Overview
This lecture explains the processes of fertilization and implantation, tracing the journey from gamete fusion to early embryo development and the establishment of pregnancy.
Fertilization Process
- Fertilization occurs in the fallopian tube after ovulation releases a mature egg.
- Sperm are attracted to the egg by chemical signals and compete to penetrate it.
- Only one sperm successfully burrows into the egg; its head containing the nucleus enters.
- The nuclei of the sperm and egg fuse to form a diploid zygote (combining two haploid cells).
- This fusion restores the full set of chromosomes in the zygote.
Zygote Development
- The zygote undergoes mitosis (cell division), forming two, four, eight, etc., cells.
- Continued mitosis creates a solid ball of cells called the morula.
- The developing embryo is moved along the fallopian tube by cilia towards the uterus.
Formation of Blastocyst and Implantation
- The morula becomes a blastocyst—a hollow ball of cells with distinct layers.
- The blastocyst consists of an outer trophoblast (forms skin/nervous system) and inner cell mass (forms internal organs).
- The blastocyst implants into the thickened, vascular endometrium of the uterus.
- Implantation into the endometrium marks the onset of pregnancy.
Key Terms & Definitions
- Fertilization — Fusion of egg and sperm nuclei to form a diploid zygote.
- Zygote — A single diploid cell formed after fertilization.
- Mitosis — Cell division process that increases cell number in the developing embryo.
- Morula — Solid ball of cells from early mitotic divisions.
- Blastocyst — Hollow ball of cells with outer trophoblast and inner cell mass.
- Implantation — Embedding of the blastocyst into the uterine lining (endometrium).
- Trophoblast — Outer layer of the blastocyst, forms external tissues.
- Endometrium — Lining of the uterus where implantation occurs.
Action Items / Next Steps
- Review and label diagrams of egg, sperm, and stages of embryo development.
- Study the stages and significance of meiosis and mitosis.
- Prepare flashcards using the key terms for revision.
- Watch recommended videos on meiosis, spermatogenesis, and oogenesis for deeper understanding.