– Human fertilisation and early development

Question 1

Where in the uterine tube does fertilization occur? What does the infundibulum do?

Answer 1

Fertilization typically occurs in the ampulla, which is the middle portion of the uterine tube. The infundibulum, which is the funnel-shaped opening at the distal end of the uterine tube, helps capture the released egg (oocyte) from the ovary and guide it into the ampulla for potential fertilization

Question 2

How do progesterone and estrogen impact ciliary beating in the oviduct?

Answer 2

Progesterone decreases ciliary beating in the oviduct, while estrogen increases it. The coordinated ciliary movement helps transport the egg and sperm through the oviduct. Progesterone, produced during the luteal phase of the menstrual cycle, slows down ciliary beating, allowing the oocyte to have sufficient time for potential fertilization. Estrogen, on the other hand, increases ciliary activity to aid in the transportation of the egg and sperm

Question 3

Where does sperm maturation occur? What is the critical process required for sperm to become fertile?

Answer 3

Sperm maturation occurs in the epididymis, a coiled tube located on the back of each testicle. The critical process required for sperm to become fertile is called capacitation. Capacitation involves the removal of the sperm’s protective coating and the alteration of its membrane, making it more capable of penetrating and fertilizing the egg.

Question 4

What initiates the acrosome reaction in sperm?

Answer 4

The acrosome reaction in sperm is initiated by the binding of sperm to the zona pellucida, a glycoprotein layer surrounding the egg. This binding triggers a series of biochemical reactions which includes an influx of calcium ions that result in the release of enzymes from the acrosome, enabling the sperm to penetrate the zona pellucida and reach the egg.

Question 5

During fertilization, what is required to preserve euploidy in the newly formed zygote?

Answer 5

To preserve euploidy (the correct number of chromosomes) in the newly formed zygote during fertilization, proper meiotic division is essential. Both the egg and sperm must undergo meiosis, which ensures the reduction of chromosomes by half, resulting in a haploid state. When the sperm fuses with the egg, the zygote will have the correct number of chromosomes, maintaining euploidy.

Question 6

Describe the cells within a blastocyst. Which cells will form the fetus? Which cells will form the placenta?

Answer 6

A blastocyst consists of two main cell types: the inner cell mass (ICM) and the trophoblast cells. The ICM, located within the blastocyst, gives rise to the fetus. It will develop into the embryonic disc, which eventually forms the various tissues and organs of the developing organism. The trophoblast cells form the outer layer of the blastocyst and play a crucial role in implantation. They give rise to the placenta, which provides the necessary support and nutrients to the developing fetus.

Question 7

What are the 10 Steps of acrosome reaction and sperm penetration

Answer 7

1. Enzymes on the surface of sperm digests the matrix between the cumulus cells
2. Sperm head then binds to zona pellucida causing sperm membrane Calcium channels to open
3. Calcium then flows into the sperm triggering acrosome reaction
4. The calcium influx also triggers release of acrosin enzymes to digest the zona pellucida
5. The acrosomal enzymes then form many holes in ZP
6. Once a path is formed in the ZP, 1 sperm forcibly swims towards oocyte membrane (oolemma)
7. The sperm membrane then binds to the oolemma
8. The oocyte and sperm membranes then fuse
9. Only the sperm, nucleus and centrioles enter the oocyte
10. Sperm cells membrane, tail, and mitochondria is left behind