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Embryonic Development Anatomy & Embryology Teams 434 Embryonic Development Anatomy & Embryology Teams 434 If you have any complaint or suggestion please don’t hesitate to contact us on: [email protected] [email protected] Objectives • List the different parts of mesoderm and the different divisions of somites. • Differentiate bones according to their embryological origin and mode of ossification. • Describe the ossification of long bones. • Describe the main steps for development of limbs. • Differentiate muscles according to their embryological origin. Intraembryonic mesoderm: Proliferates between Ectoderm and Endoderm EXCEPT in the central axis of embryo where NOTOCHORD is found. Differentiates into 3 parts: Lateral Intermediate Paraxial mesoderm mesoderm mesoderm On each side of notochord. Divides into units (Somites) Divided by Intraembryonic coelom into: Somatic Splanchnic mesoderm mesoderm Between Between Ectoderm and Coelom Endoderm and Coelom DEVELOPMENT OF LIMBS The limb Bud appears as an elevation on the ventrolateral body wall resulting from proliferation of mesenchyme of the somatic layer of lateral mesoderm, Each limb bud is surrounded by an area of ectoderm. Upper limb buds Lower limb buds Appear at day 26 Appear at day 28 opposite the lower cervical segments. opposite the lumbar sacral segments Originally, limb buds were at right angle of the trunk with : Borders Surfaces Cranial Caudal Preaxial Postaxial Ventral Dorsal Radius and Tibia Flexor Muscles DEVELOPMENT OF LIMBS During 7th week Adduction of limb buds occurs with 90° rotation : In The Upper Limb In The Lower Limb Rotation occurs Laterally: Rotation occurs Medially: Radius Lateral Tibia Medial Flexor Anterior Flexor Posterior muscles muscles Helpful video http://www.youtube.com/watch?v=VpbdqGJ9LWk&channel=Itzy2512 DEVELOPMENT OF LIMBS Distal ends of buds Mesenchyme Mesenchyme fla]en into between rays Between digits paddle-like hand disappears to form disappear to . and foot plates notches. separate them Apical ectodermal Digital rays appear Digits form ridge: appears at the apex as Mesenchymal inside of limb bud and stimulates condensations that rays,elongate Proliferation of mesenchyme outline the patterns and appear And elongation of limb bud. of digits. webbed. DEVELOPMENT OF LIMBS There is in Paraxial Myoblasts to form Myotomes migrate from those Muscles mesoderm (somite) Myotomes to limbs of limbs Apical Ectodermal Ridge : Will induces growth of Mesenchyme and its transformation into cartilage. Mesenchyme from Lateral Mesoderm DEVELOPMENT OF BONES *All bones Develop from Mesoderm. *All bones Ossify by Endochondral Ossification EXCEPT: 1. Some bones of Skull 2. Clavicle . Appendicular Axial Skeleton Skeleton from Somatic Part of Lateral Mesoderm Vertebrae, Ribs and Sternum Skull from Sclerotomes from Mesoderm of Somites surrounding the Brain (Paraxial Mesoderm) DEVELOPMENT OF CRANIUM (SKULL) *The skull develops from Mesoderm around the developing brain. Protective case for brain Neurocranium Skeleton of face Viscerocranium There are two essential processes during fetal development of the skeletal system by which bone tissue is created Bones Cartilage Intramembranous Endochondral Ossification Ossification Ossification Of Long Bones OSSIFICATION OF LONG BONES BIRTH PUBERTY 1.Cartilaginous 2.Primary Ossific Centers 3.Secondary Ossific Centers 4.Ossification of State (Ossification of Diaphysis) (Ossification of Epiphysis) Epiphseal Plate Growth of bone stops Growth of Epiphyselplate of cartilage1 Diaphysis Epiaphysis 1: Bone increases in Length By proliferation of epiphyseal plate Cartilage Bone OSSIFICATION OF LONG BONES Bone age is a good index of general maturation. Bone age is determined by: Appearance of Ossific Disappearance of centers in diaphysis and epiphysis Epiphyseal Plate Specific for each Bone and Sex OSSIFICATION OF SKULL BONES Endochondral Intramembranous ossification ossification Frontal Parietal Zygomatic Squamous Mandible Maxilla Temporal JOINTS DEVELOPMENT Mesoderm differentiation into… Dense fibrous connective Fibrous joints tissue. Joints develop from Mesoderm Cartilaginous joints Cartilage between bones: Synovial Membrane Synovial joints Capsule Ligaments A synovial cavity is Formed inside mesoderm MUSCLES DEVELOPMENT From Ectoderm EXCEPTIONS: 1.Muscles of iris (eyeball). All muscles develop from Mesoderm 2.Myoepithelial cells of mammary & sweat glands. All Skeletal muscles develop Cardiac and Smooth muscles from Myotomes of develop from Paraxial Mesoderm Lateral Mesoderm EXCEPTIONS: Some Head & Neck muscles from mesoderm Smooth Muscles: Cardiac Muscles: of pharyngeal Arches. *In the wall of viscera: from from Splanchnic part of splanchnic part of lateral mesoderm Lateral Mesoderm. *In the wall of blood & lymphatic vessels: from somatic part of lateral mesoderm. SUMMARY Mesoderm Lateral Intermediate Paraxial mesoderm mesoderm mesoderm Somites Splanchnic Somatic gives gives 1.Cardiac muscles. 1.Appendicular skeleton. Sclerotomes Myotomes 2. Smooth muscles gives gives 2.Smooth muscles in the wall of Skeletal muscles: Axial skeleton in the wall of Blood & Lymphatic 1.Epaxial division. 1.Vertebral column. Viscera. vessels. (Muscles of the back) 2. Ribs 2. Hypaxial division. 3. Sternum (Muscles of body wall) 3. Myoblasts migrate into limb. (Muscles of limbs) MCQS 1.Proliferates between Ectoderm & Endoderm EXCEPT in: 6.Which one of the following bones ossifies by A-Somatic mesoderm. intramembranous ossification: B-Splanchnic mesoderm. A-Vertebra. C-central axis of embryo. B-Humerus. C-Ribs. 2.The limb Bud appears as an elevation on: D-Mandible. A-the ventrolateral body wall. B-area of ectoderm. 7. Regarding the ossification of long bones, which one of the C-lower cervical segments. following statement is correct: A-Primary ossific centre appears after birth. 3.During 7th week, adduction of limb buds occurs with: B-Secondary ossific centre leads into ossification of diaphysis. A-180 rotation. C-Long bones ossify by intramembranous ossification. B-90 rotation. D-When epiphysis unites with diaphysis, growth of bone stops. C-30 rotation. 4.Bone increases in length by proliferation of: A-Disphysis. B-Epiphysis. C-Epiphyseal Plate. 5.Which one of the following group of muscles are Answers: derivatives from epaxial division of myotomes: 1.C 6.D A-Muscles of back. B-Muscles of limbs. 2.A 7.D C-Muscles of viscera. 3.B D-Cardiac muscles. 4.C 5.A Done by: • Rana Aljunadiel • Futoon Almutari • Najd Alomran • Reema Alhammad • Najla Aldraiweesh • Rasha Bassas • Lama Alqahtani • Mash’hour Alzareie • Osama Abdulqader • Nouf Almasoud • Lamya Althawadi .
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