INTRODUCTION TO EMBRYOLOGY

What is embryology?

The study of prenatal development from gamete formation through fetal development.

What anatomical plane divides the body into left and right?

Sagittal plane.

What anatomical plane divides the body into anterior and posterior?

Coronal (frontal) plane.

What anatomical plane divides the body into superior and inferior?

Transverse plane.

How many chromosomes are found in normal human somatic cells?

46 (23 pairs).

A zygote is formed by fusion of what two cells?

A haploid sperm and a haploid oocyte.

Is a zygote haploid or diploid?

Diploid (2n).

What is the master gene of embryogenesis?

Sonic Hedgehog (SHH).

SHH is what type of signaling molecule?

Paracrine signaling factor.

SHH is essential for development of which oral structures?

Teeth and taste buds.

Besides teeth, SHH is important for development of what major organ systems?

Heart, vasculature, gut, limbs, lungs, and left-right body axis.

What gene determines testis differentiation?

SRY gene.

Where is the SRY gene located?

Y chromosome.

In embryology, what is induction?

One group of cells signals another group of cells to differentiate.

What is competence?

The ability of a cell to respond to an inductive signal.

What are the major differences between oogenesis and spermatogenesis?

Oogenesis begins before birth and produces one ovum; spermatogenesis begins at puberty and produces four sperm.

Which process begins during fetal life?

Oogenesis.

Which process begins at puberty?

Spermatogenesis.

How many mature gametes are produced from one primary oocyte?

One.

How many mature sperm are produced from one primary spermatocyte?

Four.

During which process are polar bodies produced?

Oogenesis.

Primary oocytes arrest during which stage?

Prophase I.

Secondary oocytes arrest during which stage?

Metaphase II.

Which hormones stimulate maturation of ovarian follicles?

FSH and LH.

What is the function of the corpus luteum?

Secretes hormones to prepare the uterine endometrium for pregnancy.

What does the corpus luteum become if fertilization does not occur?

Corpus albicans.

What is the function of Sertoli cells?

Support and nourish developing sperm.

What is the developmental sequence during Week 1?

Zygote → Morula → Blastocyst.

Approximately when does the morula form?

Day 3.

How many cells are present in a morula?

Approximately 16 cells.

Approximately when does the blastocyst form?

Day 5–6.

What cavity characterizes a blastocyst?

Blastocoele.

What does the embryoblast become?

The embryo.

What does the trophoblast become?

The fetal portion of the placenta.

What type of stem cells are found in the embryoblast?

Pluripotent stem cells.

Why is Week 2 called the "Week of Twos"?

Formation of two germ layers, two trophoblast layers, and two cavities.

What two layers form the bilaminar disc?

Epiblast and hypoblast.

Which bilaminar layer is dorsal?

Epiblast.

Which bilaminar layer is ventral?

Hypoblast.

What two cavities form during Week 2?

Amniotic cavity and primitive yolk sac.

What are the functions of the primitive yolk sac?

Early nutrition, gas exchange, and hematopoiesis.

Into what two layers does the trophoblast divide?

Cytotrophoblast and syncytiotrophoblast.

Which trophoblast layer is the outer invasive layer?

Syncytiotrophoblast.

What are the three major events of Week 3?

Gastrulation, notochord formation, and neurulation.

Gastrulation transforms what into what?

Bilaminar disc → trilaminar disc.

What are the three germ layers?

Ectoderm, mesoderm, endoderm.

Which germ layer forms the CNS, PNS, epidermis, and enamel?

Ectoderm.

Which germ layer forms muscle, bone, cartilage, heart, and connective tissue?

Mesoderm.

Which germ layer forms the epithelial lining of the GI and respiratory tracts?

Endoderm.

What is the function of the notochord?

Establishes the midline, induces neurulation, and forms the basis of the axial skeleton.

Neurulation is guided by what structure?

Notochord.

What does the neural tube become?

Brain and spinal cord.

What develops simultaneously with neurulation?

Gut tube formation.

The gut tube is divided into what three regions?

Foregut, midgut, and hindgut.

Neural crest cells originate from what embryonic structure?

Neural tube.

Cranial neural crest cells give rise to what?

Facial cartilage, bone, connective tissue, and cranial ganglia.

Cardiac neural crest cells form what?

Outflow tract septum and walls of the great arteries.

Trunk neural crest cells form what?

Melanocytes, adrenal medulla, sympathetic ganglia, and dorsal root ganglia.

Vagal and sacral neural crest cells form what?

Parasympathetic enteric ganglia.

Approximately what proportion of birth defects involve neural crest cells?

About one-third.

When does the fetal period begin?

Week 9.

What major event occurs during the 3rd month?

Face becomes recognizable and primary ossification centers appear.

By what month can fetal sex usually be determined by ultrasound?

Third month.

During which month does the mother usually begin feeling fetal movement?

Fifth month.

What is lanugo?

Fine fetal hair covering the body.

Approximately how much amniotic fluid does the fetus swallow each day during the 4th–5th months?

About 400 mL/day.

What are CRL and CHL used to measure?

Fetal length.

What is the critical period for major structural birth defects?

Fertilization through Week 8 (organogenesis).

Too much or too little amniotic fluid is associated with what?

Birth defects.

What vitamin significantly reduces neural tube defects?

Folic acid (folate).

When should folic acid supplementation ideally begin?

About 3 months before pregnancy.

What are the two main routine prenatal screening tests?

Ultrasound and maternal serum testing.

What does elevated maternal AFP suggest?

Neural tube defects.

At what gestational age does AFP peak?

About 14 weeks.

What is amniocentesis?

Withdrawal of amniotic fluid for diagnostic testing (≥14 weeks).

What is chorionic villus sampling (CVS)?

Sampling placental tissue for prenatal diagnosis.

What does a karyotype detect?

Aneuploidy (extra or missing chromosomes).

What does FISH detect?

Specific chromosomal abnormalities using fluorescent DNA probes.

What does exome sequencing analyze?

The protein-coding regions (exons) of DNA.

What are DNA microarrays used to detect?

Specific gene mutations.

What are the three types of spina bifida?

Occulta, meningocele, and myelomeningocele.

Which type of spina bifida is associated with a hair tuft or dimple?

Spina bifida occulta.

Which type of spina bifida involves protrusion of the meninges only?

Meningocele.

Which type of spina bifida involves protrusion of the spinal cord?

Myelomeningocele.

What is the Pierre Robin sequence triad?

Micrognathia, glossoptosis, and cleft palate.

Which abnormality occurs first in Pierre Robin sequence?

Mandibular micrognathia.

What is glossoptosis?

Posterior displacement of the tongue that obstructs the airway.

What is the most common tumor of infancy?

Hemangioma.

Hemangiomas are composed of what?

Dense collections of capillary blood vessels.

Where are infantile hemangiomas commonly found?

Craniofacial region.