Oogenesis, Ovulation, Fertilization, and Embryonic Development

Study Notes

Oogenesis is the process of forming a mature ovum from oogonia, starting before birth in females.
Primordial germ cells appear around the fourth week of development in the uterus, proliferating through mitosis.
Primordial germ cells migrate to the developing female gonads and eventually become oogonia.
Oogonia are diploid cells with 46 chromosomes, produced through mitosis from primordial germ cells.
Oogonia multiply by mitosis, producing more oogonia with the same genetic material.
Some oogonia degenerate, while others enlarge and stop mitotic division, becoming primary oocytes.
Primary oocytes are diploid cells with 46 chromosomes, preparing to start meiosis.
Before birth, all oogonia have transformed into primary oocytes, totaling around 2 million at birth.
After birth, most primary oocytes remain arrested in diplotene stage and many degenerate.
Around puberty, a pool of growing primordial follicles is maintained in the ovaries, with about 5 to 15 starting to grow each month.- The text discusses the process of ovulation, fertilization, and early embryonic development.
During ovulation, the secondary oocyte along with cumulus cells is released from the ovary into the fallopian tube.
If the secondary oocyte is not fertilized within 24-48 hours, it disintegrates and gets absorbed by the fallopian tube epithelium.
When the sperm fertilizes the secondary oocyte, it completes its second meiotic division and forms a definitive ovum with 23 chromosomes.
The definitive ovum is haploid with single structured chromosomes, ready for fertilization.
Upon fertilization, the sperm brings 23 chromosomes which combine with the ovum's chromosomes to form a zygote with 46 chromosomes.
Genetic sex is determined at fertilization - XX chromosomes result in a female, while XY chromosomes result in a male.
Sperm also brings molecules that activate the metabolic machinery of the ovum, making the zygote metabolically active for further development into an embryo.

Description

Learn about the process of oogenesis in females, from the formation of oogonia to the release of a definitive ovum. Explore the stages of ovulation, fertilization, and early embryonic development after the fusion of sperm and ovum. Understand how genetic sex is determined at fertilization and the activation of metabolic machinery in the zygote.