Chapter 24 - Developmental Embryology

Question 1

What is embryology?

Answer 1

The study of development from fertilization to birth.

Question 2

Why is embryology important?

Answer 2

It explains how tissues, organs, and systems form and helps understand congenital defects.

Question 3

What are the key stages of embryonic development?

Answer 3

Fertilization → Cleavage → Blastulation → Gastrulation → Organogenesis → Fetal development.

Question 4

What is prenatal development?

Answer 4

Growth from conception to birth.

Question 5

What is postnatal development?

Answer 5

Growth from birth to adulthood.

Question 6

What is fertilization?

Answer 6

Fusion of sperm and egg to form a zygote.

Question 7

What chromosome number is restored at fertilization?

Answer 7

Diploid (2n), half from sperm and half from egg.

Question 8

Where does fertilization occur?

Answer 8

Ampulla of the fallopian tube.

Question 9

How long is the egg viable?

Answer 9

About 24 hours.

Question 10

How long can sperm survive?

Answer 10

3–5 days.

Question 11

What is capacitation?

Answer 11

Biochemical changes that increase sperm motility and prepare it for fertilization.

Question 12

What is the acrosomal reaction?

Answer 12

Sperm enzymes digest the zona pellucida to enter the egg.

Question 13

What is the cortical reaction?

Answer 13

Hardening of the zona pellucida to prevent polyspermy.

Question 14

What is nuclear fusion (syngamy)?

Answer 14

Fusion of sperm and egg nuclei to form a diploid zygote.

Question 15

What is cleavage?

Answer 15

Rapid mitotic divisions without growth.

Question 16

What cells are formed during cleavage?

Answer 16

Blastomeres.

Question 17

What is a morula?

Answer 17

A solid ball of 16–32 cells.

Question 18

When does cleavage begin?

Answer 18

About 24 hours after fertilization.

Question 19

What are the stages of cleavage?

Answer 19

2-cell → 4-cell → 8-cell → Morula.

Question 20

What is holoblastic cleavage?

Answer 20

Complete division (humans).

Question 21

What is meroblastic cleavage?

Answer 21

Partial division (birds, reptiles, fish).

Question 22

What is blastulation?

Answer 22

Formation of the blastocyst.

Question 23

When does blastulation occur?

Answer 23

Day 4–5 after fertilization.

Question 24

What are the parts of the blastocyst?

Answer 24

Trophoblast, inner cell mass, blastocoel.

Question 25

What does the trophoblast become?

Answer 25

Placenta and chorion.

Question 26

What does the inner cell mass form?

Answer 26

The embryo and amnion.

Question 27

When does implantation occur?

Answer 27

Day 6–7 after fertilization.

Question 28

What happens during implantation?

Answer 28

Blastocyst attaches to the endometrium and begins nutrient exchange.

Question 29

What is gastrulation?

Answer 29

Formation of three germ layers and the body plan.

Question 30

What are the three germ layers?

Answer 30

Ectoderm, mesoderm, endoderm.

Question 31

What does ectoderm form?

Answer 31

Skin, nervous system, hair, nails, sensory organs.

Question 32

What does mesoderm form?

Answer 32

Muscles, bones, heart, kidneys, gonads.

Question 33

What does endoderm form?

Answer 33

Digestive tract, lungs, liver, pancreas, bladder, thyroid.

Question 34

What is the notochord?

Answer 34

A mesodermal rod that induces neural development.

Question 35

What is neurulation?

Answer 35

Formation of the neural tube.

Question 36

What does the neural tube become?

Answer 36

Brain and spinal cord.

Question 37

What do neural crest cells form?

Answer 37

Peripheral nervous system and facial structures.

Question 38

When does neurulation occur?

Answer 38

Around week 3.

Question 39

What is organogenesis?

Answer 39

Germ layers forming organs and systems.

Question 40

When does organogenesis begin?

Answer 40

Around week 3.

Question 41

When does the heart begin beating?

Answer 41

Week 4.

Question 42

What is the critical period?

Answer 42

Weeks 3–8 (highest risk for birth defects).

Question 43

When do limb buds appear?

Answer 43

Weeks 4–5.

Question 44

When do lungs and kidneys begin developing?

Answer 44

Weeks 5–6.

Question 45

When do facial features start forming?

Answer 45

Weeks 6–8.

Question 46

What are extraembryonic structures?

Answer 46

Tissues that support the embryo but don’t become the baby.

Question 47

What is the amnion’s function?

Answer 47

Cushions, protects, allows movement, aids lung development.

Question 48

What is the yolk sac’s role?

Answer 48

Early blood cell and vessel formation.

Question 49

What does the chorion form?

Answer 49

Placenta and nutrient exchange structures.

Question 50

What is the allantois?

Answer 50

Forms blood vessels of the umbilical cord and contributes to the bladder.

Question 51

What forms the placenta?

Answer 51

Fetal chorion + maternal endometrium.

Question 52

What does the placenta do?

Answer 52

Exchanges gases, nutrients, wastes, and secretes hormones.

Question 53

When does fetal development occur?

Answer 53

Week 9 to birth.

Question 54

What happens in the first trimester?

Answer 54

Organogenesis completes; high sensitivity to teratogens.

Question 55

What happens in the second trimester?

Answer 55

Rapid growth and fetal movement felt.

Question 56

What happens in the third trimester?

Answer 56

Weight gain, lung maturity, brain growth, passive immunity.