Stages of Development; Exam 1 Flashcards

What is the Germinal Stage, and when does it occur?

The first stage of prenatal development, occurring from fertilization to 2 weeks.

What happens during the first 24 hours after fertilization?

The zygote (fertilized egg) begins rapid cell division through mitosis.

What is a morula, and when does it form?

A solid ball of cells formed 3-4 days after fertilization as the zygote continues dividing.

At what stage does the blastocyst form, and why is it important?

By 4-5 days after fertilization, the morula becomes a hollow ball of cells (blastocyst), which will implant into the uterine wall.

What happens around Day 6-7 of the Germinal Stage?

Implantation begins, where the blastocyst attaches to the uterine wall.

What major structures begin forming in the Germinal Stage?

The placenta and amniotic sac start developing.

What happens if implantation fails?

The zygote is expelled through menstruation, and pregnancy does not occur.

When does the Embryonic Stage occur?

From week 3 to week 8 after fertilization.

Why is the Embryonic Stage the most critical period for development?

Because all major organs and body systems begin forming, and the embryo is most vulnerable to teratogens (harmful substances).

What is the first major structure to form in the embryo?

The neural tube, which later becomes the brain and spinal cord.

When does the heart begin to beat?

Around week 4 (22 days post-fertilization).

What key developments happen between weeks 3-4?

Neural tube forms, heart develops and beats, Eyes, ears, and limb buds appear, Placenta and umbilical cord form for nutrient exchange.

At what point do arms and legs begin to form?

Around week 5, the limb buds elongate.

What happens by the end of week 6?

Facial features (eyes, nose, mouth) develop, The digestive system starts forming, Brain activity begins.

What key developments occur at week 7?

Fingers and toes begin to form, The lungs start developing, The skeleton begins forming from cartilage.

What is the major milestone by week 8?

All major organs are present in their basic form, Sex organs begin to develop (though gender is not visible yet), The embryo is now called a fetus.

When does the Fetal Stage occur?

From week 9 until birth (40 weeks).

What is the primary focus of the Fetal Stage?

Growth and refinement of all body systems and organs.

What major changes occur in weeks 9-12

Reflexes develop (e.g., sucking, swallowing), Fingers and toes fully form, External genitalia begin to differentiate (sex can be determined by ultrasound at week 12), The fetus can move, but movements are too small for the mother to feel.

During what period does the First Trimester take place?

Weeks 9-12

During what period does the Second Trimester take place?

Weeks 13-26

During what period does the Third Trimester take place?

Weeks 27-40

What major developments happen between weeks 13-16?

Lanugo (fine hair) covers the body, The baby begins making facial expressions, Skeletal bones harden.

When can the mother first feel the baby move?

Between 16-20 weeks (quickening).

What happens by week 20?

The baby can hear sounds from outside the womb, Sleep-wake cycles begin, Eyebrows and eyelashes form.

What is the “age of viability,” and when does it occur?

Around 23-24 weeks, when a preterm baby has a chance of survival with medical support.

What major developments occur by week 24?

Lungs produce surfactant, which helps with breathing, The baby can respond to light and sound.

What are the key developments in the third trimester?

Rapid brain growth and more complex neural connections, Fat stores develop for insulation and energy, The baby practices breathing movements.

Why is lung development crucial in the third trimester?

Surfactant levels increase, which prevents lung collapse after birth.

What happens between weeks 36-40?

Weight gain continues rapidly, The baby "drops" into the birth canal in preparation for labor, Organs are fully developed, and the baby is ready for birth.

What happens around weeks 32-34?

Bones fully develop, but are still soft, The baby moves into the head-down position for birth.

When does the zygote implant into the uterus?

Around day 6-7 after fertilization.

At what stage does the heart start beating?

Around week 4 in the Embryonic Stage.

At what week does the baby have all major organs formed?

By week 8, at the end of the Embryonic Stage.

At what stage can the sex of the baby be determined via ultrasound?

Around week 12 in the First Trimester of the Fetal Stage.

What is the survival rate for a baby born at 24 weeks?

Around 50-60% with medical intervention.

What is surfactant, and why is it important?

A lung substance that prevents collapse after birth, forming around 24-28 weeks.

Why does a baby move into a head-down position before birth?

To prepare for easier delivery through the birth canal.

What is the first stage of In-Vitro Development?

Germinal Stage (0-2 Weeks)

What is the second stage of In-Vitro Development?

Embryonic Stage (3-8 Weeks)

What is the third stage of In-Vitro Development?

Fetal Stage (9 Weeks - Birth)