Basic Embryology

Question 1

What is the difference between prenatal, fetal, and gestational ages?

Answer 1

Prenatal refers to before birth, fetal age is from conception to birth (38 weeks), and gestational age is measured from the last menstrual period (40 weeks).

Question 2

What are the key events in the embryonic period?

Answer 2

The first 8 weeks where all major organs are formed.

Question 3

What are the key events in the fetal period?

Answer 3

The remaining 30 weeks where organs grow larger and become more complex.

Question 4

What occurs during ovulation and fertilization?

Answer 4

The egg is released into the peritoneal cavity, and fertilization occurs in the fallopian tube when maternal and paternal genetic material join to form a zygote.

Question 5

What are cleavage stages such as morula, blastomere, and blastocyst?

Answer 5

Cleavage is the process where the zygote divides, forming blastomeres, then a morula (12-16 cells), and later a blastocyst.

Question 6

What are the functions of the inner cell mass and trophoblast?

Answer 6

The inner cell mass forms the embryo, while the trophoblast forms the placenta.

Question 7

What is the difference between bilaminar and trilaminar embryonic discs?

Answer 7

Bilaminar consists of epiblast and hypoblast layers, while trilaminar includes three primary germ layers: ectoderm, mesoderm, and endoderm.

Question 8

What are the three germ layers and their significance?

Answer 8

Ectoderm, mesoderm, and endoderm are the primary germ layers from which all body tissues develop.

Question 9

What is gastrulation and its importance?

Answer 9

Gastrulation is the process where the epiblast cells invaginate to form the three germ layers.

Question 10

What role does the notochord play in neurulation?

Answer 10

The notochord signals the ectoderm to begin forming the neural plate, leading to the development of the brain and spinal cord.

Question 11

What are the stages of neurulation?

Answer 11

Neural plate forms the neural groove, which eventually becomes the neural tube.

Question 12

Why is folic acid important for neural tube closure?

Answer 12

Folic acid is crucial in preventing neural tube defects by ensuring proper closure of the neural tube.

Question 13

What are somites, intermediate mesoderm, and lateral plate mesoderm?

Answer 13

They are regions of the mesoderm that differentiate to form structures like muscles, urogenital systems, and serous cavities.

Question 14

What are the derivatives of mesodermal divisions?

Answer 14

Somatic mesoderm forms the body wall, and splanchnic mesoderm forms internal organs.

Question 15

What is embryo folding, and when does it occur?

Answer 15

Embryo folding begins at week 4, leading to the cylindrical body plan.

Question 16

What are the major events by the end of week 4 and week 8 in embryonic development?

Answer 16

By week 4, the embryo begins to fold, and by week 8, all major organs are in rudimentary form.

Question 17

When does the heart start pumping in embryonic development?

Answer 17

The heart starts pumping around day 29, which is approximately 4 weeks into development.

Question 18

Why is drug avoidance important during early pregnancy?

Answer 18

Drugs can cause birth defects during the critical period when major organs are forming.

Question 19

What is the difference between monozygotic and dizygotic twins?

Answer 19

Monozygotic twins come from one zygote that splits, while dizygotic twins come from two separate eggs fertilized by two sperm.

Question 20

What is the significance of neural crest cells?

Answer 20

Neural crest cells give rise to sensory nerve cells and other structures in the peripheral nervous system.

Question 21

What is the primitive streak and its role?

Answer 21

The primitive streak is a structure that forms on the surface of the epiblast and is crucial for gastrulation.

Question 22

What is the importance of the amniotic and yolk sacs?

Answer 22

The amniotic sac provides a protective environment for the embryo, and the yolk sac supports nutrient supply during early development.

Question 23

What are the serous cavities, and how do they form?

Answer 23

Serous cavities like peritoneal, pericardial, and pleural cavities form from the lateral plate mesoderm.

Question 24

What structures form from the lateral plate mesoderm?

Answer 24

The lateral plate mesoderm splits into somatic (parietal) mesoderm and splanchnic (visceral) mesoderm, forming the serous membranes around organs.