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Fertility Education

No matter where you are in your fertility journey, for both males or females, having a baseline understanding of the science of fertility is important. This page will give you a general idea of some of the processes and reproductive organs that our team at Arizona Center for Reproductive Endocrinology and Infertility may refer to as we consult with you along your time with us.

Learn more about:

Female Reproductive System

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Menstrual Cycle Phases

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How fertilization occurs

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Male Reproductive System

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Sperm + egg fertilization factors

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The female reproductive system:

The female reproductive system is mainly internal. The vagina is the passage that leads from the outside of the body to the cervix, which is the opening to the uterus. The uterus is a muscular organ about the size and shape of a pear, which is lined with a rich and nourishing mucous membrane called the endometrium. The uterus is where a fertilized egg attaches itself and develops into a baby.

The ovaries are the two small structures that store the woman’s eggs. In addition to developing a mature egg during each menstrual cycle, the ovaries produce the female hormones estrogen and progesterone. Each month, only a single egg (ovum) matures inside a follicle (capsule) within an ovary. At mid cycle, the egg is released from the follicle in a process called ovulation. The egg then enters one of the fallopian tubes, traveling toward the uterus. At the end of the fallopian tube, near the uterus, the egg is ready for fertilization.

Glossary:

  • Fallopian Tube: pair of tubes along which eggs travel from the ovaries to the uterus.
  • Ovary: where ova or eggs are produced
  • Cervix: muscular, tunnel-like and connects uterus to vagina
  • Uterus: where fertilized egg implants + develops
  • Vagina: passage leading from external genitals to cervix (opening to uterus).

The menstrual cycle:

The menstrual cycle is a 4-phase process that refers to the time between each monthly shedding of the endometrial lining. Each normal cycle includes the maturation and release of an egg followed by the preparation of the uterine lining to receive and nurture an embryo, the early fetal growth up through pregnancy. If a fertilized egg is not present, the uterus will shed the lining, beginning the woman’s period and the next menstrual cycle. The typical cycle takes approximately 28 to 32 days and is divided into three distinct phases.

THE LUTEAL PHASE

The luteal phase begins after ovulation occurs. During the luteal phase, the follicle that released the egg becomes a functioning gland called the corpus luteum. The corpus luteum produces progesterone, which prepares the uterus with the rich lining needed for implantation.

FERTILIZATION

Fertilization requires that intercourse take place during midcycle. Sperm travel up through the female reproductive tract to meet the egg. For fertilization to occur, the ovum, or egg, must meet with the sperm at the end of the fallopian tube. The fertilized egg (now called the embryo) moves into the uterus. Once inside the uterus, the embryo implants into the lush lining on or about the 20th day of the cycle. If fertilization occurs, the corpus luteum detects the pregnancy and continues to produce progesterone, thus preserving the uterine lining and pregnancy. If fertilization does not occur, the corpus luteum will cease to function on about Day 26. The uterine lining will then break down and be shed several days later, starting the next menstrual period.

Glossary:

  • Sperm Nucleus: Central part of a sperm cell that contains genetic material, contributing to the formation of the embryo upon fertilization.
  • Vitelline Membrane: Protective layer surrounding the egg cell (ovum), aiding in regulating interactions between the egg and the external environment.
  • Zona Pellucida: A glycoprotein-rich layer that surrounds the mammalian egg cell, playing a crucial role in fertilization by permitting only specific sperm to penetrate and bind to the egg.
  • Acrosome: A cap-like structure at the tip of a sperm cell’s head that contains enzymes, enabling the sperm to penetrate the egg’s protective layers during fertilization.
  • Sperm: Microscopic male reproductive cells produced in the testes that carry genetic information and are crucial for fertilizing an egg.
  • Cytoplasm of Ovum: Fluid-like substance within an egg cell that contains organelles and nutrients necessary for supporting early development after fertilization.
  • Egg Nucleus: Central part of an egg cell that houses genetic material and combines with the sperm nucleus during fertilization.
  • First Polar Body: Small, non-functional cell produced during oogenesis that contains half the genetic material of the egg and is expelled during fertilization.

The male reproductive system

The male reproductive system is both internal and external. The testes are located within the scrotal sac, the fleshy pouch of skin located below the man’s penis. The testes produce sperm and testosterone, the primary male hormone that helps maintain the male sexual characteristics. As sperm are produced, they pass from the testes through the coiled channels of the epidiymis, which stores and nourishes them as they mature. The mature sperm then move into the vas deferens, the tubal structure that transports sperm from the epididymis to the seminal vesicles. The seminal vesicles and the prostate gland both empty fluids combine with the sperm to produce semen, which is ejaculated during intercourse.The pituitary hormones, FSH and LH, are responsible for maintaining the sperm production process. These are the same hormones necessary for regulating the female’s reproductive functions. FSH is responsible for stimulating sperm production in the testicles, and LH stimulates the production of testosterone. Immature sperm cells develop through several stages to become mature sperm cells. As the sperm pass through the epidiymis, they gain motility (movement). This process takes about 18 to 24 hours, after which they are stored in the vas deferens awaiting ejaculation. The entire process of sperm maturation takes about 72 days. However, this is an ongoing process and millions of sperm are being manufactured all the time.

Glossary:

  • Vas Deferens: The vas deferens is a duct in the male reproductive system that carries sperm from the epididymis to the ejaculatory duct, playing a vital role in transporting sperm during ejaculation.
  • Pubic Bone: The pubic bone is a sturdy, front part of the pelvis that protects internal reproductive and urinary organs, and serves as an attachment site for muscles.
  • Penis: The penis is the male external genital organ, involved in both the elimination of urine and the delivery of sperm for reproduction.
  • Urethra: The urethra is a tube connecting the urinary bladder to the external body, through which both urine and semen (during ejaculation) pass.
  • Scrotum: The scrotum is a pouch-like structure located beneath the penis that contains the testicles and helps regulate their temperature for proper sperm production.
  • Testicle: The testicle (or testis) is a male reproductive gland responsible for producing sperm and hormones, primarily testosterone.
  • Epididymis: The epididymis is a coiled tube attached to each testicle where sperm mature and gain motility before being transported to the vas deferens.
  • Prostate: The prostate is a gland located beneath the bladder that produces seminal fluid, which nourishes and transports sperm during ejaculation.
  • Rectum: The rectum is the lower part of the large intestine, serving as the terminal segment of the digestive system before the anus.
  • Ejaculatory Duct: The ejaculatory duct is a tube formed by the convergence of the vas deferens and the seminal vesicles, allowing the passage of sperm and seminal fluid to the urethra during ejaculation.
  • Seminal Vesicle: Seminal vesicles are glands that secrete a significant portion of the fluid that becomes semen, providing nutrients and enhancing the mobility of sperm.
  • Bladder: The bladder is a muscular organ that stores urine before it’s eliminated from the body through the urethra.

Several factors determine whether a man’s sperm can fertilize an egg:

  • Volume of semen
  • Sperm count or density
  • Sperm motility
  • Forward progression
  • Sperm shape
Although sperm count is critical, sperm motility and forward progression appears to be the more important factors in determining the fertilizing capability of sperm. Despite a low sperm count, many men with high-quality (viable and highly motile) sperm may still be fertile. The Importance of Timing For most couples, the probability of pregnancy occurring in any one month is only about 20%. There are several days each month during which conception is possible. The best time for intercourse is midcycle, during ovulation. At this time, the egg is positioned in the fallopian tube and remains there for about 24-48 hours, awaiting fertilization by the man’s sperm. Sperm can live 48 to 72 hours within the female reproductive tract. However, even in a perfectly timed cycle, pregnancy does not always occur. There may be several reasons for this, including the fact that some eggs don’t fertilize and some of the fertilized eggs don’t develop well in the early stages.
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