Embryology Week 1 & 4 Overview

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Questions and Answers

What are the three tissue layers that arise from the tri-laminar embryonic disc?

Endoderm, notochord, mesoderm

Ectoderm, mesoderm, endoderm (correct)

Mesoderm, ectoderm, endoderm

Ectoderm, endoderm, somatoderm

During which weeks does the early phase of embryogenesis occur?

Week 9-term

Week 1-4 (correct)

Week 2-6

Week 5-8

What is the primary focus of embryogenesis during weeks 5-8?

Formation of the neural crest cells

Development of all key structures of tissues and organs (correct)

Growth of the fetus

Proliferation of embryonic origins

Which process is NOT part of embryogenesis?

Growth maturity Signup and view all the answers

What are derivatives in the context of embryogenesis?

Structures formed from the tissue layers Signup and view all the answers

Which cells are primarily associated with the development of facial structures?

Neural crest cells Signup and view all the answers

What happens during the fetal development phase?

Growth and maturation of the fetus Signup and view all the answers

What describes the blastocyst's role in early embryogenesis?

It implants into the uterine wall Signup and view all the answers

Which cranial nerve is associated with the first pharyngeal arch?

Trigeminal Nerve (V) Signup and view all the answers

Which structure is NOT derived from the second pharyngeal arch?

Cartilage of the larynx Signup and view all the answers

What is the primary function of the muscles derived from the third pharyngeal arch?

Swallowing support Signup and view all the answers

Which of the following statements regarding the nerve supplies of pharyngeal arches is incorrect?

The first arch's nerve is the Glossopharyngeal Nerve. Signup and view all the answers

Which bones form from the first pharyngeal arch?

Mandible and Maxilla Signup and view all the answers

What type of cartilage is associated with the second pharyngeal arch?

Reichert’s cartilage Signup and view all the answers

What component is NOT part of the neural crest cell derivatives in the pharyngeal arches?

Muscle tissue Signup and view all the answers

Which arteries are incorrectly matched with their corresponding pharyngeal arches?

Second arch - 1st aortic arch Signup and view all the answers

What do the cranial and sensory ganglia migrate to form?

Cranial nerves, peripheral nervous system, and teeth Signup and view all the answers

Which structure separates the primitive mouth from the primitive gut in early embryogenesis?

Bucco-pharyngeal membrane Signup and view all the answers

What are the pharyngeal arches also known as?

Branchial arches Signup and view all the answers

Which specialized tissue does NOT form connective tissues in the head, face, and oral cavity?

Enamel Signup and view all the answers

What marks the initial formation of the embryo’s mouth?

Stomodeum Signup and view all the answers

What occurs when the bucco-pharyngeal membrane ruptures?

Communication between the stomodeum and primitive gut Signup and view all the answers

What role do cranial and sensory ganglia play during embryogenesis?

They contribute to the development of facial and oral structures. Signup and view all the answers

Which of the following is NOT considered ectomesenchyme?

Neural tissue Signup and view all the answers

What is the primary structure that fuses to form the primary palate during weeks 6-7 of development?

Medial nasal prominences Signup and view all the answers

During which weeks does the secondary palate develop?

Weeks 7-8 Signup and view all the answers

What initiates the formation of the secondary palate?

Growth of palatine shelves Signup and view all the answers

What anatomical feature forms at the midline between the primary and secondary palates?

Incisive foramen Signup and view all the answers

What is the significance of neural crest cells during early embryogenesis?

They play a crucial role in forming facial structures. Signup and view all the answers

From which arches does the anterior two-thirds of the tongue develop?

1st and 2nd pharyngeal arches Signup and view all the answers

Which developmental anomaly is specifically associated with the improper fusion of the facial structures?

Cleft lip and palate Signup and view all the answers

What is the clinical significance of disrupted development of the tongue?

Tongue tied Signup and view all the answers

Which of the following structures undergoes ossification starting in week 7 of development?

Maxilla and mandible Signup and view all the answers

What are pharyngeal arches responsible for in embryonic development?

They contribute to skeletal and muscular structures in the head and neck. Signup and view all the answers

Cellular apoptosis during tongue development allows for which of the following?

Creation of the frenulum Signup and view all the answers

Which developmental aspect is directly influenced by the embryonic origins during the formation of the face and palate?

Formation of the jaw and teeth Signup and view all the answers

What is one major outcome of improper embryogenesis in the context of fetal development?

Developmental anomalies such as cleft lip and palate Signup and view all the answers

Study Notes

Early Embryogenesis: Week 1

The inner cell mass congregates on one side, forming the embryonic disk and three embryonic layers.
Stem cells migrate throughout the embryo, giving rise to cranial and sensory ganglia, peripheral nerves, and connective tissues in the head, face, and oral cavity.
Ectomesenchyme forms specialized connective tissues in the head, face, and oral cavity, such as dentine, pulp, and cementum, but NOT enamel.

Early Embryogenesis: Week 4

The embryo starts to take shape through folds, forming the stomodeum (primitive mouth) and the bucco-pharyngeal membrane.
The bucco-pharyngeal membrane separates the primitive mouth from the primitive gut.
The bucco-pharyngeal membrane ruptures, allowing communication between the stomodeum and the gut.
Bulges called pharyngeal arches (branchial arches) develop, forming the building blocks for face and oral cavity structures.
Each pharyngeal arch has its own nerve supply, blood supply, and cartilage.

Pharyngeal Arches and Derivatives

Each arch contributes to specific structures:
- 1st Arch (Mandibular): Trigeminal nerve, 1st aortic arch blood vessel, muscles of mastication, Merkel’s cartilage, Mandible, Maxilla, Zygomatic bones, Squamous portion of temporal bone, Malleus and Incus of ear.
- 2nd Arch (Hyoid): Facial nerve, 2nd aortic arch blood vessel, Muscles of facial expression, Reichert’s cartilage, Part of the hyoid bone, Body of hyoid, Styloid process, Stapes.
- 3rd Arch: Glossopharyngeal nerve, 3rd aortic arch blood vessel, Stylopharyngeal muscle, Connective tissue of the thymus, Inferior parathyroid.
- 4th Arch: Superior laryngeal branch of the Vagus nerve, 4th aortic arch blood vessel, Laryngeal muscles, Cartilage of the larynx (Thyroid, corniculate, and cuneiform).

Development of the Face: Week 4-6

The face continues to develop in detail with the fusion of prominences:
- 1x Frontonasal prominence
- 2x Maxillary prominences
- 2x Mandibular prominences

Development of the Primary Palate: Week 6-7

The primary palate forms from the fusion of the frontonasal prominence and the medial nasal prominences.
The developing tongue occupies the space where the secondary palate will form, hence the primary palate forms first due to limited space.

Development of the Secondary Palate: Week 7-8

The palatine shelves develop and grow around the developing tongue.
The palatine shelves fuse together along the midline with the primary palate and the nasal septum as the tongue retracts.
The incisive foramen forms at the midline between the secondary and primary palates.

Development of the Tongue: Week 4-7

The tongue develops from the 1st, 2nd, and 4th pharyngeal arches.
- Anterior 2/3: 2x lateral lingual swellings (1st arch), Tuberculum impar (2nd arch)
- Posterior 1/3: Copula/hypobranchial eminence.
Cellular apoptosis allows the tongue to separate from the floor of the mouth, leaving a frenulum.

Development of the Alveolar Bone: Week 7

The maxilla and mandible jaws undergo ossification, starting in the respective prominences.

Embryonic Origins

Neural crest cells
Pharyngeal arches

Clinical Significance

Developmental anomalies can occur due to disruptions in the developmental processes.
Example: Cleft lip and palate.

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Description

Explore the foundational concepts of early embryogenesis during weeks 1 and 4. Understand the development of the embryonic disk, key structures like the stomodeum, and the formation of the pharyngeal arches. This quiz will test your knowledge on the critical phases of human development.