Head & Neck Anatomy | Embryology &
Pharyngeal Arches | INBDE
Introduction
Welcome to a new series on head and neck
anatomy. In this series, we will cover high yield
facts that appear on various exams, including
the integrated national board dental exam and
the part 1 board exam. We will also reference
other resources for more information. In this
article, we will focus on embryology.
The Germinal Stage
The germinal stage refers to the period from
fertilization to the second week after
fertilization. At fertilization, the sperm and egg
unite to form a diploid cell called a zygote. The
zygote cleaves into a ball of cells called a
morula that eventually develops an inner cavity
called a blastocell, becoming a blastula or a
blastocyst. The blastocyst implants itself into
the uterine wall. At two weeks, the blastula has
two layers: the embryoblast, which becomes
much of the embryo, and the trophoblast, which
forms much of the placenta.
The Bilaminar Disk
At three weeks, the embryo has three layers:
ectoderm, mesoderm, and endoderm. This
period is called the embryonic period. During
this time, organ systems are established. The
ectoderm contributes to the skin, nervous
, system, teeth, and facial skeleton. The surface
ectoderm forms the enamel. The mesoderm
contributes to the body skeleton, muscles, and
connective tissue. The endoderm lines the
hollow organ systems, such as the
gastrointestinal tract.
Gastrulation and Differentiation
Gastrulation refers to the transition from a
single sheet of cells to three distinct germ
layers. The neural crest forms the rest of the
two structures, including tooth development.
The primitive streak and primitive node
separate right from left and mediate the
development process. The ectoderm produces
ectoderm cells, the endoderm produces
endoderm cells, and the mesoderm produces
mesoderm cells. These cells differentiate into
various cell types, contributing to the
development of organ systems.
Conclusion
Embryology is a complex subject, but
understanding it is crucial for dental and
medical exams. We hope this article provided
you with a clear and concise overview of the
early stages of embryonic development.
In week three to four of development, the
ectoderm pinches the endoderm and
internalizes it, forming the gut, forka, midga,
and hindgut. The left-behind portion becomes
the yolk sac. Neurulation occurs in week four,
where the neural plate rolls into a tube, forming
Pharyngeal Arches | INBDE
Introduction
Welcome to a new series on head and neck
anatomy. In this series, we will cover high yield
facts that appear on various exams, including
the integrated national board dental exam and
the part 1 board exam. We will also reference
other resources for more information. In this
article, we will focus on embryology.
The Germinal Stage
The germinal stage refers to the period from
fertilization to the second week after
fertilization. At fertilization, the sperm and egg
unite to form a diploid cell called a zygote. The
zygote cleaves into a ball of cells called a
morula that eventually develops an inner cavity
called a blastocell, becoming a blastula or a
blastocyst. The blastocyst implants itself into
the uterine wall. At two weeks, the blastula has
two layers: the embryoblast, which becomes
much of the embryo, and the trophoblast, which
forms much of the placenta.
The Bilaminar Disk
At three weeks, the embryo has three layers:
ectoderm, mesoderm, and endoderm. This
period is called the embryonic period. During
this time, organ systems are established. The
ectoderm contributes to the skin, nervous
, system, teeth, and facial skeleton. The surface
ectoderm forms the enamel. The mesoderm
contributes to the body skeleton, muscles, and
connective tissue. The endoderm lines the
hollow organ systems, such as the
gastrointestinal tract.
Gastrulation and Differentiation
Gastrulation refers to the transition from a
single sheet of cells to three distinct germ
layers. The neural crest forms the rest of the
two structures, including tooth development.
The primitive streak and primitive node
separate right from left and mediate the
development process. The ectoderm produces
ectoderm cells, the endoderm produces
endoderm cells, and the mesoderm produces
mesoderm cells. These cells differentiate into
various cell types, contributing to the
development of organ systems.
Conclusion
Embryology is a complex subject, but
understanding it is crucial for dental and
medical exams. We hope this article provided
you with a clear and concise overview of the
early stages of embryonic development.
In week three to four of development, the
ectoderm pinches the endoderm and
internalizes it, forming the gut, forka, midga,
and hindgut. The left-behind portion becomes
the yolk sac. Neurulation occurs in week four,
where the neural plate rolls into a tube, forming
