Describe fertilization, with reference to how the sperm enters the Assignment

Describe fertilization, with reference to how the sperm enters the oocyte. Explain the key changes that occur in the female during each of the three trimesters of pregnancy - Assignment Example Fertilization occurs during the union of the male sperm and the secondary oocyte producing a zygote. A zygote is the fertilized egg that develops into a fetus. The secondary oocyte has the female chromosome X whereas the sperm has both female (X) chromosome and Male (Y) chromosome. Oocytes must be supplied with various molecules needed for the growth of the embryo. A female undergoes various changes during pregnancy. These are known as trimesters consisting of three stages over the 9 month or 40 week pregnancy period. The fetus undergoes different changes in each of the three stages until it fully develops. The first trimester is the period up to 13 weeks of the pregnancy. It is the most crucial stage of the pregnancy. The female body undergoes many changes. The body structure and organs of the fetus begin to develop. This includes the eyes, mouth, ears, throat and skin. The fetus is surrounded by the amniotic sac. The placenta is developed and transfers nutrients from the mother to the baby and waste from the baby to the mother. The body of the pregnant mother undergoes changes signified by certain symptoms. These symptoms include nausea also know as morning sickness, fatigue, frequent urination and softness of breasts. Spotting or normal bleeding is common as the fetus is implanted firmly in the uterus. The experiences at this stage vary wit h different women. Some women are very tired during this stage whereas others are full of energy. It is at this stage that miscarriages, birth defects or ectopic pregnancies can occur (Tortora & Derrickson, 2009). The second trimester is from 14 to 26 weeks. This is a pleasurable time of the pregnancy. All the symptoms experienced in the first trimester are gone. There is no morning sickness and fatigue. Most pregnant mothers start planning for the birth of their baby at this stage. They sleep better and have more energy. Different symptoms develop; back pain and abdominal pain due to the increase in weight of the fetus.