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Name the 3 embryonic germ layers and state what body tissues each later differentiates into.

Ectoderm: nerve tissue, epith (including oral), tooth enamel, hair follicles, finger nails, cutaneous glands

Endoderm: epith -lining of digestive tract and lining of respiratory tract

Mesoderm: CT (includes tissues with in the layer (dermis)), skeletal tissue (bone, cartilage), circulatory system (heart, blood), lymphatics, urinary system, reproductive organs, dentin, pulp, cementum, PDL, muscle tissue (including cardiac heart)


Discuss the process of initiation of the CNS.

-During the 4th week, formation of the CNS begins. First a set of cells differentiates from the ectoderm = neuroectoderm, thickened central band of cells localized to the neural plate of the embryo. The neural plate eventually folds creating the neural groove, as more folding undergoes the neural tube is formed. This process is called neurulation
-The neural tube forms the spinal cord and other neural tissues of the CNS


Identify the significance of the neural crest cells (what tissues of the head and neck do they form?)

-During closure of the neural tube, 2 peripheral steps of neuroectoderm separate from the tube (still covered in ectoderm) = neural crest cells
-NCCs migrate from crests of the neural folds and then join the mesoderm to form the mesenchyme. These cells contribute to tissues of the face, such as, cartilage, bones, muscles, teeth (not enamel) and ligaments


Describe the formation and location of the stomodeum (the primitive oral cavity).

-At the 4th weeks the stomodeum, the primitive mouth has become the stomodeum. The stomodeum is separated by a membrane known as the oropharyngeal membrane


What is the buccopharyngeal membrane? What is its significance?

Buccopharyngeal membrane also known as the oropharygneal membrane is a temporary membrane consisting of external ectoderm overlying endoderm. This membrane is significant because it separates the stomodeum from the primitive pharynx


What are the branchial arches and which one contributes to the formation of the face and oral cavity? What other significant structures accompanies these arches in the formation of the face?

-1st -> Mand Arch: contributes to mand, most of max, mid and lower parts of the face, max processes which give rise to upper cheeks, sides of upper lip and most of hard palate, also contributes to formation of the ant 2/3 of tongue (also the formation of the face and oral cavity?
-2nd -> Hyoid Arch: form the muscles of the facial expression, some of the hyoid muscles, hyoid bone, parts of the tongue (post 1/3) and other head and neck structures
-3rd Arch: form part of the post 1/3 of the tongue nad greater cornu of hyoid bone, lower part of hyoid bone
-4th Arch: form part of the post 1/3 of the tongue and laryngeal cartilage
-5th and 6th Arch: forms laryngeal cartilage

-Pharyngeal pouches: arches are divided by these pouches (slits), they do give rise to external structures (external auditory meatus, develops from the membrane in the 1st branchial arch, which is derived from the first pouch)


Identify the arch that the max processes is derived from and the briefly describe their development.

-The max processes are derived from the mand arch, which are enlargements that appear on the post ends of the upper surface, which grow upward and medially at the sides of the stomodeum, eventually slowly move towards the midline to join up with the medial nasal processes
-The max process gives rise to upper cheeks and sides of upper lip and most of the palate


What structures are formed from the frontonasal processes?

-The bugles produce from the folding at around week 3-4 are called the forebrain which develops the frontonasal process which give rise to the following strucutres: forehead, nose, philitrum, middle of upper lip, ant 1/3 of hard palate and alveolar bone


Briefly describe the formation of the nose including the nasal pits.

-During week 5, depressions of the future nose openings called olfactory pits (nasal pits) derived from lower frontal processes
-Olfactory pits are areas of specialized thickened ectoderm found at locations of developing organs of special senses, and include eye, ears and nose eventually becoming olfactory tissue
-At week 6th olfactory pits deepen and form an opening into the primitive oral cavity


Describe the medial and lateral nasal processes.

-As olfactory pits begin to deepen the surrounding tissue develops into 2 medial nasal processes and 3 lateral nasal processes
-The lateral nasal processes form the side of the nose
-The medial nasal processes form the bridge of the nose and the central band of the philtrum of the lip


Explain the process of fusion for the formation of the upper lip. Identify the structures that join and the timeline of occurrence. What type of fusion is this referred to as?

This is referred to facial fusion, where at the start of week 6 the upper lips begins formation. This occurs by each max process fuse together with each medial nasal process on both sides of the stomodeum. These are brought together by proliferation of the neural crest cells derived from the mesenchyme


Describe the formation of the primary palate, What are the oral boundaries of this area in adult structure.

-Occurs when 3 separate structures join. The actual fusion of tissues is created through a glue like substance produced by the epith cells of the edges of each fusing process
-Eventually, will form premax part of max and ant hard palate
-Boundaries are the nasal septum and oral cavity proper


Briefly describe the process of palatal formation, including the structures that form the palate and a time line of fusion.

-5 weeks is when the primary palate fusion begins
-The remaining palatal structures develop from surfaces of the max processes inside the primitive oral cavity
-As max processes proliferate, 2 shelf like processes grow, initially, downward and towards the tongue causing it to drop to the FOM and the palatal process flip up to horizontal position
-Final formation occurs at week 14
-Once growing medially theses processes met and fuse with each other, the lower border of the nasal septum fuse with the primary palate (is given rise from the intermaxillary segment)


Discuss the significance of palatal clefts for the client and what considerations should occur for the DH?

-Clefting can occurs at any stage of fusion process and is extent of the cleft depends on lack of fusion (begin at week 7-14)
-Clefting is the most common congenital anomaly, resulting in malformation of the orofacial region
-Clefting can create function problems with eating, speech and respiratory and may be caused by genetics predisposition, syndrome or other


What are epith rests and what could develop from them?

-Epith rests are when there is a fusion of embryonic process, groups of epith cells may be entrapped, which may eventually become a cyst


How does the nasal septum form and from what structures is it derived?

-The nasal septum is a growth from the fused medial nasal processes, that begin in the 9th week and finish development in 12th week
-The tissue type that forms the nasal septum will grow inferiorly and deep to the medial nasal processes and superior to the stomodeum, the vertical septum fuses with the horizontally oriented final palate after it forms


Describe the development of the tongue.

-Beginning at week 4, with in the oral cavity, swelling from the branchial arches begin to form the tongue


What are the swelling associated with the development of the ant 2/3 and the post 1/3 of the tongue?

-The mand arch (1st) has 3 swellings that will form the ant 2/3 of the tongue, these are 2 lateral lingual swelling and the tuberculum imper
-A swelling from arches 2-4, form the post 1/3 of the tongue. This is done by the capula aspect of these arches


What are some deformities that may be associated with the tongues development?

-Ankloglossia: also known as 'tied tongue,' which results from a short attachment of the lingual frenum that extends the tongue to the apex (tight frenum). Which can restrict the tongues movements in varies ways


Breifly explain the origin of the thyroid gland.

-The thyroid glands originates and proliferates from the epith at the foramen cerum (between branchial arches 1 and 2, at the middle of the developing tongue)
-Descending tissues proliferates the resulting gland, remains attached to the tongue by a thryoglossal duct which eventually disappears


Explain the development of the primary germ layers beginning with the development of the primitive streak.

-Primitive streak begins development in the 3rd week
-The primitive streak is a rod shaped thickening on the epiblast layer of the embryonic disc (development in week 2), epiblast cells proliferate and grow downward between hypoblast and epiblast forming a 3rd middle layer called the mesoderm.
-Now the epiblast = ectoderm and hypoblast = endoderm
-3 distinct germ layers known as the trilaminar disc


Describe Rahke's Pouch

-Is an additional ectodermal pouch (by invagination), that gives rise to the anterior lobe of the pituitary gland


What is the deformity Ectodermal Dysplasia?

-Lack of development of the ectodermal tissues
-A group condition in which there is abnormal development of the skin, hair, nail, teeth or sweat glands
-Can vary is severity
-Ex: dental hypodontia


What is the Caudocephalic Folding?

-It begins in approx week 3-4
-It is when a flat embryonic disc becomes a tubular structure, this is due to the embryo folding in 2 plans
-The ectoderm grows faster than the endoderm, causing bulges that form arches in the head and neck region (therefore, differential growth occurs)
-The ectoderm is outside and the endoderm becomes inclosed inside