Fertility Education

Sperm & Egg

Sperm

The male reproductive system consists of three main components:

  • Testicles
  • Epididymis
  • Vas deferens
1. Testicles(testes)
  • The testicles are paired organs, approximately 1.5 - 2 inches long, located within the scrotum (a multi-layered muscular structure that protects the testes and helps with temperature regulation). The testicles have two very important functions that are essential for normal male fertility: the first is the production of testosterone and the second is the production of sperm. Sperm only start their development in the testes. From there, they move on to the epididymis where they mature and are stored.
2. Epididymis
  • The epididymis is the long, narrow tube, which is coiled and contained beneath a fibrous sheath. Uncoiled, the epididymis would be approximatey nineteen feet in length. The epididymis sits on the back of the testis, and it is divided into head, body and tail regions. Here sperm undergo their final development and maturation, and are stored until they are ejaculated. From the epididymis, sperm proceed into the vas deferens, also known as the spermatic cord.
3. Vas Deferens
  • The vas deferens is also a long, tube-like structure that connects the epididymis (where the sperm is stored) to the urethra (the tube that expels sperm). Although the urethra also expels urine, there is a valve that controls the flow of sperm versus urine. During ejaculation, the sperm flows out of the testicles, through the vas deferens and into the urethra. Seminal fluid is added by the prostate and other glands as the sperm flow outside the body through the penis.

Normal Male Reproduction
The production of sperm is a very complicated process that begins at puberty and lasts, in healthy males, until death. The production of sperm begins in the testicles and is controlled by several hormones. These hormones are regulated by the hypothalamus and the pituitary gland located in the brain.

Sperm and egg in reproduction

The hypothalamus regulates the hormonal activity of the pituitary gland by secreting gonadotropin-releasing hormone (GnRH). This hormone controls the production of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), from the pituitary. LH triggers the production of testosterone (a hormone needed for sperm production). FSH also triggers hormones that help with sperm production.

From beginning to end, sperm production takes about 72 days. Sperm spend their first 50 days in the testicles and the last 22 to 24 days in the epididymis. It is in the epididymis that sperm mature and gain motility (the ability to swim). During sexual activity, motile sperm are ejaculated into the female reproductive tract and begin their journey through the cervix and uterus to the fallopian tubes, the site of fertilization. There are many pockets (crypts), folds or 'wrong turns' along the way that can prevent many of the sperm from reaching their final destination. This is why so many sperm are needed for the fertilization process.

Egg

By understanding the reproductive process, you can understand that there are numerous places where the system may not work properly and thus result in infertility.

The female reproductive system consists of three main components:

  • Ovaries
  • Fallopian Tubes
  • Uterus
1.Ovaries
  • The ovaries are oblong (1-2 inches) organs that are just below the fallopian tubes on each side of the uterus. The ovaries contain about a half a million immature eggs. All the eggs that a woman will ever have are produced while she is still a fetus. Only a fraction, about 300-400 eggs, of a woman's supply will ever develop into ovulated eggs during her lifetime. After puberty, many eggs will start the developmental process each month however only one is usually released or ovulated each month. After the egg is released from the ovary, it is picked up by the fallopian tube.
2. Fallopian Tubes (oviducts)
  • The fallopian tube is one of the most complex organs in the body. This is where fertilization takes place. The tubes have a fan-like ends called fimbria that can sweep across the ovary and pick up the ovulated egg. Nearly one-half inch at its open end close to the ovary, the tube narrows to the size of a pencil tip near the uterus. The end closest to the ovary contracts to push the egg down to the site of fertilization while the end closest to the uterus contracts up to aid in getting the sperm to the site of fertilization. The fallopian tubes sustain the female's egg and male's sperm throughout the fertilization process. It may take a few days for the egg and the subsequent fertilized embryo to travel the length of the fallopian tube.

Fallopian tubes are responsible for:

  • Picking up a newly released egg
  • Providing nutrients and movement for the egg
  • Sustaining an environment for fertilization
  • Moving a fertilized egg into the uterus
3.Uterus
  • The uterus is a pear-shaped organ located in the low center of a woman's pelvis. The uterine lining, known as the endometrium, builds up during the first half, proliferative phase, of the menstrual cycle in anticipation of receiving an embryo from the fallopian tube. It protects, develops and nourishes the fetus until birth. The uterus is also referred to as the womb. If a woman is not pregnant, the uterine lining sheds in the menstrual cycle (i.e. menses).
  • The cervix is the connection between the vagina and the uterus. For intrauterine insemination or for embryo transfer, a catheter is inserted through the vagina and cervical canal to reach the uterus. The cervix produces mucous secretions that change through the reproductive cycle. Around the time of ovulation, the cervical mucous is thin and watery to aid in the passage of sperm to the uterus. After ovulation and/or during pregnancy, the mucous is thick to provide a protective barrier to the uterus from infections.

Normal Female Reproduction
Beginning the first day of menstruation, the body starts to make and release increasing amounts of follicle-stimulating hormone (FSH). This hormone, produced by the pituitary gland at the base of the brain, causes the follicles to grow and produce estrogen. The egg that is developing inside the follicle also begins to mature. During the average cycle, around day 14, the pituitary gland releases a burst of another hormone called luteinizing hormone (LH); this is referred to as the LH surge. LH stimulates the final maturation of the egg and starts the ovulation process - resulting in the release of a mature egg from the follicle. As the egg travels through the fallopian tube, the ovulated follicle forms a cyst known as the corpus luteum, which produces levels of another female hormone, progesterone. Progesterone aids in the preparation of the uterine lining for the soon-to-be fertilized embryo.

If there are sperm present in the fallopian tube, the egg may be fertilized and the resulting embryo will pass through the fallopian tube and enter the uterus (a 5-day journey), where it will implant and grow into a baby. If the egg is not fertilized, it will travel to the uterus. Approximately two weeks after ovulation the uterus sends a signal to the ovary to decrease progesterone production since no pregnancy occurred and menstruation, or the shedding of the lining of the uterus, will follow. The cycle will begin anew the next month.

Last updated: July 22, 2008
Author: Dr. Arlene J. Morales

 

 

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