaculation

scrotum

external pouch of skin and muscle that houses the testes

semen

ejaculatory fluid composed of sperm and secretions from the seminal vesicles, prostate, and bulbourethral glands

seminal vesicle

gland that produces seminal fluid, which contributes to semen

seminiferous tubules

tube structures within the testes where spermatogenesis occurs

Sertoli cells

cells that support germ cells through the process of spermatogenesis; a type of sustentacular cell

sperm

(also, spermatozoon) male gamete

spermatic cord

bundle of nerves and blood vessels that supplies the testes; contains ductus deferens

spermatid

immature sperm cells produced by meiosis II of secondary spermatocytes

spermatocyte

cell that results from the division of spermatogonium and undergoes meiosis I and meiosis II to form spermatids

spermatogenesis

formation of new sperm, occurs in the seminiferous tubules of the testes

spermatogonia

(singular = spermatogonium) diploid precursor cells that become sperm

spermiogenesis

transformation of spermatids to spermatozoa during spermatogenesis

testes

(singular = testis) male gonads

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The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body and within the pelvis.

The main male sex organs are the penis and the testicles which produce semen and sperm, which, as part of sexual intercourse, fertilize an ovum in the female's body; the fertilized ovum (zygote) develops into a fetus, which is later born as an infant.

The corresponding system in females is the female reproductive system.



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