NCM 107: Stages of Fetal Development

Vocabulary flashcards covering pre-embryonic, embryonic, and fetal development stages, organogenesis, germ layer differentiation, and gestational milestones.

Pre-embryonic Stage

The first stage of fetal development spanning the first $2\,\text{weeks}$ after fertilization, during which the zygote undergoes cleavage and implantation occurs.

Embryonic Stage

The development period from week $3$ through week $8$ characterized by organogenesis and primary germ layer formation, ending when the embryo is about $3\,\text{cm}$ long with a human appearance.

Fetal Stage

The period of development from week $9$ (or the $9\text{th}$ week) until birth, marked by rapid growth and the maturation of organs and tissues.

Fertilization

The process where a sperm cell penetrates and fuses with an ovum in the fallopian tube within a $24\text{--}48\,\text{hour}$ window, resulting in a single-celled zygote.

Zygote

A single cell containing genetic material from both parents formed immediately after chromosomal fusion, which lasts for $3\text{--}5\,\text{days}$.

Cleavage

The series of rapid mitotic cell divisions undergone by the zygote as it moves through the fallopian tube toward the uterus.

Morula

A solid ball of about $16\text{--}32\,\text{cells}$ formed by Day $3\text{--}4$ after fertilization, named after the Latin word for mulberry.

Blastocyst

A fluid-filled structure formed by Day $5\text{--}6$ after fertilization consisting of an inner cell mass and a trophoblast layer.

Inner Cell Mass

The internal cluster of cells within the blastocyst that eventually forms the embryo.

Trophoblast

The outer cell layer of the blastocyst that invades the uterine lining to secure the embryo and form the placenta and membranes.

Implantation

The process occurring around Day $6\text{--}10$ (or $8\text{--}10\,\text{days}$) post-fertilization where the blastocyst attaches to and embeds into the endometrium.

Organogenesis

The critical process during the embryonic stage (and 1st trimester) in which all major organs and body structures begin to form.

Ectoderm

The outer primary germ layer that gives rise to the skin and nervous system, forming the neural tube during the $3\text{rd}\,\text{week}$.

Mesoderm

The middle primary germ layer that forms muscles, bones, and the cardiovascular system, with the heart beginning to beat by the $4\text{th}\,\text{week}$.

Endoderm

The inner primary germ layer responsible for developing into the gastrointestinal (GI) tract, lungs, and bladder.

Quickening

The maternal perception of fetal movements, which typically begins between weeks $13\text{ and }16$ of pregnancy.

Lanugo

Fine hair that covers the body of the fetus between weeks $17\text{ and }20$ of fetal development.

Surfactant

A substance produced in the developing lungs starting between weeks $21\text{ and }24$ as alveoli begin to form.

Fetal Viability

The developmental milestone reached around weeks $24\text{--}26$ (and weeks $25\text{--}28$ with intensive care) where the fetus can survive outside the womb.

Placenta

An accessory organ that performs endocrine functions (producing hCG, estrogen, and progesterone), enables nutrient and gas exchange, and provides a protective barrier against certain infections.

Ductus Arteriosus

A specialized vascular structure in fetal circulation that bypasses the fetal lungs because oxygen is supplied by the placenta.

Foramen Ovale

An opening in the fetal heart that acts as a circulatory bypass for the non-functional lungs during intrauterine life.