Conception & Fetal Development.docx

Conception

The union of a single egg and sperm forming a baby.

Gametogenesis

The process of forming gametes (sperm and ova).

Spermatogenesis

The process of sperm formation, beginning during puberty in males.

Mitosis

The replication of cells to maintain the same number of chromosomes (46).

Meiosis

The division process that reduces the chromosomal number from diploid (46 chromosomes) to haploid (23 chromosomes).

Oogenesis

The process of egg (ova) formation in females, starting during fetal life.

Ovulation

The release of a mature ovum from the ovary, typically occurring on day 14 of a 28-day cycle.

Graafian Follicle

The ruptured follicle that secretes estrogen and progesterone to maintain pregnancy.

Fertilization

The process when a sperm enters the ovum, usually occurring in the ampulla of the fallopian tube.

Zona Reaction

A change in the zona pellucida that prevents other sperm from entering the ovum after fertilization.

Zygote

The fertilized ovum that forms after the sperm and ovum nuclei merge.

Morula

A solid ball of 12-16 cells formed by day 3 after conception.

Blastocyst

A structure formed from the morula that develops into two distinct layers:the embryoblast and trophoblast.

Monozygotic Twins

Identical twins resulting from one ovum and one sperm, always the same gender.

Dizygotic Twins

Fraternal twins resulting from two ova and two sperm, may be the same or different genders.

Implantation

The process where the blastocyst attaches to the endometrium of the uterus.

Decidua

The modified endometrium during pregnancy that provides a rich environment for implantation.

Amniotic Fluid

The fluid surrounding the baby that protects and promotes normal fetal development.

Umbilical Cord

The structure extending from the umbilicus to the placenta, containing two arteries and one vein.

Placenta

An organ that sustains pregnancy and facilitates nutrient and gas exchange between mother and fetus.

Human Chorionic Gonadotropin (hCG)

A hormone that preserves the function of the corpus luteum during early pregnancy.

Germinal Stage

The first two weeks after conception, from fertilization to the formation of the embryonic disc.

Embryonic Stage

The period from day 15 to 8 weeks after conception, where major organ systems form.

Fetal Stage

The period from week 9 to birth, characterized by growth and development of organ systems.

Ectoderm

The outer germ layer that forms skin, nails, and the nervous system.

Mesoderm

The middle germ layer that forms connective tissues, muscles, and the vascular system.

Endoderm

The inner germ layer that forms the epithelial linings of the GI and respiratory tracts.

Cephalocaudal Development

The principle that development occurs from head to toe.

Peripheral Development

The principle that development occurs from the center of the body outward.

Teratogens

Harmful substances that can cause developmental abnormalities during the embryonic stage.