11.4c Fertilization

19/03/2013 § Leave a comment

Part 5 (blog 5) is when we start piecing things together and forming a baby! Not literally, of course because that would be really consequential and kind of really stupid. But that’s what fertilization does – it makes a baby! In humans, fertilization is when the egg cell (produced by oogenesis) and the sperm cell (produced by spermatogenesis) fuse to create an embryonic cell.

The process of fertilization can be explained in six steps, as well as a few important vocabulary. As always. HERE WE GO.

  • the zone pellucida is the coat made up of glycoprotein that protects the egg cell
  • the acrosome as we know by now (or should, at least) is the head of the sperm cell, and essentially a membrane-bound sac of enzymes
  • inside the egg cell, near the membrane, are cortical granules, which are vesicles whose contents are important after fusion
  • the cortical granules, after fertilization, will release its contents from the egg by exocytosis, which will interact with the glycoproteins from the previously mentioned zone pellucida and turn into an impenetrable membrane called the fertilization membrane
  • the blastocyst is what we call the embryo after 48 hours, when it continues to divide and looks like a hollow ball
  • finally, implantation is when the blastocyst starts to obtain food and nutrients from the mother by sinking into the endometrium (the uterus lining!)

An Embryo’s Six Steps to Success (A Quick Guide Written By Something That Is Not An Embryo)

  1. Sperm Arrival: Basically, one lucky sperm cell reaches the egg, having been attracted by a chemical signal.
  2. Binding: Using the components of its zone pellucida, the sperm breaks triggers the acrosome reaction.
  3. The Acrosome Reaction: The acrosome’s contents are released after the acrosomal cap is removed. Enzymes called proteases are released to digest a path (think that they’re digging into the earth, ahahah) to create a path for the sperm to reach the plasma membrane of the egg cell.
  4. Fusion: In which the sperm and egg nuclei finally meet up after their respective plasma membranes also fuse. This results in cortical reaction.
  5. Cortical Reaction: Almost like flicking a switch on in the egg. The cortical granules release their contents (including enzymes) by exocytosis, and the enzymes help to create a harder coating to prevent any more sperm from entering.
  6. Mitosis: Both nuclei (from the egg and sperm) don’t fuse quite yet. They instead do a few rounds of mitosis to produce a two-cell embryo. More information on that… later?

…I wonder if the number of essay questions for this unit have diminished yet…

Essay Questions

  1. Draw a labelled diagram of the adult female reproductive system. 4 marks
  2. Draw a labeled diagram of an adult male reproductive system. 6 marks
  3. Explain the processes involved in oogenesis in humans. 9 marks
  4. Draw the structure of a mature human egg. 4 marks
  5. Explain the role of hormones in the regulation of the menstrual cycle in human females. 8 marks
  6. Outline the levels of each of the hormones that control the menstrual cycle immediately before ovulation. 3 marks
  7. Explain the roles of LH and FSH in the menstrual cycle, including the timing of their secretion during the cycle. 6 marks
  8. Outline the roles of progesterone and estrogen in the human menstrual cycle. 6 marks
  9. Draw a labeled diagram of the structure of an ovary as seen using a light microscope. 5 marks
  10. Draw the structure of the human female reproductive system immediately before ovulation. (Only the ovaries, oviducts and uterus need to be shown.) 6 marks
  11. Draw a labelled diagram of a mature sperm. 5 marks
  12. Outline the process of spermatogenesis in humans. 5 marks
  13. Production of semen involves a series of processes, which in total take many weeks to carry out. Outline the processes involved in semen production from the start of sperm formation (spermatogenesis) to ejaculation. 8 marks
  14. Compare the process of spermatogenesis and oogenesis. 7 marks
  15. Discuss how, in humans, a larger number of sperms are produced than eggs. 4 marks
  16. Describe the process of fertilization in humans. 8 marks
  17. Describe the development of the early human embryo. 5 marks
  18. Outline the regulation of pregnancy by two named hormones. 4 marks
  19. Outline the role of human chorionic gonadotropin (HCG) in early pregnancy 2 marks
  20. Outline the way in which a pregnancy can be detected at a very early stage. 4 marks
  21. Compare the roles of LH and HCG in female reproduction. 2 marks
  22. State the role of the amniotic sac and the amniotic fluid. 2 marks
  23. Explain the function and structure of the placenta. 8 marks
  24. Outline the process of in vitro fertilization (IVF). 6 marks
  25. Discuss the ethical issues surrounding IVF. 6 marks
  26. Outline the role of positive feedback in the process of birth in humans. 4 marks


DATA BASED QUESTIONS « now showing at re: still faster than you! »

Page 282, maternal age and pregnancy

1. Describe the trend in the percentage of live births as the age of the mother increases. —> As the age of the mother increases, the percentage of total live births start to decrease. This means that the older the mother is, the less likely her child will survive birth. The decrease in percentage of live births is at first gradual, but after hitting around 44 years old, the percentage suddenly drops a significant amount, from 52.5% to 17.2%, more than 30% different, compared to the constant 1% – 9% change in between 12 years old to 39 years old.

2. Explain this trend, using the data in Table 5. —> The decrease of live births can be associated with the increase of miscarriages. The general trend of miscarriage as the mother gets older is that there are more miscarriages. This coheres with the decreasing amount of live births. There is also a definite increase in ectopic pregnancy (whatever that is, I’m sorry). 

3. A small percentage of the mothers were younger than 15. They had a miscarriage rate higher than 20%. Suggest reasons for this. —> This small percentage of mothers are probably not in the healthiest or best environment to raise a baby at such a young age, therefore they wouldn’t have a good hospital to help them along child birth. Because of this, the birth would be very difficult, and the baby could easily die. Also, if they’re younger than 15, God knows what else they could be doing if they’re already getting pregnant (e.g. substance abuse, physical abuse) and the stress could cause a miscarriage.

4. Suggest two reasons for the difference in percentage of college-educated mothers in the two age groups. —> Mothers with a college education seem to normally get pregnant at an older age (but not too old) because they would normally seek a job after college, and wouldn’t have the time or income to support a baby. Those who got pregnant at a younger age may have gotten … lost along the way.

5. Discuss whether there is an ideal age at which to have children. —> It goes both ways, wherein the mother shouldn’t be too young and shouldn’t be too old. The mother shouldn’t be too young because she wouldn’t have enough of an education to get a job in order to support herself and the baby, nor would she be mature enough or ready for that kind of responsibility. At the same time, if the mother is too old, then there are multiple genetic risks to the baby, so it’s also important not to wait too long. It is then best to have children somewhere in the middle of too young and too old, and it seems like these years are the late 20s to mid 30s, where a woman is both prepared and healthy enough to raise a kid.

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