Oogenesis (Formation of Egg Cells) - Reproductive System In Humans

Summary

This video explains oogenesis, the process of female egg cell formation that begins before birth. Girls are born with 200,000 to 2 million primordial cells, but only about 40,000 remain by puberty, and only 400 will mature. Oogenesis involves the development of follicles, from primordial to primary to secondary follicles, and the division of oogonia into primary oocytes. These undergo meiotic divisions, producing secondary oocytes, polar bodies, and eventually an ootid that differentiates into a mature egg. The egg is then ovulated, ready for fertilization. This process is key to understanding female reproduction.

Takeaways

• 😀 Oogenesis is the process of forming female sex cells (eggs or ova) in the ovaries.
• 😀 Unlike spermatogenesis, which starts at puberty in males, oogenesis begins before birth in females.
• 😀 Girls are born with 200,000 to 2 million primordial eggs, but only about 40,000 remain at puberty.
• 😀 Only 400 eggs will fully mature during a woman's reproductive life.
• 😀 One mature egg is ovulated (released) from the ovary during each menstrual cycle.
• 😀 Inside the ovary, the egg is housed in a follicle that grows from a primordial follicle to a mature one.
• 😀 The development of the egg involves the division of primordial cells by mitosis to form oogonia, which then become primary oocytes.
• 😀 The primary oocyte undergoes a meiotic division to form a secondary oocyte and a polar body.
• 😀 The secondary oocyte undergoes a second meiotic division to produce an ootid and another polar body.
• 😀 At the end of oogenesis, one haploid ovum and three polar bodies are formed, but only the egg cell is viable for fertilization.

Q & A

What is oogenesis?

Oogenesis is the process of forming female sex cells, or eggs (ova), in the ovaries. It involves several stages of cell division and differentiation to produce a mature egg that is capable of being fertilized.

How is oogenesis different from spermatogenesis?

Oogenesis occurs in females and begins before birth, while spermatogenesis occurs in males and begins at puberty. Oogenesis results in one mature egg per cycle, whereas spermatogenesis produces millions of sperm cells continuously after puberty.

When does oogenesis begin?

Oogenesis begins before girls are born. Females are born with a set number of primordial eggs that will mature over time.

How many eggs are present in a female before birth?

Females are born with approximately 200,000 to 2 million primordial eggs in their ovaries.

How many eggs are present when girls reach puberty?

By puberty, only about 40,000 eggs remain in the ovaries.

How many eggs mature during a woman's reproductive life?

Only about 400 eggs will mature and be ovulated over a woman's reproductive life.

What happens to the eggs in the ovaries as a woman ages?

As a woman ages, the number of eggs in the ovaries decreases, and fewer eggs are available for ovulation. Most of the eggs undergo atresia (degeneration).

What is a primordial follicle?

A primordial follicle is a small structure in the ovary that contains an immature egg. It is the initial form of the follicle before it starts maturing.

What is the role of meiotic divisions in oogenesis?

Meiotic divisions in oogenesis reduce the chromosome number of the egg. The primary oocyte undergoes the first meiotic division to form a secondary oocyte and polar body, and the secondary oocyte undergoes the second meiotic division to form an ootid and another polar body.

What are polar bodies and what happens to them?

Polar bodies are small cells produced during meiotic divisions in oogenesis. They contain a haploid set of chromosomes but are non-functional. They eventually degenerate and do not contribute to fertilization.