lect 1/2 odontogenic development of maxillo-facial region

What are the three periods of prenatal development in the lecture?

Proliferative (first 2 weeks), embryonic (2nd–8th weeks), and fetal (8th week to birth).

What events occur during the proliferative period?

Fertilization, implantation, and formation of the embryonic disc.

Where does fertilization occur according to the lecture?

In the oviduct.

What is formed when the sperm and egg cell nuclei unite?

A zygote.

How does the lecture describe the ovum?

A large, round cell.

How does the lecture describe the sperm cell?

A small, highly mobile cell.

What is a zygote?

The fertilized egg formed by union of the female gamete (ovum) and male gamete (sperm).

What is the sequence of developmental stages listed after fertilization?

Zygote → morula → blastocyst → gastrulation → neurulation.

What is the morula?

A ball of approximately 10–32 cells formed by rapid cell divisions in the oviduct.

What happens after the first rapid division of the zygote?

Two new cells are formed.

What is the four-cell stage?

A stage reached after the next cell division during early development.

When does the morula begin migrating toward the uterus?

At the end of the first week, according to the lecture.

What happens to the morula as it develops in the uterus?

It increases in size, swells, and becomes a blastocyst.

How does the lecture describe the blastocyst?

An asymmetrical, hollowing ball of cells with a cavity and a small inner cell mass.

What forms as the blastocyst swells?

A cavity develops and a small inner cell mass forms.

How is the embryonic disc formed in the lecture?

Two small cavities develop on either side of the inner cell mass and meet centrally to form a small disc.

What does the embryonic disc develop into?

The embryo, described as being composed of the walls of the two adjacent sacs.

Which cell layer lines one sac associated with the embryonic disc?

Ectodermal cells, which the lecture says form the outer body covering (epithelium).

Which cell layer lines the other sac associated with the embryonic disc?

Endodermal cells.

What is gastrulation?

The process in which a third layer, mesoderm, develops between ectoderm and endoderm.

When does the lecture place gastrulation?

In the second week of embryogenesis.

What is said to happen to the primitive ectoderm toward day 14?

It thickens to form the “primitive plaque.”

What structure forms in the primitive plaque according to the lecture?

The primitive groove.

What forms at the cranial edge of the primitive groove?

The primitive node.

What happens to cells of the primitive groove and node during gastrulation?

They become mitotically active, divide, and penetrate between ectoderm and endoderm to form primitive mesoderm.

How does the lecture describe mesoderm formation?

Ectoderm invaginates beneath the primitive streak; inserted cells divide the ectoderm and endoderm.

Which structures does the lecture list as ectoderm derivatives?

Skin, nails, hair, sweat glands, enamel, and the superficial layer of oral mucosa, among others.

Which structures does the lecture list as mesoderm derivatives?

Muscles, connective tissue, cartilage, and bone.

What does the lecture state about endoderm and oral structures?

It states that endoderm does not participate in forming oral structures.

What is the notochord according to the lecture?

An axial rod of mesoderm formed by cells detaching from the primitive plaque and penetrating deeper.

What does the notochord initiate?

Formation of the neural plate.

How does the neural plate change during neurulation?

It thickens through proliferation, invaginates centrally, and forms the neural groove.

What surrounds the neural groove as it deepens?

Two neural folds.

How is the neural tube formed?

The neural folds deepen and move toward each other until they meet at the midline.

Where is the neural tube located?

Dorsally along the entire length of the embryo.

What structures lie on both sides of the neural tube?

Two neural crests, according to the lecture.

Which embryonic tube part is described as growing fastest and forming the head?

Pars cranialis.

What does pars umbilicalis form according to the lecture?

The torso and its organs.

What does pars caudalis form according to the lecture?

The limbs.

What happens to the embryo’s head during the fourth embryonic week?

It bends anteriorly as it grows, pushing the heart ventrally.

Where does the oral pit develop during the fourth week?

Between the brain and the heart.

What is the primitive oral cavity called?

The stomatodeum (also written “stomadeum” in the lecture).

What separates the stomatodeum from the developing gut?

The buccopharyngeal or oropharyngeal membrane.

How does the lecture describe formation of the stomatodeum?

It forms ventrally through deep ectodermal proliferation that pushes the mesoderm.

What does the lecture say happens where the stomatodeal ectoderm meets endoderm?

The ectoderm merges with the endoderm.

What happens to the oropharyngeal membrane according to the lecture?

The double membrane becomes a monolayer, and its cells disintegrate.

When does the lecture say an opening forms in the oropharyngeal membrane?

At 20–25 days.

How many pairs of pharyngeal arches are listed in the lecture, and what shape are they?

Six pairs, described as U-shaped.

What forms the core of the pharyngeal arches according to the lecture?

Mesenchymal tissue formed by migrating neural crest cells.

How are the pharyngeal arches covered and lined?

They are covered externally by ectoderm and lined internally by endoderm.

What components does each pharyngeal arch have?

Its own cartilage, nerve, vascular, and muscular components.

What do the pharyngeal arches separate according to the lecture?

The stomatodeum from the developing heart.

Why are they called pharyngeal arches?

They bend around the sides of the pharynx as bars of tissue.

What separates adjacent pharyngeal arches?

An ectodermal pharyngeal groove and an endodermal pharyngeal pouch.

What does the first (mandibular) pharyngeal arch give rise to in the lecture?

The maxillary and mandibular processes.

Which structures and nerve does the lecture associate with the second (hyoid) arch?

The hyoid bone, part of the temporal bone, and facial nerve (cranial nerve VII).

Which structures and nerve does the lecture associate with the third pharyngeal arch?

The tongue, hyoid bone, and cranial nerve IX.

Which structures and nerves does the lecture associate with the fourth pharyngeal arch?

The tongue, thyroid cartilage, most laryngeal cartilages, and cranial nerves IX and X.

What does the lecture say happens to the fifth pharyngeal arch?

It becomes incorporated into the fourth arch.

Which structures and nerves does the lecture associate with the sixth pharyngeal arch?

Most laryngeal cartilages, thyroid cartilage, and cranial nerves IX and X.

What happens when tissues of the second and fifth pharyngeal arches overgrow together?

The lecture says arches 2–5 disappear and the neck becomes externally smooth.

During which embryonic weeks does the face form?

Between the fourth and seventh embryonic weeks.

How many facial primordia does the lecture say form the face?

Five facial primordia, which fuse during weeks 5–7.

What are facial primordia described as in the lecture?

Ectodermal swellings or prominences filled with mesodermal and neural crest cells.

Where is the frontonasal prominence located and what does it give rise to?

Above the oral pit; it gives rise to the forehead.

Where do the two mandibular prominences develop from, and what do they form?

They develop from the first pharyngeal arch below the oral pit and give rise to the lower jaw.

Where do the two maxillary prominences develop from, and what do they form?

They develop from the first pharyngeal arch, lie lateral to the oral pit, and give rise to the maxilla.

What appears at the upper border of the lip during the fifth week?

Bilateral nasal placodes.

What is the frontal area called as development proceeds during the fifth week?

The frontonasal process.

What happens to the frontal prominence and face during the fifth week?

The frontal prominence diminishes and the face broadens.

How do the eyes appear during the fifth week according to the lecture?

They become prominent on the sides of the head.

Where do nasal pits develop?

On the sides of the face, according to the lecture.

Which processes are identified in the sixth-week facial development slide?

Medial and lateral nasal processes and maxillary processes.

What fusion is described for the seventh prenatal week?

The medial nasal and maxillary processes have merged.

How does the position of the eyes change by the seventh week according to the lecture?

The eyes are closer to the front of the face.

What does the lecture say about the nose and eyes at the seventh week?

They are on the same horizontal plane, which changes with vertical growth of the face.

What structure separates the oral cavity from the nasal cavity?

The palate.

When do the two mandibular processes meet in the midline?

They meet in the midline around days 30–35 of prenatal development, according to the lecture.

How does the lecture describe the growth direction of the mandibular processes?

They grow forwards and outwards before meeting and fusing in the midline.

How is the lower lip formed embryologically according to the lecture?

By merging of the two streams of ectomesenchyme from the mandibular processes.

Which pharyngeal arch gives rise to the mandibular processes?

The first pharyngeal arch, also called the mandibular arch.

What is Meckel’s cartilage, and which arch forms it?

A cartilage formed from the first pharyngeal arch and associated with mandible formation.

What happens to Meckel’s cartilage during the sixth week?

It forms a rod surrounded by a fibrocellular capsule.

How are the two Meckel’s cartilages positioned at the midline?

According to the lecture, they do not meet at the midline and are separated by a thin line of cartilage called the symphysis.

How does mandibular bone formation begin according to the lecture?

Intramembranous ossification begins in the mesenchyme and spreads anteriorly and posteriorly to form the mandible.

What happens as mandibular ossification spreads anteriorly?

Bone extends to the midline of the developing lower jaw and fuses shortly after birth, according to the lecture.

How does the ramus of the mandible develop according to the lecture?

Through rapid posterior ossification into the mesenchyme of the first pharyngeal arch.

What localized ectodermal thickenings appear in the frontal prominence at about day 28?

Olfactory placodes.

How do the nasal pits form according to the lecture?

Rapid mesenchymal proliferation around the olfactory placodes creates a horseshoe-shaped ridge that converts each placode into a nasal pit.

What are the two arms of the horseshoe-shaped ridge around a nasal placode called?

The lateral arm is the lateral nasal process; the medial arm is the medial nasal process.

Which structures arise from the paired medial nasal processes together with the frontonasal process?

The middle portion of the nose, middle portion of the upper lip, anterior portion of the maxilla, and primary palate.

How is the upper lip formed according to the lecture?

By fusion of the maxillary process on each side with the medial nasal process.

What structures result from merging of the two medial nasal processes?

Part of the upper lip, the part of the maxilla carrying the incisor teeth, and the primary palate.

What groove forms when the maxillary processes fuse with the lateral nasal processes?

The naso-optic groove, extending from the medial corner of the eye to the nasal cavity, as described in the lecture.

What are the main components of palatal development?

Formation of the primary palate, formation of the secondary palate, and fusion of their processes.

During which weeks does the lecture place palatal development?

The lecture describes palatal development from the seventh to the ninth week.

Which facial processes contribute to the palate according to the lecture?

The frontonasal process and the maxillary processes, including an anterior wedge-shaped medial part and two lateral palatine processes.

How does the lecture describe formation of the primary palate?

It attributes primary palate formation to fusion of the medial nasal processes and the medial palatine process originating from the frontonasal process.

What is the primary palate described as in the lecture?

The medial part of the developing palate.

How does the secondary palate form according to the lecture?

From two lateral palatine processes that develop from maxillary tissue, project internally from the maxillary prominences, and grow toward the midline.