ORTHO-LEC-2ND-QUIZ (1) PDF - Embryology Questions

PRE-NATAL GROWTH AND DEVELOPMENT TWO-LAYERED EMBRYO (BILAMINAR DISC) 3 PHASES OF PRENATAL DEVELOPMENT 1st Phase - Embryonic Stage 2nd Phase - Embryonic Stage 3rd Phase - Fetal Stage The cell of...

PRE-NATAL GROWTH AND DEVELOPMENT TWO-LAYERED EMBRYO (BILAMINAR DISC) 3 PHASES OF PRENATAL DEVELOPMENT 1st Phase - Embryonic Stage 2nd Phase - Embryonic Stage 3rd Phase - Fetal Stage The cell of outer cell mass that forms the trophoblast while the inner cell mass will form the embryo itself so this time we will have a two layered embryo This two layered embryo is also called as bilaminar disc Layers of bilaminar disc: Epiblast and hypoblast- that’s why its called bilaminar disc since its a bi layer THREE-LAYERED EMBRYO (TRILAMINAR DISC) GENERAL EMBRYOLOGY FERTILIZATION fusion of male and female germ cells to form zygote Spermatozoa - male Ova - female FERTILIZATION TO DAY 4 Through the process of gastrulation we will have a 3rd germ layer this occurs during the 3rd week the 3rd germ layer is the mesoderm and this is form as the process called gastrulation Trilaminar disc its also called 3 layer embryo pag meron Once blastocyst has start approximately five to 6 days to ng germ layer fertilization it brings out of its protective covering and begins the process of implantation in the uterus GASTRULATION Morula is 16 Gastrulation is the process whereby the bilaminar embryonic disc undergoes reorganization to form a trilaminar disc. How the cells of the epiblast migrate to the primitive streak and how the mesoderm will be developed is called the process gastrulation. NEURULATION Neurulation marks the beginning of the formation of the central nervous system and is the process whereby the neural plate forms into a neural tube. The first event in neurulation is the formation of neural plate then grows to cranial to caudal direction The cranial end of the neural plate indicates the future BLASTOCYST brain and the narrow or the caudal end represent the region of spinal cord The resulting folds created at the neural plate is called neural groove Fusion of the neural tube usually begins in the middle of the embryo Once the neural tube has completely fused the process of neuralation is complete FOLDING OF EMBRYO NCC AND HEAD FORMATION rhombomeres - 8 bulges midbrain and rhombomeres 1 and 2 ➔ CF development first stream - face second stream - jaws rhombomeres 3 and beyond ➔ pharyngeal structures Somite formation begins as paraxial mesoderm cells become organized into whorls of cells called somitomeres. The somitomeres become compacted and bound together by an epithelium, and eventually separate NEURAL CREST CELLS from the presomitic neural crest is a collection of multipotent stem cells paraxial mesoderm to located at the side of neural tube form individual somites. NCCs migrate throughout the embryo using a variety of mechanisms and give rise to a large range of cell types receive inductive signals to undergo epithelial- mesenchymal transformation Neural crest helps in the formation of peripheral nervous system So from the folding embryo from a flat disc is converted Homeobox transcription into a 3 dimensional body factor genes Otx2, Msx, Dlx, Barx MIGRATION OF NCC BRANCHIAL ARCHES NCC from forebrain PRIMITIVE MOUTH midbrain hindbrain stomatodeum to form viscerocranium (face) boundaries Ncc give rise to large range of cell type and travel to ear buccopharyngeal towards to face membrane- structure that rupture so that we have DEFECTS DUE TO DEFICIENT CNCC MIGRATION separation of foregu Mandibulofacial Dysostosis (Treacher Collins syndrome) PHARYNGEAL ARCHES or branchial arches vertical grooves pharyngeal pouches pharyngeal clefts mandibular arch- arises from 1st brachial arch Other Conditions: hyoid arch- arises from Pierre Robin sequence second brachial arch Cleft palate Craniosynostosis  MUSCLE DEVELOPMENT di mo mabasa? muscle cells in the first arch check mo nalang sa ppt bes apparent at 5th wk. spread within the first arch into each muscle site origin at 6th- 7th wk. muscle mass of first arch →muscles of mastication muscles of second arch grow upward → muscles of face muscles of 2nd arch PHARYNGEAL ARCHES AND POUCHES muscles of facial expressio first pharyngeal groove - external auditory canal first pharyngeal pouch - middle ear and eustachian tube 2nd and 5th grow over the other arches muscles of 2nd arch muscles of facial expression 2nd pharyngeal pouch - palatine tonsils 3rd pharyngeal pouch - inferior parathyroids and thymus 4th pharyngeal pouch - superior parathyroids 5th pharyngeal pouch - ultimobranchial ody muscles of mastication masseter The brachial arches are separated by what we call brachial medial pterygoid grooves but internally or inside it is separated by lateral pterygoid pharyngeal pouches. temporalis VASCULAR DEVELOPMENT The muscle of the mandibular arch that remain in the first arch and easily would be recognize as muscles of mastication now muscles of the second arch will go upward and become the muscle of the face aortic arch vessels have Muscles of mastication all relate to the mandible and passed through the masticatory muscle of mandibular arch medial pterygoid pharyngeal arch tissue then disappear (4 wks.) NEURAL DEVELOPEMENT 3rd pharyngeal arch vessels become the right and left common carotid that nerves develop in supplies the face (via conjunction with the internal carotid and developing muscle fibers stapedial arteries (5 wks.) nerve V grows into the 1st arch nerve VII into the 2nd arch nerves V, IX, X contribute to tongue muscles  INNERVATION AND VASCULARIZATION OF PHARYNGEAL ARCHES Reichert cartilage (2nd arch) - stapes, styloid process, lesser horn, upper body of hyoid 3rd arch cartilage - greater horn, lower part of hyoid body 4th arch cartilage - hyoid cartilage The nerve of the first brachial arch is 5th cranial trigeminal 5th arch cartilage - no nerve for the innervation of muscles of mastication derivatives For second brachial arch is facial nerve for facial muscle 6th arch cartilage - 3rd brachial arch is for glossopharyngeal nerve laryngeal cartilage DEVELOPMENT OF CF SKELETON (CARTILAGES) BRANCHIAL ARCHES AND MUSCLES nasal capsule (ethmoid)- Earliest cartilage sphenoid auditory capsule basioccipital cartilage formed as single cartilaginous unit initially then separate later to form CRANIOFACIAL DEVELOPMENT individual bones transformed into bone by CARTILAGINOUS SKELETAL DEVELOPMENT endochondral bone formation Meckel’s cartilage (1st arch) → malleus → incus Meckels cartilage will not become mandible and it becomes part of middle ear All of this cartilage will arise as cartilaginous continuum in Malleus and incus are the midline parts of middle ear Sphenoid cartilage being posterior to the ethmoid and later Meckles cartilage- initial form the wings of the bone laterally Behind sphenoid is site of osteogenesis occipital cartilage Meckels cartilage use in the formation of mandible- DEVELOPMENT OF CF SKELETON (BONES) serves as scaffolding in formation of mandible CRANIAL BONES membrane(flat)bones Board exam question: Where is the location of the site of frontal osteogenesis relative to meckels cartilage? parietal Answer: lateral squamous portion of temporal Board question: is a cartilaginous joint where bones are intraoccipital joined together formed by intramembranous bone formation Answer: hyaline cartilage FACIAL BONES primary TMJ facial bones malleus-incus joint premaxilla functions in jaw maxilla movement during first zygomatic bone 4 mos. prenatal petrous portion of temporal secondary TMJ appear as tiny ossification centers inn the face, condyle-temporal increases in diameter articulation spreads anteriorly, posteriorly and upward occurs pre- and postnatally MAXILLA maxillary bones grow medially into the palate MANDIBLE body grows laterally to Meckel’s cartilage and posteriorly to join the body with cartilaginous condyle body of mandible and cartilaginous condyle replace the Meckel’s cartilage develops as several units: condylar, body, angular process, coronoid process, alveolar process DEVELOPMENT OF CF SKELETON (SUTURES) sutures - fibrous joints in which the opposing surfaces are closely united facial sutures zygomaticomaxillary frontomaxillary zygomaticotemporal syndesmosis - fibrous joint in which 2 adjacent bones are linked by strong membrane or ligaments cranial sutures SUTURES (3 TYPES) 1. simple - uncomplicated band 2. serrated - interdigitating type 3. squamosal - beveled or overlapping synchondrosis is a cartilaginous joint where bones are joined together by hyaline cartilage synchondrosis articulations grow by forming new cartilage in the center of the suture ethmosphenoid sphenoccipital synostosis is a type of suture in which there is bone-to- bone union e.g. midpalatal suture CLINICAL IMPLICATIONS Craniosynostosis is a condition in which the sutures close too early, causing problems with normal brain and skull growth arch expansion and midpalatal suture  DEVELOPMENT OF THE FACE The nostrils deepen as the tissues around them continue to grow anteriorly, and the internasal area, that is the WEEK 4-7 distance between the nostrils, represents the width of the The development of the face is a continuation of prenatal face. developmenT. Then gradually the frontal prominence diminishes and the So at week 4 to week 7, these are the weeks which are face broadens. supposed to be related to the development of the face. The eyes now become prominent on the sides of the head, and throughout the 5th week, the mandibular arch loses the midline constriction. 6TH WEEK broadening of face by lateral growth of brain eyes and maxillary processes at the front mouth slit widens upper lip= MNP+2MaxSeg philtrum = MNP nasal pit, LNP, MNP 4TH WEEK At the 6th week, the lateral parts of the face expand, thereby broadening the face. This is caused by lateral At about 28 weeks of gestation, growth of the brain. we can see there are localized The eyes and the maxillary processes, which were located thickenings that develop within on the sides of the face during the 5th week, now come to the ectoderm of the frontal the front of the face. prominence just above the The mouth slit widens to the point at which the maxillary opening of the stomodeum. and the mandibular tissues merge. These thickenings are known as The nasal processes are limited to the middle of the upper olfactory placodes. lip, which causes the face to appear more human. Then still at 4 weeks, the oral The upper lip is composed of the MNP or the medial nasal pit, is surrounded by several process and the two lateral maxillary segments. masses of tissues. The medial process is now called the philtrum, and the The pharyngeal arches are evident, so we can see there medial process is in close contact with the medial aspect the max mandibular arch and the hyoid arch. of the maxillary process, while the lateral process is above The frontal processes of the brain bulge forward and the maxillary process. laterally to dominate the facial area. Below the frontal processes are two small wedge-shaped border of the lip tissues which are termed as the maxillary processes, and cleft lip = lack of fusion MNP + they lie lateral to the oral pit. MaxP Beneath the maxillary processes is the mandibular arch, nasal fin which appears divided or constricted in the midline. The orbicularis oris heart lies immediately below the face and is one of the The border of the lip consists fastest growing organs. of two maxillary processes During the 4th week, the heart begins to pump blood and the medial third is the throughout the body. medial nasal process. The lack of contact or fusion 5TH WEEK of the medial nasal process nasal placodes and the maxillary processes frontonasal process will result in either a unilateral internasal area or a bilateral cleft lip. The face broadens epithelium coverings of the eyes on the side of head MNP and the maxillary mandibular arch loses midline process normally contact and constriction create a zone of fusion known During the 5th week, we can see as the nasal fin. the bilateral nasal placodes, which are thickened areas of epithelium This epithelial fin is soon penetrated by connected tissue that appear in the upper border of growth which binds together the two maxillary and the the lip. medial parts, nasal parts of the lip. They develop into nostrils as the tissues around these If this penetration will not occur then the lip could pull placodes grow, resulting in two slits opening into the oral apart and soon the orbicularis oris muscle grows around pit. At this point, the frontal area is now known as the the oral pit to provide support to the upper lip. frontonasal process. The nasal pits continue behind the nasal fin to open into the roof of the mouth at six weeks. 7TH WEEK 6.5 WEEKS more human appearance eyes - front, level with nostrils nose less than in 4th wk upper lip, philtrum danger of cleft lip has passed By the seventh week, the face becomes more human. The eyes approach the front of the face and the nose represents The picture is the frontal section of the head of 6.5 weeks the face more than it did during embryo. (image A) the fourth week. We can see the palatal shelf are in a vertical position, located on each side of the tongue. The lateral growth of the brain resulting in facial expansion Image B - ventral view of the palatine shelf after we causes the eyes now to appear on the front of the face removed the lower jaw and the tongue. which makes it more recognizable as human. Note the clefts between the primary triangular palate A third of the face has been added lateral to each nostril and the palatine shelf which are still vertical. and the eyes are on the same level as the nostrils which will change after the bridge of the nose develops and lengthens. 7.5 WEEKS The upper lip has fused producing a medially located philtrum. The mouth is limited in size with a change in the facial proportions and the danger of cleft has already passed. DEVELOPMENT OF THE PALATE Initially, there is a common oral nasal cavity. there is a common oral nasal cavity and you can see that it's bounded anteriorly by the primary palate and this particular cavity now is mainly occupied by the tongue. Now it's only after the development of the secondary IMAGE A - Frontal section of 7.5 week embryo. palate will there be a distinction between the oral and the The palatine shelf have move into a horizontal position. nasal cavity. What happens here is, the tongue moves down so that The palate proper develops from the primary and the is the opportunity for the 2 palatine shelf to assume a secondary components. horizontal position So, if we now take a look at the ventral view of the FORMATION OF SECONDARY PALATE palatine shelf, we can see that the two shelves are now in a horizontal position. IMAGE B So for the closure of the secondary palate, it proceeds gradually starting from primary plate, it goes to posterior direction. PALATE DEVELOPMENT So this is how the positioning of the fetus affects the lowering of the tongue. We can see here the head of the fetus. When the head suddenly uprights in position, that brings about the tongue to move downward thus allowing Now the palate develops from: the two palatine shelves to assume a horizontal position An anterior wedge-shaped medial part called the medial palatine process. Two lateral palatine processes. The medial part is also known as the primary palate because it develops first and it also is a floor to the nasal pits. 10 WEEKS DEVELOPMENT OF THE TONGUE We can see here the two palatine shelf have fused with each other and also with the nasal septum. The tongue begins to develop at four weeks of gestation, and the pharyngeal arches meet in the midline beneath CLOSURE OF PALATAL SHELVES the primitive mouth. Local proliferation of the mesenchyme then gives rise to a number of swellings in the floor of the mouth. So first, we have the swelling called the tuberculum impar. It arises in the middle or in the midline of the mandibular process. Then we have the lateral lingual swellings. We have two of these lateral lingual swellings. They quickly enlarge and merge with each other and that of the tuberculum impar to form a large mass from which the mucous membrane of the anterior two-thirds of the tongue is formed. For the anterior two-thirds, these are the structures that are responsible for its formation. Now for the posterior one-third, which means the root of The horizontal palatine shelves, they contact in the the tongue, it arises from a large midline swelling midline. developed from mesenchyme of the second, third, and It starts from the primary palate then goes posteriorly. fourth brachial arches. Then the initial contact behind the median palatal Here, the swelling consists of the copula and the segment, and then the tissues will now merge anteriorly hypobranchial eminence. As the tongue now develops, the and posteriorly from the initial point of contact. hypo brachial eminence overgrows the copula, which then The first sight of contact is just posterior to the median eventually disappears. The posterior part of the fourth palatine process. arch marks the development for the epiglottis. The final step in fusion is the removal of the midline epithelial barrier between the right and left shelves. 7 weeks - the palatine shelf is in a vertical position 8 weeks - the palatine shelves have elevated, coincidence with the lowering or the depression of the tongue 9 - 10 weeks - final fusion, fusion of palatine shelves with each other, and with the nasal septum