Fertilisation and implantation

Summary

This video explains the process of fertilization and early human development. It covers ovulation, where the egg is released into the uterine tube and the corpus luteum secretes progesterone to prepare the uterus for implantation. If fertilization occurs, sperm travel through the female reproductive tract to reach the egg, forming a zygote. The zygote undergoes cell division, becoming a morula and then a blastocyst. The inner cell mass forms the embryo (baby), while the trophoblast forms the placenta and secretes hCG to maintain progesterone production. This hormone supports uterine lining integrity and is detectable in pregnancy tests, ensuring early development is sustained.

Takeaways

• 😀 Ovulation occurs around day 14 of the menstrual cycle when the egg is released from the ovary into the uterine tube.
• 😀 The released egg is captured by finger-like projections called fimbriae and moves towards the infundibulum in the uterine tube.
• 😀 After ovulation, the ruptured follicle turns into the corpus luteum, which releases progesterone to prepare the uterine wall for implantation.
• 😀 The corpus luteum continues to release progesterone for about 10 days, assuming fertilization and implantation will occur.
• 😀 If fertilization does not occur, the corpus luteum stops releasing progesterone, and the uterine lining begins to break down, leading to menstruation.
• 😀 Fertilization occurs when sperm enters the vagina, with around 200-500 million sperm being deposited.
• 😀 Only about 500 sperm reach the infundibulum of the uterine tube, and only one sperm successfully penetrates the egg's zona pellucida.
• 😀 The fertilized egg forms a zygote, which begins to divide and develop into a multi-cellular structure called a morula by day 3 or 4.
• 😀 By day 5 or 6, the morula forms a blastocyst, which consists of an inner cell mass (embryoblast) that will form the baby and an outer layer (trophoblast) that will form the placenta.
• 😀 Upon implantation, the trophoblast releases the hormone HCG (human chorionic gonadotropin), signaling the corpus luteum to continue progesterone production and maintain the uterine lining.

Q & A

What happens to the egg after it is released from the ovary?

After being released from the ovary, the egg enters the uterine tube, specifically the infundibulum, where it may encounter sperm for fertilization.

What role does the corpus luteum play after ovulation?

The corpus luteum forms from the structure that released the egg and releases progesterone, which prepares the uterine lining for possible implantation of a fertilized egg.

How long does the corpus luteum continue to release progesterone?

The corpus luteum continues to release progesterone for about 10 days, assuming that the egg will be fertilized and implant itself into the uterine wall.

What happens if fertilization does not occur after 10 days?

If fertilization does not occur, the corpus luteum stops releasing progesterone, which leads to the breakdown of the uterine lining, causing menstruation.

How many sperm are typically ejaculated into the vagina during intercourse?

Approximately 200 to 500 million sperm are ejaculated into the vagina during intercourse.

Why is the vagina hostile to sperm?

The vagina is acidic, which kills off many sperm, leaving only a small percentage that can survive and continue their journey toward the egg.

How many sperm typically reach the uterine tube, and why is this number so small?

Out of the millions of sperm ejaculated, only around 500 make it to the uterine tube, as many are killed off by the vaginal acidity, while others are unable to navigate the reproductive tract.

What happens once one sperm successfully penetrates the egg?

Once a sperm penetrates the egg's zona pellucida, no other sperm can enter, and the DNA from both the sperm and egg combine to form a zygote.

What is the significance of the blastocyst stage in pregnancy?

The blastocyst, which forms around days 5–6, consists of an inner cell mass (which will become the embryo) and an outer trophoblast (which will form the placenta). This structure is crucial for implantation into the uterine wall.

How does hCG (human chorionic gonadotropin) help sustain pregnancy?

hCG is released by the trophoblast cells of the blastocyst after implantation, and it signals the corpus luteum to continue producing progesterone, which maintains the uterine lining and supports the pregnancy.