The Reproductive System

Each testicle (or testis) produces sperm (analogous to the female ova), which are passed into a series of coiled tubules called the epididymis. The epididymis stores and nurtures sperm until they are passed into the vas deferens, a tubule that is about 30 centimeters long, extending from the testicle into the pelvis and ending at the ejaculatory duct. The epididymis and vas deferens are supported by several accessory glands (the seminal vesicles, the prostate gland, and the Cowper glands) that produce fluid components of semen and support the sperm cells. During male orgasm, semen passes through the ejaculatory duct into the urethra and is ejaculated from the penis through the urethral opening.

Female Reproductive System

Like all biological systems, the female reproductive system is comprised of several organs. These organs are located within the pelvis or external to the body.

The main female reproductive organs are the uterus (the “womb”) and the ovaries, which are located in the pelvis. The ovaries (analogous to the male testes) produce several important hormones and the ova (analogous to the male sperm). After ovulation, the ovum is transported from the ovary to the uterus though the Fallopian tube. If sperm are present in the Fallopian tube, fertilization may occur. A fertilized zygote embeds in the endometrium of the uterus for gestation; an unfertilized ovum passes out of the body during subsequent menstruation.

The uterus has a lower opening called the cervix, which connects the uterus to the vagina. The female reproductive system has several organs that are external to the body, collectively known as genitals or, specifically, the vulva, including the labia (majora and minora), clitoris, and vaginal opening. When a female is sexually aroused, these external organs become suffused with blood, becoming larger and more erect, and the vagina becomes lubricated.

The uterus performs numerous critical functions during reproduction. It provides mechanical protection, nutritional support, and waste removal for the developing embryo (though a complex interfacing with the embryo’s placenta). In addition, it is a powerful, muscular organ that is capable of contractions that push the fetus through the vagina at the time of birth.

Reproduction

Human reproduce sexually, with a male partner (the “father”) providing sperm and a female partner (the “mother”) providing an ovum and all subsequent protection and nourishment until the fetus is delivered.

Post-natal feeding is provided by the female’s breasts. Human intercourse consists of the male introducing sperm into the female’s reproductive system. Sperm may then pass through the female’s reproductive system to the Fallopian tubes where one sperm fertilizes an ovum, creating a zygote. The zygote passes out of the Fallopian tube and implants into the uterine wall to begin gestation. Over nine months, the zygote develops and grows into an embryo and then a fetus.

At the abdomen, the fetus is connected to the umbilical cord, which connects to the placenta. The umbilical cord and placenta are formed from fetal tissue. The placenta shares a complex interface with the endometrial lining of the uterus. The endometrium and uterus are maternal tissue. Hormones, food, and fetal waste all pass through the placental/uterine interface and along the umbilical cord. As the fetus grows, the placenta also grows. The fetus is encapsulated in a tough container of fetal tissue, filled with fluid, called the amniotic sac.

During the early stages of delivery, the amniotic sac ruptures and the fluid passes through the mother’s vagina (this is colloquially known as “water breaking”). Also, the cervix softens and dilates to accommodate the fetus. Powerful muscular contractions of the uterus force the fetus through the cervix and out the vagina, normally with the head emerging first. After the fetus is delivered, hormonal signals in the mother’s body cause the endometrial lining to quickly disconnect from the placenta, and the placenta is delivered through the vagina (the “afterbirth”).

In some cases, surgical removal of the fetus may be desirable or necessary. This process delivers a live baby and colloquially is known as Caesarean section (or C-section).

Development

Human newborn infants are unable to care for themselves and survive only with a large amount of parental care extending over at least the first several years of life. At birth, humans have all of the basic structures of the adult reproductive system, though some are undeveloped. At about 10–11 years old in females and about 11–12 years old in males, a child enters puberty, during which hormonal changes cause the reproductive system to develop fully. Puberty lasts for about 5–7 years.

Menstruation is a cyclical process occurring in the female body, especially the reproductive system, from about the end of puberty until menopause. During each period of menstruation, fluctuating hormone levels cause the uterus to change in anticipation of receiving a zygote. At the midpoint of the menstrual cycle, an ovum is released from an ovary and travels down the Fallopian tube. If the ovum is not fertilized, it passes out of the body along with the endometrium (lining of the uterus), causing menstrual bleeding. If the ovum is fertilized, the zygote implants in the endometrium and pregnancy follows.

There are significant differences between male and female bodies. The primary differences can be noted in the reproductive organs, but numerous other differences are the result of secondary sex characteristics. Male secondary sex characteristics include facial hair and a generally larger body. Female secondary sex characteristics include enlargement of the breasts and widening of the hips.

Let’s Review

• The reproductive system enables sexual reproduction in humans.
• Components of the reproductive system are often known by multiple names, some of which are common or “slang” terms; the correct biological or medical terms are always preferred.
• The male reproductive system provides the sperm, the carrier of the genetic contribution from the father.
• The female reproductive system provides the ovum, or egg cell, which contains the genetic contribution from the mother. Additionally, the female reproductive system supports fertilization; provides the mechanical protection and nurturing environment needed for embryogenesis and gestation; and performs the actions necessary for the birth of the infant.
• The male testicles are analogous to the female ovaries. There are other similarities in the male and female reproductive systems.
• Sexual maturity occurs during puberty. Humans are capable of reproduction for several decades.

Reproductive System Flashcards