Lecture 1: Early Embryology

What are the three phases of prenatal development?

Week 1-4: Cellular proliferation and migration; Week 5-8: Differentiation and morphogenesis; Week 9-40: Growth and maturation.

Why is the embryo particularly vulnerable during weeks 5-8 of prenatal development?

Many congenital defects can arise during this time due to differentiation of major structures.

What does mitosis produce?

Two identical diploid cells.

What is the main purpose of meiosis?

To produce haploid gametes (sperm and ova).

What are the key outcomes of mitosis and meiosis?

Mitosis results in two identical diploid cells; meiosis results in four haploid gametes.

What initiates the zygote formation?

The fusion of male spermatozoa and female ova during fertilization.

What is the term for the early stage of development that follows fertilization?

Zygote.

Which chromosome abnormality is associated with Down syndrome?

Trisomy 21.

What is trisomy?

A chromosomal condition where there are three copies of a chromosome instead of the usual two.

Which congenital defects are common with trisomy 21?

Facial clefts, shortened palate, protruding tongue, delayed eruption of teeth.

What are the major types of genetic inheritance?

Autosomal dominant and autosomal recessive inheritance.

What is an example of an autosomal dominant genetic condition?

Osteogenesis imperfecta.

What is a hallmark of autosomal recessive inheritance?

The affected gene must be inherited from both parents.

What characterizes trisomy 13?

Brain malformations and often a single placental artery.

What process generates the bilaminar embryonic disc?

Differentiation of the embryoblast cells in the blastocyst.

What are the two cell types in the blastocyst?

Trophoblast and embryoblast (inner cell mass).

Which structure is primarily responsible for nutrient/waste exchange during implantation?

Trophoblast.

How does the secondary yolk sac differ from the primary yolk sac?

The secondary yolk sac becomes the primary site for hematopoiesis.

What critical event occurs during gastrulation?

The transformation of a bilaminar disk to a trilaminar disk.

What is the significance of the primitive streak?

It serves as an organizing center for the formation of germ layers.

What happens during the process of convergent extension?

Cells intercalate and move directionally to narrow tissue along one axis and elongate perpendicularly.

What are the components of each somite?

Sclerotome, myotome, and dermatome.

What does the neural tube develop from?

A thickening within the ectodermal layer.

What condition is characterized by incomplete closure of the spinal column?

Spina bifida.

What disorder occurs due to insufficient generation of cranial neural crest cells?

Treacher Collins Syndrome.

What are ectodermal dysplasias?

A group of rare genetic disorders affecting teeth, hair, nails, and sweat glands.

What does the term 'epithelial-mesenchymal transition' (EMT) refer to?

The process where cells lose contacts and become migratory.

What is a major risk during the organ growth phase of development?

Potential congenital defects due to issues in cellular differentiation.

What are some consequences of cell migration during gastrulation?

Formation of the mesoderm and establishment of body axis.

What's the relationship between the ectoderm and the neural crest cells?

Neural crest cells are derived from the ectoderm.

Which signaling pathway regulates proliferation, polarity, and differentiation?

Wnt signaling pathway.

How do BMP signals affect cell behavior?

They influence proliferation, differentiation, cell migration, or apoptosis.

What important genetic signal links to jaw and cheekbone development?

Neural crest cell migration.

What does the term 'developmental biology' encompass?

The study of the processes of embryonic growth and differentiation.

When do the major tissues and organs start differentiating in the embryo?

During the third to fourth week of development.

What structure becomes the floor of the amniotic cavity?

The neural tube.

What critical point do embryonic cells reach during the timeline from fertilization to gastrulation?

The transition from a zygote to a bilaminar disk and then to a trilaminar disk.

What does the term 'sclerotome' refer to?

The component of the somite that contributes to vertebrae and associated structures.

What commonality exists between ectodermal dysplasias?

Mutations in genes like EDA and EDAR related to ectodermal structures.

How do trisomy conditions typically present at birth?

With severe malformations or developmental issues.

Which two structures develop from the ectoderm?

Epidermis and neural crest derivatives.

What two aspects of signals critically affect the responses in cells?

Amplitude and duration of the signal.

Why is the process of fertility crucial for genetic material exchange?

To ensure proper chromosomal number in the zygote.

What does the term 'competence' mean in cellular biology?

The ability of cells to respond to signaling molecules.

What role does the mesoderm play in the developing embryo?

It gives rise to muscles, connective tissue, and internal organs.

At what stage does cleavage occur in early embryology?

Immediately after fertilization.

Which phase involves the distinct separation of the inner cell mass into two layers?

Formation of the bilaminar disk.

How does the trophoblast contribute to early embryonic development?

It aids in implantation and nutrient exchange.

What signifies the beginning of the morula stage?

The formation of a solid ball of cells after cleavage.

How is the secondary yolk sac formed?

Through differentiation and migration of cells from the extraembryonic endoderm.

What is the risk of having an abnormal chromosome number due to meiosis defects?

Potential developmental disorders like trisomy or additional congenital defects.

During which cellular process might genetic diversity be introduced?

During prophase I of meiosis.

What indicates proper development and organization of germ layers in the embryo?

Successful completion of gastrulation.

What is the defining characteristic of primary oocytes?

They are arrested in prophase I until puberty.

What is observed during the migration of neural crest cells?

They become diverse cell types throughout the embryo.

What role does apoptosis play in embryonic development?

It regulates the proper removal of unwanted cells.

What is significant about the ectoderm's development in the early embryo?

It forms the structure for the nervous system and external structures like skin.

What is a key factor in the differentiation of the facial structures?

The activity of the neural crest cells.

What characterizes the notochord, and how does it form?

It is the defining structure that forms from cells migrating through the primitive streak.

What embryonic layer is responsible for developing into the skin and nervous system?

Ectoderm.

What does the presence of somites predict in embryo development?

The segmentation of the trunk and the development of body structures.

What physiological events are crucial for proper face and skull development?

Migration of neural crest cells and their differentiation.

How does the embryonic folding process affect development?

It allows for shaping and organizing the embryo into a more complex structure.

What signifies neural tube closure defects?

Conditions like spina bifida and anencephaly.

How is embryonic cell fate influenced during early development?

Through signaling pathways that direct differentiation.

What role does the primitive streak play in the embryo's development?

It serves as a signaling center guiding germ layer organization.

What are the major contributions of the lateral plate mesoderm?

Development of the circulatory system and body cavities.

What interaction initiates the differentiation of cells during development?

Induction from signaling molecules.

What is the primary function of the endoderm layer?

To create the lining of internal organs and structures.

What abnormality is associated with insufficient neural crest cell development?

Facial and dental malformations.

Define 'morphogen gradient' and its significance in embryonic development.

Spatial distribution of signaling molecules affecting cell fate based on proximity.

How does the blastocyst undergo implantation?

The trophoblast attaches to the uterine wall, enabling nutrient exchange for the embryo.

What occurs during the cleavage stage of development?

Cell division occurs without growth, resulting in smaller blastomeres.

What is meant by the term 'induction' in developmental biology?

The process of initiating cell differentiation.

Why do congenital anomalies often arise during weeks 5-8 of development?

During this time, major organ systems and structures are undergoing critical formation.

What is the development fate of mesodermal cells during gastrulation?

They contribute to the formation of muscles, bones, and the circulatory system.

Which factors influence the migration and final localization of neural crest cells?

Signals from surrounding tissues and extracellular matrix components.

What genetic factors are commonly involved in ectodermal dysplasias?

Mutations affecting ectodermal structure development.

Identify an important organizing center during early development.

The primitive node at the end of the primitive streak.

How is differential cell fate established among embryonic cells?

Through gradients of signaling molecules influencing gene expression.

What is the clinical significance of understanding embryology?

To diagnose and potentially prevent congenital anomalies.

What events characterize the first few weeks post-fertilization?

Rapid cell division, differentiation, and establishment of body axes.

How do somite structures influence embryonic development?

By defining segments along the body axis, contributing to vertebrae and musculature.