A major goal of all living things is to reproduce and pass genetic material on to their offspring. The reproductive system in humans allows just that with men and women having reproductive structures that accommodate one another to allow for the creation of a new human being. You and everyone you know would not be here without the reproductive system. It is what brought you life and will bring life to others for many generations to come, but how does it all work?
Male Reproductive System
- Testicles: produce sperm cells
- Epididymis: collection duct for mature sperm cells
- Vas Deferens: tube that transports mature sperm to seminal vesicle
- Seminal Vesicle: storage site for sperm until ejaculation
- Prostate Gland: surrounds urethra and secretes a thin, milky fluid (semen) to aid the mobility of sperm
- Bladder: stores fluid (from drinking or digestion) to be excreted as urine
- Urethra: tube that connects to the tip of the penis to excrete urine and semen
- Penis: male reproductive organ; when erect is inserted in the vagina of a female to transfer sperm for start of reproduction
Female Reproductive System
- Ovary: storage site for eggs
- Fimbriae: finger-like projections that catch eggs after ovulation to move them down the fallopian tube
- Fallopian Tubes: tube that moves egg to the ovary; fertilization usually occurs here
- Uterus: receives fertilized eggs and provides an environment for development of the fetus
- Endometrium: lining of the uterus; gets shed off during menstruation (period)
- Cervix: narrow end of vagina that bridges the uterus and vagina
- Vagina: passageway for menstrual flow; site of insertion for penis during sex; birth canal for developed infant
Gametogenesis
Gametogenesis is the formation of gametes, or sex cells, for the purpose of reproduction. Men produce sperm cells (spermatogenesis) and women produce eggs (oogenesis) that fuse together during fertilization. While men actively produce sperm cells after puberty, the ovaries in the female body house all of the eggs (about 500) she will ever have. The process of producing both gametes is a series of divisions that result in cells with one copy of chromosomes (packages of DNA) to be passed on to the baby. At first, both start as cells with 46 chromosomes, having two sets (one from mom and one from dad). Following division, these are split up to leave the single 23 chromosome sex cells. For men, spermatogenesis creates four sperm cells, each with a unique set of the 23 chromosomes. For women, a small polar body is shed that houses the extra chromosomes resulting in a single ovum that prepares to be fertilized. This chain of divisions is displayed below:
Reproduction
During ovulation, an egg (ovum) is released from the ovary and into the infundibulum. Here, the sperm are able to fertilize the egg by fusing together their genetic material. This now creates the 46 chromosome zygote that will begin to divide and form a new human being. Following fertilization, the zygote travels down the fallopian tube and divides along the way. Once it reaches the uterus, it is a small cluster of identical cells. This ball of cells then implants into the lining of the uterus and begins to hollow out and forms a blastocyst. This process takes about five days. From here the cells continue dividing and growing in size and number to form a baby that will be birthed 9 months later. Below is a visual of the implantation process:
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