Reproductive System

Learning Outcomes

  • Identify the structure and function of the reproductive system

In simple terms, reproduction is the process by which organisms create descendants. This miracle is a characteristic that all living things have in common and sets them apart from nonliving things. But even though the reproductive system is essential to keeping a species alive, it is not essential to keeping an individual alive.

In human reproduction, two kinds of sex cells or gametes are involved. Sperm, the male gamete, and a secondary oocyte (along with first polar body and corona radiata), the female gamete, must meet in the female reproductive system to create a new individual. For reproduction to occur, both the female and male reproductive systems are essential. It is a common misnomer to refer to a woman’s gametic cell as an egg or ovum, but this is impossible. A secondary oocyte must be fertilized by the male gamete before it becomes an “ovum” or “egg.”

While both the female and male reproductive systems are involved with producing, nourishing and transporting either the oocyte or sperm, they are different in shape and structure. The male has reproductive organs, or genitals, that are both inside and outside the pelvis, while the female has reproductive organs entirely within the pelvis.

The Male Reproductive System

The male reproductive system consists of the testes and a series of ducts and glands. Sperm are produced in the testes and are transported through the reproductive ducts. These ducts include the epididymis, vas deferens, ejaculatory duct and urethra. The reproductive glands produce secretions that become part of semen, the fluid that is ejaculated from the urethra. These glands include the seminal vesicles, prostate gland, and bulbourethral glands.

Illustration shows a cross section of the penis and testes. The penis widens at the end, into the glans, which is surrounded by the foreskin. The urethra is an opening that runs through the middle of the penis to the bladder. The tissue surrounding the urethra is the Corpus spongiosum, and above the Corpus spongiosum is the Corpus cavernosum. The testes, located immediately behind the penis, are covered by the scrotum. Seminiferous tubules are located in the testes. The epididymis partly surrounds the sac containing the seminiferous tubules. The Vas deferens is a tube connecting the seminiferous tubules to the ejaculatory duct, which begins in the prostate gland. The prostate gland is located behind and below the bladder. The seminal vesicle, located above the prostate, also connects to the seminal vesicle. The bulbourethral gland connects to the ejaculatory duct where the ejaculatory duct enters the penis.

Figure 1. The reproductive structures of the human male are shown.

Table 1 describes the major components of the male reproductive system.

Table 1. Components of the Male Reproductive System
Structure Location & Description Function
Bulbourethral glands (2) Pea sized organs posterior to the prostate on either side of the urethra. Secretion of gelatinous seminal fluid called pre-ejaculate. This fluid helps to lubricate the urethra for spermatozoa to pass through, and to help flush out any residual urine or foreign matter. (< 1% of semen)
Epididymis Tightly coiled duct lying just outside each testis connecting efferent ducts to vas deferens. Storage and maturation of sperm.
Penis Three columns of erectile tissue: two corpora cavernosa and one corpus spongiosum. Urethra passes through penis. Male reproductive organ and also male organ of urination.
Prostate gland Surrounds the urethra just below the urinary bladder and can be felt during a rectal exam. Stores and secretes a clear, slightly alkaline fluid constituting up to one-third of the volume of semen. Raise vaginal pH.(25-30% of semen)
Seminal vesicles (2) Convoluted structure attached to vas deferens near the base of the urinary bladder. About 65-75% of the seminal fluid in humans originates from the seminal vesicles. Contain proteins, enzymes, fructose, mucus, vitamin C, flavins, phosphorylcholine and prostaglandins. High fructose concentrations provide nutrient energy for the spermatozoa as they travel through the female reproductive system.
Testes Inside scrotum, outside of body. Gonads that produce sperm and male sex hormones.Production of testosterone by cells of Leydig in the testicles.
Urethra Connects bladder to outside body, about 8 inches long. Tubular structure that receives urine from bladder and carries it to outside of the body. Also passage for sperm.
Vas deferens Muscular tubes connecting the left and right epididymis to the ejaculatory ducts to move sperm. Each tube is about 30 cm long. During ejaculation the smooth muscle in the vas deferens wall contracts, propelling sperm forward. Sperm are transferred from the vas deferens into the urethra, collecting fluids from accessory sex glands en route

The Female Reproductive System

Reproduction can be defined as the process by which an organism continues its species. As noted earlier, in the human reproductive process, two kinds of gametes are involved: the male gamete (sperm) and the female gamete (egg or ovum). These two gametes meet within the female’s uterine tubes located one on each side of the upper pelvic cavity, and begin to create a new individual. The female needs a male to fertilize her egg; she then carries offspring through pregnancy and childbirth.

Side and front views of female reproductive organs are shown. The vagina is wide at the bottom, and narrows into the cervix. Above the cervix is the uterus, which is shaped like a triangle pointing down. Fallopian tubes extend from the top sides of the uterus. The Fallopian tubes curve back in toward the uterus, and end in fingerlike appendages called fimbriae. The ovaries are located between the fimbriae and the uterus. The urethra is located in front of the vagina, and the rectum is located behind. The clitoris is a structure located in front of the urethra. The labia minora and labia majora are folds of tissue on either side of the vagina.

Figure 2. The reproductive structures of the human female are shown. (credit a: modification of work by Gray’s Anatomy; credit b: modification of work by CDC)

Female Reproductive System

  • Produces eggs (ova)
  • Secretes sex hormones
  • Receives the male spermatazoa during
  • Protects and nourishes the fertilized egg until it is fully developed
  • Delivers fetus through birth canal
  • Provides nourishment to the baby through milk secreted by mammary glands in the breast

The major components of the female reproductive system are shown in Table 2.

Table 2. Components of the Male Reproductive System
Structure Location & Description Function
Ovaries (2) Ovoid structures on either side of the uterus in the pelvic cavity Primary sex organs of female; contain ovarian follicles that contain the oocytes. Oocytes are released during the ovulation stage of the menstrual cycle.
Fallopian Tubes (2) Extend from lateral ares of uterus to near the ovaries Transport oocyte to uterus after fertilization and are the sites where fertilization by sperm actually occurs
Uterus Pear shaped structure divided into the fundus and the cervix Site of fetal development during gestation
Vagina Located between rectum and urethra; smooth muscle lined with an epithelial mucous membrane Path for menstrual blood and tissue to leave the body, as well as the fetus during childbirth. Produces a variety of secretions for lubrication and receives secretions that facilitate fertilization.
Vulva Externally located: labia majora and minora, mons pubis, clithoris, vestibule, greater and lesser vestibular glands Sexual function: heavily innervated and provide pleasure when properly stimulated.
Perineum Area between vagina and anus Helps form the muscular floor of pelvis; can be torn during vaginal childbirth
Mammary glands Superficial to pectoral muscles Provide nourishment to the baby through milk secretions

Comparing Male and Female Reproductive Systems

Similarities

The reproductive systems of the male and female have some basic similarities and some specialized differences. They are the same in that most of the reproductive organs of both sexes develop from similar embryonic tissue, meaning they are homologous. Both systems have gonads that produce (sperm and egg or ovum) and sex organs. And both systems experience maturation of their reproductive organs, which become functional during puberty as a result of the gonads secreting sex hormones.

 

Table 3.
Indifferent Male Female
Gonad Testis Ovary
Müllerian duct Appendix testis Fallopian tubes
Müllerian duct Prostatic utricle Uterus, proximal vagina
Wolffian duct Rete testis Rete ovarii
Mesonephric tubules Efferent ducts Epoophoron
Wolffian duct Epididymis Gartner’s duct
Wolffian duct Vas deferens
Wolffian duct Seminal vesicle
Wolffian duct Prostate Skene’s glands
Urogenital sinus Bladder, urethra Bladder, urethra, distal vagina
Urogenital sinus Bulbourethral gland Bartholin’s gland
Genital swelling Scrotum Labia majora
Urogenital folds Distal urethra Labia minora
Genital tubercle Penis Clitoris
Prepuce Foreskin Clitoral hood
Bulb of penis Vestibular bulbs
Glans penis Clitoral glans
Crus of penis Clitoral crura

Differences

The differences between the female and male reproductive systems are based on the functions of each individual’s role in the reproduction cycle. A male who is healthy, and sexually mature, continuously produces sperm. The development of women’s “eggs” are arrested during fetal development. This means she is born with a predetermined number of oocytes and cannot produce new ones.

At about 5 months gestation, the ovaries contain approximately six to seven million oogonia, which initiate meiosis. The oogonia produce primary oocytes that are arrested in prophase I of meiosis from the time of birth until puberty. After puberty, during each menstrual cycle, one or several oocytes resume meiosis and undergo their first meiotic division during ovulation. This results in the production of a secondary oocyte and one polar body. The meiotic division is arrested in metaphase II. Fertilization triggers completion of the second meiotic division and the result is one ovum and an additional polar body.

The ovaries of a newborn baby girl contain about one million oocytes. This number declines to 400,000 to 500,000 by the time puberty is reached. On average, 500-1000 oocytes are ovulated during a woman’s reproductive lifetime. When a young woman reaches puberty around age 10 to 13, a promary oocyte is discharged from one of the ovaries every 28 days. This continues until the woman reaches menopause, usually around the age of 50 years. Occytes are present at birth, and age as a woman ages.

Video Review

Watch the first three videos in this playlist for a review of the reproductive system:

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