Advanced Physiology and Anatomy

Human Fertilization

Human fertilization is the union of sperm from the paternal origin with an egg, ovum, from the maternal origin, resulting in a fertilized egg, scientifically known as a zygote cell. The fertilized egg then grows in the mother's womb until the child is conceived. This commonly happens within the fallopian tube. Since the fertilization process is intricate and comprises several phases that eventually result in human life, the paper will simply outline how sperm and egg combine to generate a fertilized egg. Human fertilizationis initiatedby a woman's menstrual cycle, where the period prepares the body for fertilization. In the cycle is where an egg cell is released, in a process known as ovulation; into the fallopian tube where fertilization occurs (Carlson, 2012).

Challenges of Sperm Cells

In the course of intercourse, men ejaculate semen, sperms, into women vaginas. A single ejaculation is believed to contain around 150 million sperm cells; naturally, the sperm cells are chemically attracted to the fallopian tube with the aim of interacting with the egg cell. Nevertheless, the sperms face a couple of challenges before reaching the egg cell. Not all the 150 million cells will make it to the egg cell, the majority of about 85% will die along the way and the one that will make it has only 12 to 48 hours to fuse with the ovulated egg. Although just one cell is needed to fertilize the egg, the rest of the 15% of sperms will chemically find their way to the uterus, famously known as the womb. Once the sperm cells are into the uterus, choosing the appropriate fallopian tube becomes difficult, since only one of the two fallopian tubes contains the ovulated egg (Tanaka, Nagayoshi & Kusunoki, 2012). By the time the sperms are reaching the ovulated egg, only a few sperm cells out of the 150 million sperm cells reach the ovulated egg. The race to fertilize the egg intensifies and just one cell will finally fertilize the egg, and the remaining cells will surround the now fertilized egg. Once the first sperm fuses with the egg, it releases enzymes to breakdown the egg's cell membrane, to enable it to penetrate into the egg, thus fertilization. The ovulated egg literally waits for only one sperm cell from the 150 million cell ejaculated; the sperm cell begins to race wildly towards the egg cell, and the winner will eventually unite with the egg cell to create human life.

Oogenesis versus Spermatogenesis

Oogenesis and Spermatogenesis are forms of reproductive divisions experienced in animal, mammals' sexual reproduction. The processes are scientifically known as gametogenesis which occurs in a germ cell of the gonads through the process of meiosis. This process involves the formation of gametes, both male gametes, sperms and female gamete an egg. The two processes have both similarities and differences: even so, the main difference between the two processes is oogenesis is the formation of egg cells from the germ cells oogonia in females while spermatogenesis is the formation of the sperm cells from the germ cells and spermatogonia in males. The paper will further briefly tackle on the various similarities and difference of the two processes: In mammals, spermatogenesis originates from a spermatocyte in the male testes, while oogenesis begins from a primary oocyte in the ovaries in females (Foster & Hughes, 2011).

Comparison of Oogenesis and Spermatogenesis

Furthermore, spermatogenesis effects four spermatozoa which are functional from the primary spermatocyte while on the other hand, oogenesis results in only one ovum with three polar bodies from the primary oocyte. Again, two remarkably different cells are formed in oogenesis while in spermatogenesis two identical sized cell are formed. Also, sperm cells are motile and much larger as compared to ova which are smaller in size and are immotile (Hunt & Hassold, 2002). The whole process of spermatogenesis is finished inside the testis in males while in females, the process of oogenesis continues outside the ovary, as secondary maturation takes place in the oviduct. Lastly, Spermatogenesis starts at puberty and results in the production of billions of sperm at once as compared to oogenesis which can even begin before birth, in the stages of embryonic development and results in producing only one cell, ovum every month. In other terms, spermatogenesis comprises of short growth phases which are continuous as compared to long growth phases which are cyclical experienced in oogenesis.

Effects of Estrogen and Testosterone on the Body

Estrogen refers to all the chemically identical hormones; estradiol (the critical hormone for reproduction in women), estriol, and estrone. Estrogens are hormones that play significant and vital roles in reproduction and sexuality in women. A more substantial number of estrogen hormones are produced by the woman's ovaries although a small amount of the hormones also produced by the adrenal glands and other fat cells. Estrogen is responsible for secondary sex features in females during the puberty stage; these features include wider hips, pubic hair, skin, breasts and even armpit hair (Klump, Keel, Racine, Burt, Neale & Hu, 2013). Another vital role of the hormone is regulating the menstrual cycle and the growth of uterine lining during the menstrual cycle. Moreover, in the instance the egg is not fertilized, the body decreased estrogen levels, and menstruation ensues. On the other hand, if the egg is fertilized, estrogen together with progesterone will stop ovulation from occurring during the period of pregnancy. Estrogen plays the role of blood clotting accompanied by maintaining vaginal wall's thickness and strength, vaginal lubrication, and urethral lining. Also, estrogen is responsible for regulating lactation and other breast changes experienced during pregnancy and adolescence stage.

Testosterone hormone is the male sex hormone responsible for reproduction and sexual development in men. Female also produces testosterone but in small amounts as compared to men. Testosterone hormones are classified as androgens or steroids; the hormone is majorly produced in the testes and small quantities in other glands like adrenal glands. Its production is controlled by the hypothalamus of the brain and the pituitary glands. The brain dictates the amount of testosterone produced by the pituitary glands to the testes conveyed chemically in the bloodstream (Finkelstein, Lee, Burnett-Bowie & Leder, 2013). Testosterone begins production before birth; in the formation sex organs in males, during puberty; development of secondary sex features such as the increased size of the penis and testis, deepened voice, and body and facial hair. Furthermore, the hormone is responsible for sperm production, sex drive, red cell formation, maintenance of muscles and fat distribution. Testosterone is directly linked to the overall health and well-being of males.

Conclusion

In conclusion, fertilization is a complicated process which involves the union of sperm from the paternal origin with an egg, ovum, from the maternal origin ensuing to a fertilized egg, scientifically referred to as a zygote cell, which matures in the mother's womb until birth. The paper also briefly compares the differences and similarities of the and Spermatogenesis processes; where oogenesis is the process involved in the formation of the egg, ovum in the ovaries in females while Spermatogenesis is the process involved in the creation of sperm cells in the testes in males. Lastly, the paper has described the effects of the estrogen hormones in females and the roles they play and at the same time tackling the impact of testosterone in males. Furthermore, it can be stated that testosterone is responsible for the overall health and well-being of men.

References

Carlson, B. M. (2012). Human Embryology and Developmental Biology E-Book: with STUDENT CONSULT Online Access. Elsevier Health Sciences.

Tanaka, A., Nagayoshi, M., Tanaka, I., & Kusunoki, H. (2012). Human sperm head vacuoles are physiological structures formed during the sperm development and maturation process. Fertility and sterility, 98(2), 315-320.

Foster, W. G., & Hughes, C. L. (2011). Gene expression in oogenesis and implications for transgenerational effects of environmental toxicants. Biology of reproduction,84(1), 2-4.

Hunt, P. A., & Hassold, T. J. (2002). Sex matters in meiosis. Science, 296(5576), 2181-2183.

Klump, K. L., Keel, P. K., Racine, S. E., Burt, S. A., Neale, M., Sisk, C. L., ... & Hu, J. Y. (2013). The interactive effects of estrogen and progesterone on changes in emotional eating across the menstrual cycle.Journal of abnormal psychology, 122(1), 131.

Finkelstein, J. S., Lee, H., Burnett-Bowie, S. A. M., Pallais, J. C., Yu, E. W., Borges, L. F., ... & Leder, B. Z. (2013). Gonadal steroids and body composition, strength, and sexual function in men. New England Journal of Medicine, 369(11), 1011-1022.