When an oocyte and spermatozoa fuse, the process is referred to as fertilization. The gametes are haploid at that stage and grow further into a diploid zygote. There is a difference in the forms that the process can be made possible. It can be through the natural mode that occurs in vitro or can happen outside the body in vivo (Hill, 2016). Research studies have been done adequately to ensure that circumstances that support life out of the womb can be created for a while before a transfer is done to the womb for future growth and development. For fertilization to occur oogenesis and sperm capacitation, have to take place. Then they fuse, and migration occurs to the uterus where the fetus develops.
According to Wasserman, Jovine, and Litscher, chemotaxis takes place after ovulation to help the sperm move towards the egg and aid in fertilization, and therefore, it is not a matter of chance for the spermatozoa to reach the oocyte (2001). Then it binds with the Zona pellucida as the first step. An acrosome of the sperm then occurs in step two also referred to as cellular exocytosis, which penetrates the extracellular coat in step three to reach the perivitelline space. In step four, the sperm has to bind to the plasma membrane and eventually fuse with it in step five causing the formation of a zygote. In a study done by Wassarman, Jovine and Litscher (2001) on mouse eggs, the process took 90 minutes to be completed.
Pregnancy takes 40 weeks from the first day of the last monthly period to mature for delivery. In the first trimester, which lasts for the first 12 weeks of the pregnancy and is hard for most women has plenty of events that take place in the womb. According to Mustafa (2012), hormonal changes affect most of the organs in the body. The first sign is the missing of the period of the month of conception. It leads to a test to confirm the pregnancy. Human chorionic gonadotropin is the hormone that indicates pregnancy and can be detected using simple tests for as early as three weeks post conception, Allyn & Bacon, (2008).
Other changes may include; feeling tired all the time. Tenderness of the breasts as blood is directed to the breast to start preparation for breastfeeding. Mood swings which are promoted by the increased production of various hormones. A change in taste senses is also noted. This shift is the primary cause of nausea and vomiting for most of the women. It may also promote pic which is a deficiency that leads to eating of unnatural things like stones.
In the second trimester Lasting up to 28 weeks of the pregnancy, some of the symptoms that were present in the previous one start to fade off while new ones develop. The main one at this point is that as the baby continues to grow so does the womb and hence the abdomen. Stretch marks are bound to develop from the skin that is stretching as well. Some of this discomforts continue into the third trimester, which begins from week 29 to 40 for many people. The enlarged abdomen then leads o heavy breathing. Pressure is applied to the bladder and hence increased visits to the toilet. In the upper side of the abdomen, the pressure causes heartburn and increased acidity. The mother experiences difficulty in sleeping due to lack of comfortable sleeping position.
Reference
Allyn & Bacon (008). Conception, Pregnancy, and Childbirth. Copyright PPT.
Hill, M.A (2016). Embryology. Fertilization. Retrieved from https://embryology.med.unsw.edu.au/embryo/index/php/fertilization
Mustafa, A. (2012). Pregnancy Slideshow. Slideshare. Retrieved from http://www.slideshare.net/arina_mustafa/pregnancy-slideshow-13869282
Wassarman, P. M., Jovine, L. & Litscher, E. S. (2001). A Profile of Fertilization in Mammals. Nature Cell Biology. Doi:10.1038/35055178
