After reading these two chapters I think it is a wonder that the human race endures to this day. Both the egg and the sperm follow very complex paths to the site of fertilization; paths riddled with difficulty and improvisation. In fact, I would liken the path of the egg and sperm with two secret agents; undercover as it were. Both the egg and sperm must be developed and trained in the art of fertilization. They must traverse great distances and overcome great odds in order to accomplish their mission, but in the end, fate brings them together.
I was amazed to learn that sex cell development for both males and females starts with hormone glands. The development of sperm starts in the hypothalamus with a hormone called LH-RH (Finchner-Rathus, Nevid, Rathus, 2005). The releasing of this hormone into the bloodstream signals the pituitary gland to release LH and the testes to release testosterone. This causes the hypothalamus to secrete FSH-RH which makes the pituitary gland then release FSH. This whole process ends with the production of sperm in the testes. Once the testes have been signaled to produce sperm the process of spermatogenesis begins. In the beginning stages of sperm production sperm cells are called spermatocytes and contain 46 chromosomes, including both the X and Y sex chromosomes. The first step is for the spermatocytes to divide into two spermatids, both with 23 chromosomes. The fully developed spermatocytes are called spermatozoa which contains a nucleus including the chromosomes. At this point, the sperm waits until sexual arousal has been accomplished in the male subject. Then the sperm collects at the base of the penis with other fluids which constitute the semen. At the point of sexual climax, the sperm is released into the female vagina. From there it travels to the uterus through the cervical canal. The male sex cell utilizes a tale that it lashes back and forth to propel itself through the vaginal canal, into the uterus, and finally to the egg in the fallopian tubes. The sperm usually joins the egg in the fallopian tubes and fertilization takes place and reproduction has occurred.
As with male sperm production, the production of the female eggs is triggered by hormone glands. After menstruation has occurred estrogen and progesterone levels are relatively low. The hypothalamus senses this depletion and secretes a hormone called Gn-RH, which causes the pituitary gland to release FSH. The hormone FSH then stimulates the ovaries to mature between 10 and 20 follicles, which are the infant form of the ovum. Only one of the follicles reach full maturity and is referred to as the Graafian follicle. When this follicle has fully developed it ruptures and discharges a mature egg inside the ovary near a fallopian tube. During this stage, after rupture but before entering the fallopian tube, the ovum is referred to as the corpus luteum. At this point, the corpus luteum releases massive amounts of progesterone and estrogen. It is this secretion which causes the glands in the endometrium to release nutrients to sustain the forthcoming fertilized egg. Once the egg enters the fallopian tube it is primed for fertilization from a sperm cell received during coitus. If the egg is fertilized it will become a zygote and hopefully implant itself in the uterine wall.
During the actual act of fertilization, the combining of the egg and sperm, 23 chromosomes from the male and 23 chromosomes from the female combine to make a genetically unique individual. The male sex cell contains either an X or a Y chromosome, which determines the sex of the new individual. Since the egg can only survive for a few days, it is usually fertilized in the infundibulum. This section of the fallopian tubes is just a couple of inches from the ovaries.
In conclusion, both secret agents arrived at the final destination together. Never mind that one had to conduct a cross-country marathon to arrive at the destination and the other only had to walk down the street. The point is that they both arrived safe and intact, despite great distances and against great odds. Now they can enjoy their 9-month honeymoon, at which time they will enter the real world.
Finchner-Rathus, L., Nevid, J.S., Rathus, S.A. (2005). Human sexuality in a world of diversity, sixth edition. Boston, MA: Allyn & Bacon.