Embryonic Development of the Skeletal System PDF

OUTLINE I. DEVELOPMENT OF THE SKELETAL SYSTEM A. 3rd Week B. End of 3rd Week C. End of 4th Week II. HISTOGENESIS OF CARTILAGE A. 5th Week B. Classification of Cartilage III. H...

OUTLINE I. DEVELOPMENT OF THE SKELETAL SYSTEM A. 3rd Week B. End of 3rd Week C. End of 4th Week II. HISTOGENESIS OF CARTILAGE A. 5th Week B. Classification of Cartilage III. HISTOGENESIS OF BONES Figure 2. (C). Transverse section of an embryo (22 days) shows the appearance A. Long bones of early somites. (D). Transverse section of an embryo (24 days) shows folding of B. Endochondral Ossification the embryo in the horizontal plane (arrows). The dermomyotome region of the C. Intraembryonic Mesoderm somite gives rise to the dermatome and myotome D. Somites IV. DEVELOPMENT OF THE AXIAL SKELETON The paraxial mesoderm further divides to somites. And the somites will divide A. Vertebral Column again to form the sclerotome, dermatome and myotome. B. Ribs C. Sternum C. End of 4th week D. Skull sclerotome cells from mesenchyme (mesenchyme are connective V. FORMATION OF LIMBS tissues capable of forming bones) VI. JOINTS bones appear as condensations (packing up) of mesenchymal cells I. DEVELOPMENT OF THE SKELETAL SYSTEM A. 3rd week Notochord and neural tube formation Intraembryonic mesoderm lateral (to the tube) to these structures thickens (and divide) to form (somites) or the paraxial mesoderm (most radial part is the paraxial then intermediate and lateral mesoderm) B. End of 3rd week Dorsolateral columns become segmented and it’s now called somites Somites will differentiate into two parts: 1. Sclerotome ventromedial part it will form the vertebrae and ribs Mesenchyme transforms into cartilages, and through endochondral formation, 2. Dermomyotome it will become ossified bone. A bone is destined to become a bone by two dorsolateral part processes: the intramembranous ossification or bone formation and myotome part forms myoblasts (primordial muscle endochondral bone formation, the former will the mesenchyme form into bone cells) straight while in the endochondral ossification, the mesenchyme will first form dermatome region forms fibroblasts (dermis)(further into cartilage and then cartilage to bone. develop to skin) Condensation (dense packing): start of selective gene activity, which precedes Formation and Early Differentiation of Somites cell differentiation Mesenchyme: embryonic connective tissue that has bone-forming capacity. Membranous (intramembranous) bone formation: type of osteogenesis wherein most flat bones develop in mesenchyme within pre-existing membranous sheaths. Endogenous Regulators of Chondrogenesis and Skeletal Development 1. CHON (protein) encoded by HOX genes 2. Bone Morphogenic CHON (BMP5, BMP7) 3. GF GDF5 4. Transforming GF-β (TGF-β) super family 5. other signaling molecules Figure 1. (A). Dorsal view of an embryo (18 days). (B). Transverse section of the embryo shown in A shows the paraxial mesoderm from which the somites are β- Catenin: determines the lineage commitment of skeletal precursor cells to derived chondrocytes and osteoblasts. This is the notochord. The blue one is the ectoderm, the red one is the mesoderm, the innermost is the endoderm and the most medial one, the paraxial mesoderm. Page 1 of 9 [EMBRYOLOGY] 1.10 EMBRYONIC DEVELOPMENT OF THE SKELETAL SYSTEM – Dr. Steve S. Arellano, MD II. HISTOGENESIS OF CARTILAGE A. 5th week cartilage develops from mesenchyme mesenchyme condensed to form chondrification centers. Figure 4. External ear Figure 5. Intervertebral discs (IVD) In the 5th week, the cartilage develops from this mesenchyme and endochondral ossification from chondrification centers will become pre-chondrocytes. III. HISTOGENESIS OF BONES This will give rise to chondroblasts or baby cartilages that are capable of secreting ground substance to cellular matrix capable of Bone composition: sustaining in the production further of bones and also collagenous a. Cells fibrils that will give elastic fibers. b. Matrix - (inner part of the bone) organic intercellular These fibers will be deposited in the intercellular matrix. substance (collagen fibrils) B. Classification of Cartilage (according to type of matrix) Osteogenesis and chondrogenesis 1. Hyaline cartilage ○ programmed early in development ○ most widely distributed type ○ independent events influenced by vascular changes ○ ex. joints 2. Fibrocartilage Bone develops from two types of connective tissues: ○ ex. intervertebral discs (IVD) 1. Mesenchyme (intramembranous membrane) 3. Elastic cartilage ○ Intramembranous ossification ○ ex. auricles of the external ears ○ occurs in mesenchyme ○ produces osseous tissue without prior cartilage formation ○ mesenchyme condenses and becomes highly vascular (this is a straight process, it will not turn into cartilage) ○ Process: Osteoblasts lay down lamellae, forming plates of compact bone between the surface plates Intervening bone remains spongy Spongy environment is accentuated by osteoclasts that reabsorb bone In the interstices of spongy bone, the mesenchyme differentiates into BONE MARROW Figure 3. Anterior view of the knee *Osteoclasts: multinucleated cells with a hematopoietic origin. *Hormones and cytokines regulate remodeling of bone by the coordinated action of osteoclasts and osteoblasts Page 2 of 9 [EMBRYOLOGY] 1.10 EMBRYONIC DEVELOPMENT OF THE SKELETAL SYSTEM – Dr. Steve S. Arellano, MD Precursor cells differentiate into osteoblasts (bone-forming cells) and begin to deposit unmineralized matrix called osteoid Wnt signaling is a key factor in osteoblast differentiation Figure 7. Layers of a bone Calcium phosphate is then deposited in osteoid tissue as it is organized into bone The matrix is produced by the chondroblasts Bone osteoblasts are trapped in the matrix and become osteocytes (immature chondrocytes) (cells that are capable of forming bones) Chondroblasts that exists in the perichondrium don’t have a lacunae 2. Cartilaginous Bone Formation The surfaces of most of the cartilage in your body is endochondral in pre-existing cartilaginous models surrounded by a membrane of dense irregular connective tissue called perichondrium (becomes periosteum in A. LONG BONES time) Center of ossification: Diaphysis Chondrocytes that are outside of the perichondrium are chondrocytes hypertrophied surrounded by a space called lacuna (lacunae for plural). matrix become calcified cells divide concurrently Lengthening of Long Bones thin layer of bone is deposited under the perichondrium occurs at the diaphyseal-epiphyseal junction PERICHONDRIUM becomes PERIOSTEUM depends on the epiphyseal cartilage plates (growth vascular connective tissue invade and breaks up the cartilage plates) Osteoblasts reach the developing bone from these blood vessels at the diaphysis, cartilage cells hypertrophy and the matrix becomes calcified. Resorption of Bone keeps the spongy bone masses constant in length and enlarges the medullary cavity. Figure 6. Parts of a long bone showing the epiphysis and diaphysis Figure 8. Adult and child long bone Epiphyseal line - growth plate ○ invading cells form into hematopoietic cells (blood cells of bone marrow) ○ process continues toward the epiphyses ○ spicules of bone remodeled by osteoclasts and osteoblasts ○ transcription factor SOX9 and the co-activator associated arginine methyltransferase 1 (CARM1) regulate osteochondral ossification. Figure 9. Parts of a growing bone Page 3 of 9 [EMBRYOLOGY] 1.10 EMBRYONIC DEVELOPMENT OF THE SKELETAL SYSTEM – Dr. Steve S. Arellano, MD B. ENDOCHONDRAL OSSIFICATION A. cartilaginous bone B. Membranous bone End of Embryonic Period C. Membrano-cartilaginous bone 56 days after fertilization 5. Bones of the axial skeleton are derived from sclerotomes and head start of ossification of limb bones mesoderm time it demands on maternal supply of Ca+ and phosphorus 6. Bones of the shoulder, hip girdle and limbs arise from the lateral pregnant women are advised to maintain an adequate intake of plate mesoderm (extreme mesoderm) these elements to preserve healthy bones and teeth. 7. Some bones of the face and skull are derivatives of the pharyngeal arch’s mesoderm. At Birth diaphyses are largely ossified D. SOMITES epiphyses are still cartilaginous secondary ossification centers appear in the epiphyses 4TH WEEK (somite week or somite period) during the first few years of birth. Somites appear between the 20th and 30th day of development epiphyseal cells cartilage hypertrophies. Somite period development vascular connective tissue invasion is evident ossification spreads radially Divisions of a Somite: articular cartilage & epiphyseal cartilage plate remain cartilaginous 1. Sclerotome ventromedial part On completion of growth cells migrate medially cartilage plate is replaced by a spongy bone surround the neural tube epiphysis and diaphysis are united and fused Give rise to the vertebral column and ribs by age 20 years, NO further elongation of the bone occurs 2. Dermatome Lateral part Growth in diameter of a bone Cells migrate and line the deep surface of the ectoderm results from the deposition of bone at the periosteum and from covering the entire body resorption on the internal medullary surface. Cells give rise to the dermis of the skin and to the rate of deposition and resorption regulates the thickness of the subcutaneous tissue. compact bone and the size of the medullary cavity. internal reorganization of bone continues throughout life C. INTRAEMBRYONIC MESODERM Divisions of the intraembryonic mesoderm 1. Paraxial plates - longitudinal columns on either sides of the notochord and neural tube. ○ Otic Capsules ○ neuroectodermal thickenings ○ forms the membranous labyrinth of internal ear ○ divide the paraxial mesoderm into: - preotic part- unsegmented head mesoderm (somitomeres) Figure 11. End of week 4. Embryo undercutting is complete. Somites have - postotic part- segmented (40-45 pairs of subdivided into sclerotome, myotome, and dermatome, which form the segments or somites) vertebrae, skeletal muscles, and dermis respectively. Body coelom present. 3. Myotome Intermediate part Gives rise to the striated muscles Dermis on the back of the head and trunk is derived from dermatome Dermis elsewhere is derived from lateral plate mesoderm Cervical, thoracic, lumbar and sacral regions, one spinal nerve innervates each myotome; somites form these regions, corresponding to the number of spinal nerves. Coccygeal region, somites exceed the number of spinal nerves but many of them eventually degenerate. IV. DEVELOPMENT OF THE AXIAL SKELETON Figure 10. Embryonic Mesoderm Axial Skeleton composition: 1. Vertebral column SOME GENERALIZATIONS 2. Ribs 1. Skeletal system includes cartilage and bone. 3. Sternum 2. Skeleton is classified into axial skeleton and appendicular skeleton 4. Skull ○ axial composed of skull, vertebrae, ribs. sternum 3. All bones are of mesodermal origin from paraxial mesoderm In general, the skeletal system develops from paraxial, lateral plate (parietal 4. Classification of bones according to mode of ossification layer) mesoderm and from the neural crest. Page 4 of 9 [EMBRYOLOGY] 1.10 EMBRYONIC DEVELOPMENT OF THE SKELETAL SYSTEM – Dr. Steve S. Arellano, MD Can be visualized via UTZ in fetus Amniotic fluid exam: increased alpha- ○ fetoproteins Supposedly they will meet in the middle ○ and form an elevation to become the ○ vertebral spine 2. Meningocoele/ meningomyelocele Gap between neural arches may be large enough for meninges and neural elements to bulge out of it. it can be a meninges, hair, CSF that leaks the hole 3. Hemivertebra Hemi= half; one side Vertebral body ossify from two primary ○ centers which soon fuse One of these parts may fail to develop ○ resulting in only half of the body being present Associated with the absence of the corresponding rib Figure 12. Axial skeleton 4. Anterior spina bifida Two halves of the vertebral body formed naturally but fail A. Vertebral Column to fuse Formed from the sclerotomes Vertebral body then consists of two hemivertebrae Sclerotome cells are converted into loose mesenchyme 5. Klippel-Feil Syndrome Mesenchyme migrates medially & surrounds the notochord Two or more vertebrae that are normally separate may Mesenchyme extends backward & surrounds the neural tube fuse together Such fusion occur in the cervical region (Neck) Extensions of this mesenchyme: One or two vertebrae will fuse place laterally to become the transverse process Hard time moving neck because it is the most mobile part place ventrally in the body wall to become the ribs of the vertebrae, followed by lumbosacral, then thoracic Not snappy enough to move to sides because those bones INTERVERTEBRAL DISC (IVD): developed from a condensed region called are fused perichordal disc 6. Chondro-Osteodystrophy Other structures formed similar to the IVD: (While IVD is developing Ossification of the vertebral body is defective, reducing other structures, it is also forming:) the total length of the spine. Interspinous ligaments Softening of the vertebral body or maldevelopment, Transverse ligaments reducing the numbers or the length of the spine short stature or short body BODY OF VERTEBRA: formed by fusion of the more condensed part of one can lead to the formation of the dwarfs who have short segment with the less condensed part of the adjoining segment. trunks but limbs of normal length. Other structures formed similar to the body of vertebra: ○ Neural arch B. The Ribs ○ Transverse processes Derived from the ventral extensions of the sclerotome mesenchyme ○ Costal element that forms the vertebral arches. Extensions are present in the thoracic, cervical, lumbar and sacral - in the region of the vertebral bodies, the notochord disappears regions. - in the region of the IVD, the notochord becomes expanded and Lie ventrally to the mesenchymal basis of the transverse process with forms the nucleus populous which they are continuous. - nucleus pulposus is the innermost part or center point of IVD; that Thoracic region came as an expansion of notochord ○ Extensions undergo chondrification and then ossification to form the ribs GENERALIZATIONS ○ Some mesenchyme do not undergo chondrification, a. Vertebra, transverse process, and ribs are intersegmental structures rather become loose and form costo-transverse joints formed from portions of two somites Cervical, lumbar, and sacral regions: b. IVD formed at the center of somite ○ Chondrification and ossification of costal arches are c. Spinal nerves are segmental structures that emerged between the confined to the region immediately to the transverse two adjacent vertebrae and lie between two adjacent ribs process. d. Blood vessels supplying structures derived from the myotome(intercostal vessels) C. Sternum 2 sternum: the left and right column CONGENITAL ANOMALIES VERTEBRAL COLUMN During development, these 2 will fuse on midline and ossify because some parts are still cartilage like the xiphoid process- which is still 1. Spina bifida cartilage until adulthood Spina = spine The fusion of two sternal bars will go midline and fuse and condense Bi= two further. Then it will develop the manubrium, the body, and the two spines xiphoid. Two halves of neural arch may fail to Develops from the fusion of the two sternal bars (primordial sternum ○ fuse in the midline or sternal bars) that form in the ventral body wall independent of the Spine did not meet halfway. It looks like it is missing but ribs and clavicle actually there is arrest of fusion of these neural arches. 7th week: Mesenchymal condensation becomes cartilaginous Page 5 of 9 [EMBRYOLOGY] 1.10 EMBRYONIC DEVELOPMENT OF THE SKELETAL SYSTEM – Dr. Steve S. Arellano, MD 8th to 10th week: Deformity of the chest wall in which the breastbone (sternum) and ○ Sternal base fuse with each other in a cranial caudal ribs are pushed outward or protrude more than usual direction to form the manubrium, body, and xiphoid Develops during a rapid growth spurt, in children and adolescents process (these are the adult forms of sternum). aged 10 and older. ○ Laterally, the sternal bars are continuous with ribs. ○ Manubrium and body of the sternum are ossified separately. ○ Xiphoid process only later in life. Figure 15. Chest Anomaly: Pigeon Chest D. Skull Bones of the skull (cranium) develop around the developing brain. It is the brain that dictates what is going to be the shape and size of the skull Figure 13. Ribs and Sternum Cranial to the first cervical somite there are four occipital somites Mesenchyme arising from the sclerotome of these somite helps to form part of the base of the skull in the region of occipital bone ANOMALIES OF THE STERNUM AND RIBS Other mesenchyme contributing to the formation of the skull: Failure of the fusion of these 2 sternal bars will result to some pathologies ○ Otic vesicle - region of the developing ear ○ Nasal capsule - region of the developing nose 1. Sternal Cleft (depression near xiphoid process) Sclerotome is located at the paraxial part of the dermal region. Sternal bars do not fuse completely Fairly common TWO DIVISIONS OF THE SKULL: No clinical significance of it is small 2. Pectus excavatum (funnel chest/cave chest) 1. NEUROCRANIUM Most common chest anomaly Consists of the flat bones of the skull (cranial vault) and the base of (+) depression of the chest wall extending from the skull. the manubrium to xiphoid process Develops from neural crest cells patient demonstrates: Except: basilar part of the occipital bone (formed from the a. Cardiopulmonary restriction mesoderm of the occipital sclerotome) b. Drooped shoulders ○ Sub-divisions: c. Protuberant abdomen Chondrocranium d. Scoliosis Forms the bones of the base of the skull Formed by occipital sclerotomes Membranous neurocranium Forms the bones of the vault of the skull 1A. CHONDROCRANIUM (Base of the Skull/Floor of the skull) Base of the developing cranium. Can be noticed when you cut the skull bone axially and viewed from the top. Formed by fusion of several cartilages Three cartilaginous centers of the cranial base (2nd month) 1. Parachordal cartilages: appear around cephalic part of notochord in the otic-occipital region 2. Polar cartilages: appear around hypophysis cerebri in the Figure 14. Chest Anomaly: Funnel chest/Cave chest region of sphenoid 3. Orbitosphenoid/Alisphenoids/Trabeculae cranii - appear 3. Pectus carinatum (pigeon chest) between otic and nasal capsules that form the internal reverse of Pectus excavatum ear and the nasal cavity respectively. Fusion of the Pectus= breast/chest ; pectoralis muscle cartilages forms the various parts of the skull. Page 6 of 9 [EMBRYOLOGY] 1.10 EMBRYONIC DEVELOPMENT OF THE SKELETAL SYSTEM – Dr. Steve S. Arellano, MD 1B. MEMBRANOUS NEUROCRANIUM (Vault of the Skull) Intramembranous ossification occurs in the mesenchyme of the side and top of the brain forming calvaria (cranial vault). This mesenchyme also receives contributions from the neural crest cells. 2. VISCEROCRANIUM (Facial Skeleton) Consists the bones of the face involving the pharyngeal arches Develops from the neural crest cells Except: laryngeal cartilages (from mesoderm within the pharyngeal arches 4 and 6) Figure 17. Skull of a newborn seen from above (A) and the right side (B). Note the anterior and posterior fontanelles and sutures. The posterior fontanelle closes about 3 months after birth; the anterior fontanelle closes around the middle of the second year. Many of the sutures disappear during adult life. Fontanelles - large, fibrous areas where several sutures meet Six fontanelles: 1. Anterior fontanelle - largest fontanelle, palpable in infant, pulsates due to underlying cerebral arteries. Closes at 2 years of age. 2. Posterior fontanelle- Closes at 6 months of life. 3. Two sphenoid fontanelles Figure 16. The Facial Skeleton 4. Two mastoid fontanelles Divisions: 1. Cartilaginous viscerocranium - derived from cartilaginous skeleton (1st and 2nd pharyngeal arches) 2. Membranous viscerocranium - formed by intramembranous ossification of the maxillary prominence (1st pharyngeal arch), also receives contribution from neural crest cells. Bones that are partly formed in the cartilage and partly in the membrane: 1. Occipital bone: formed by an endochondral ossification, except the interparietal part (from membrane). 2. Sphenoid bone – cartilage bone, except lateral part of the greater wing & pterygoid laminae (from membrane). 3. Temporal bone – squamous & tympanic parts (from membrane), petrous and mastoid parts are formed by ossification of the cartilage of the otic capsule, styloid process is derived from cartilage of the 2nd branchial arch Figure 18. Fontanelles and Sutures of the Skull 4. Mandible – most of the bone is formed in membrane ANOMALIES OF THE SKULL *Sutures – during fetal life and infancy: flat bones of the skull are separated by dense connective tissue (fibrous joints). 1. Microcephaly failure of the brain to grow and usually associated with mental Five sutures: retardation. Chances are, you would develop mental disorders 1. Frontal suture 2. Oxycephaly (turricephaly or acrocephaly) 2. Sagittal suture tower-like-skull or pointed skull caused by the premature closure of 3. Lambdoid suture - triangular the lambdoid and coronal suture 4. Coronal suture 3. Plagiocephaly 5. Squamous suture asymmetrical skull caused by premature closure of coronal and lambdoid suture on one side of the skull; asymmetrical union of Allow flat bones of the skull to deform during childbirth (molding) & to expand sutures result in a twisted skull during childhood as the brain grows. 4. Brachycephaly Molding may exert considerable tension at the “obstetrical hinge” or the short, square shaped skull caused by premature closure of coronal junction of the squamous & lateral parts of the occipital bone, such that the sutures great cerebral vein of Galen may be ruptured during childbirth. 5. Scaphocephaly long skull (anterior/posterior plane) caused by premature closure of the sagittal suture. 6. Anencephaly greater part of the vault of skull is missing; eyebrows are directly continuous with the hair because major part of the vault of the skull is missing 7. Congenital hydrocephalus bones of the vault of the skull are separated by expansion of the cranial cavity. Page 7 of 9 [EMBRYOLOGY] 1.10 EMBRYONIC DEVELOPMENT OF THE SKELETAL SYSTEM – Dr. Steve S. Arellano, MD 8. Cleidocranial dysostosis Forelimb buds deformities of the skull are associated with the absence of clavicle ○ derived from part of the body wall belonging to segments 9. Kleeblattschadel (C4 to T2) German word; cloverleaf skull caused by premature closure of all ○ innervated by the corresponding spinal nerves sutures forcing the brain growth through the anterior and sphenoid fontanelles ○ appear earlier than the hindlimbs buds 10. Pfeiffer syndrome ○ each grows and becomes subdivided by constrictions into AD genetic DSO; caused by a mutation in the FGFR1 gene on arm, forearm, hand and digits. chromosome 8p12 ○ interdigital areas show cell death of which the digit Clinical Features: separates from each other a. Craniosynostosis leading to turribrachycephaly ○ in later development, the forelimb is adducted to the side b. Syndactyly of hand and feet of the body c. Broad thumbs and great toes Hindlimb bud 11. Crouzon syndrome ○ Formed opposite the segments (L2 to S2) AD genetic DSO caused by mutation in the FGFR2 gene on chromo 10q25. MOLECULAR REGURGITATION OF LIMB BUD DEVELOPMENT Clinical features: a. Premature craniosynostosis Three centers in the limb bud determine the three limb axes b. Midface hypoplasia with shallow orbits 1. Apical ectodermal ridge (AER) c. Ocular proptosis - Determines the proximal and distal segments d. Mandibular prognathism - Has an inducing effect on the underlying e. Normal extremities mesenchyme causing it to remain f. Progressive hydrocephalus undifferentiated and to proliferate. g. No mental retardation two AERs are formed on a limb bud 12. Apert syndrome - Results in formation of AD genetic DSO caused by a mutation in the FGFR2 gene on chromo supernumerary limbs. 10q25.3 no AERs formed: Clinical features: - Leads to failure of growth and a. Craniosynostosis leading to turribrachycephaly differentiation of limb; results in b. Syndactyly of hands and feet phocomelia. c. Various ankylosis d. Progressive synostoses of the hands and feet, and cervical 2. Zone of Polarizing Activity (ZPA) - determines the cranial spine to caudal axis (preaxial and postaxial margins) e. Mental retardation 3. Dorsal and Ventral ectoderm - determines dorsal and ventral axes V. FORMATION OF LIMBS VI. JOINTS Mesenchyme of the limb buds: ○ forms bones of the limb, shoulder and pelvic girdles except: clavicle (membrane bone) Derived from the mesenchyme intervening between bone ends ○ also gives rise to bones, connective tissues, and some Mesenchyme differentiation: blood vessels ○ Fibrous joint (syndesmosis) - formed from fibrous tissue ○ derived from the lateral plate mesoderm ○ Cartilaginous joint (synchondrosis) - formed from ○ all are formed by endochondral ossification cartilage; cartilage connecting the bones is later ossified Limb buds and two bones become continuous ○ Paddle-shaped outgrowth that arises from the side wall of Example: between the diaphysis and epiphysis the embryo at the beginning of the 2nd month of IUL of long bones ○ Mass of mesenchyme covered by ectoderm ○ Synovial joint ○ Muscles of the limbs are derived from myotomes and somites Mesenchyme usually seen in three layers: ○ Mesenchymal cells will form cartilaginous models which ○ Two outer layers will ossify to form the bones of the limbs continuous with the perichondrium ○ Each bud has a preaxial border and postaxial border (outermost surface of the cartilaginous end of ○ Thumb, great toe, tibia and radius are formed on the bone) covering the cartilaginous ends of the preaxial border articulating bone. ○ Middle layer becomes loose and forms a cavity cavity will be lined with mesothelium that forms the synovial membrane synovial capsule and other ligaments are derived from the surrounding mesenchyme. Common example is the knee joint joint between femur and tibia. ANOMALIES OF THE LIMBS: Figure 19. Formation of the upper limbs 1. Phocomelia (Amelia): A- absent; Melia - limb Page 8 of 9 [EMBRYOLOGY] 1.10 EMBRYONIC DEVELOPMENT OF THE SKELETAL SYSTEM – Dr. Steve S. Arellano, MD - one or more limbs of the body is partially or completely absent B. Bones of the shoulder, hip girdle and limbs arise from the lateral - produced by ingestion of harmful drugs plate mesoderm 2. Talipes Equinovarus - Talipes means club foot C. Some bones of the face and skull are derivatives of the pharyngeal - Most common variety of deformity arch’s mesoderm - Foot shows marked plantar flexion or medial flexion (equinus: horse ) D. All of the above & (varus: inversion) E. None of the above - Inward folding of foot that is downward 8. Which of the following statements is/are true regarding the vertebral - Opposite: Talipes Equinovalgus - foot is downward but everted column? 3. Syndactyly A. It is formed from the dermatome - Adjoining digits are fused B. Sclerotome cells are converted into tight mesenchyme - Digits of puppets, cartoons, ninja turtles C. Mesenchyme migrates laterally & surrounds the notochord 4. Macrodactyly D. Mesenchyme extends backward & surrounds the neural tube - A digit is abnormally large E. All of the above 5. Brachydactyly F. None of the above - A digit is abnormally short 9. It has an inducing effect on the underlying mesenchyme causing it to remain 6. Arachnodactyly (spider fingers) undifferentiated and to proliferate. - Fingers are long and thin A. Zone of Polarizing Activity (ZPA) 7. Polydactyly B. Apical ectodermal ridge (AER) - Supernumerary digits are present C. Dorsal and Ventral ectoderm 8. Lobster claw 10. It is a paddle-shaped outgrowth that arises from the side wall of the embryo - palm or sole may show a deep longitudinal cleft at the beginning of the 2nd month of IUL which comes from a mass of 9. Achondroplasia mesenchyme covered by ectoderm. - limbs may remain short A. Forelimb buds 10. Congenital dysplasia B. Limb buds - bone ends forming a joint are imperfectly formed C. Hindlimb bud - leads to congenital dislocation - the hip joint is most commonly affected because it is the part where you will suspend all your weight. Answers: 1. A 2. C 3. B 4. B 5. B 6. C 7. E 8. D 9. B 10. B TEST YOUR KNOWLEDGE REFERENCES 1. At the end of 3rd week, dorsolateral column become segmented and it’s Sadler, T. W., et.al. (2019). Langman's medical embryology (14th ed.). Lippincott called Williams & Wilkins. A. Somite Katzung, B. G. (2017). Basic and clinical pharmacology (14th ed.). McGraw-Hill B. Myotome Education. C. Mesenchyme Arellano, L.P. PPT Lecture 2. Which of the following is the key factor in osteoblast ossification? A. Sclerotome B. Osteocytes C. Wnt signaling D. Intramembranous membrane 3. Which of the following is TRUE? A. Chondrocytes that are outside of the perichondrium are surrounded by a space called matrix. B. Chondroblasts that exists in the perichondrium don’t have a lacunae C. The matrix is produced by the lacune 4. It determines the lineage commitment of skeletal precursor cells to chondrocytes and osteoblasts A. UMPS B. Beta-Catenin C. TGF-Beta 5. Components of the axial skeleton except: A. Ribs B. Pelvic bone C. Skull D. Vertebral column E. None of the above 6. Which of the following is the most common chest anomaly characterized with depression of the chest wall extending from the manubrium to xiphoid process? A. Sternal cleft B. Pectus Carinatum C. Pectus Excavatum D. None of the above 7. The following statements are true regarding the intraembryonic mesoderm except: A. Bones of the axial skeleton are derived from sclerotomes and head mesoderm Page 9 of 9