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Histogenesis 511 Tissue diferentiation • Blastocyst differentiation: Cytotrophoblast Trophoblast Syncytiotrophoblast Epiblast Embryoblast Hypoblast Extraembryonic mesoderm Epiblast • Epiblast differentiation: Gametes Ectoderm Somatic cells Mesoderm Endoderm Histogenesis Derivatives of embryonic tissues • • • • • • • Ectoderm: CNS, retina PNS Epidermis, glands in skin, mammary gland, nails, hair Enamel Cell of neural crest: Spinal, autonomic glanglia, Schwann cells, melanocytes, medulla of adrenal gland, meninx, muscle, connective tissue and cartilage/bone of pharyngeal arches, dentin Mesoderm Intraembryonic mesoderm: • Axial mesoderm – notochord and cranial signaling center (prechordal plate) • Paraaxial – somites • Intermediate • Lateral: somatopleura, splanchnopleura and intraembryonic coelom • Cardiogenic zone Derivatives of mesoderm Mesoderm: • Connective tissue, cartilage, bone, muscles • Vessels, heart • Kidney, ovary, testes, oviduct, uterus, epididymis, differential duct ect • Spleen, lymph nodes, bone marrow • Suprarenal gland • Mesothelium Derivatives of endoderm Endoderm • Digestive tube and respiratory system (= epithelium and glands) • Thyroid gland • Parathyroid gland, thymus, • Pancreas including islets of Langerhans, liver • Epithelium of urinary bladder, urethra, vagina Axial structures od embryo ●Notochord ●Signaling – induction of development of ectoderm – neuroectoderm and ventral plate of future neural plate, in mesoderm – somites and endoderm = segmention ● It grows up to oropharyngeal membrane ● Prechordal plate – cranial organizer - induces prosencephalon development Paraaxial mesoderm • Cranial region – somitomeres – swirls of cells – head • From 8. somitomere – somites are formed • Somites (20th day) – successive development Somitogenesis Differentiation of somites – stimuli from notochord (Shh) and ectoderm (BMP) ● Different concentration of signal molecules ● Other signal molecules – Wnt, RA, FGF ● DERMATOMYOTOME - dermatome and myotome • SKLEROTOME Somitogenesis Sclerotome Somite Myotome Dermatome Somitogenesis • Association – development of somites Development of vertebrae • Vertebrae develop from sclerotome • Mesenchyme from sclerotome surrounds notochord (nucleus pulposus) • Vertebra consist of cranial and caudal part of the adjacent sclerotomes Development of vertebrae • Sklerotome is divided in cranial and caudal part • Nerve fibers are located within the space between both parts • Cranial and caudal parts of the adjacent somites fuse and form one vertebra Development of skeletal muscle • Myotome – • Epaxial muscle • Hypaxial muscle + muscle od limbs • Inervation is necessary – segmental spinal nerve Development of skeletal muscle • Cells in somite • Myoblasts - migrate and proliferate • Myotube – myoblasts fuse • Mature muscle fibre – actin and myosin are present – fully differentiate cell – they cannot divide Mesenchyme • Blood cells • Endothelium • Cells of connective tissue – fibroblast, mast cell, adipocyte, chondrocyt, osteoblast and osteocyt, odontoblast • Smooth muscle cell Development of neural tissue • Neural plate – restriction, determination and differenciation of ectoderm- signal molecules – interaction between epithelial and mesenchymal tissue • Cranio-caudal gradient – segmentation CNS (hox genes) • Cell proliferation – neural folds and neural groove, neural crest • Folds fuse – from cervical region to both sides – neuroporus anterior and neuroporus posterior • Neuroporus anterior and posterior – neural crest Development of CNS Brain is divided in 3 vesicles – prosencephalon, mesencephalon and rhombencephalon • Segments – neuromeres • Mechanism: expression of hox genes • Segmentation of spinal cord – induction – signals from mesoderm Development of brain Telencephalon Prosencephalon Diencephalon Mesencephalon Pons and cerebellum Rhombencephalon Medulla oblongata Development of nerve tissue • Germinal layer – proliferation of cells – future ependym • Cells migrate to mantle layer – neuroblasts – neurons – they enter permanent G0 phase • Other cells – glioblasts – radial glia (produces extracellular matrix as information for neurons) (Müller cells in retina) and glia – astrocytes and oligodendrocytes Proliferation of cells in CNS Development od CNS • Signaling from notochord and superficial ectoderm – histo-differenciation of neuroectoderm • Various types of neurons Neural crest • PNS • Melanocytes • Medulla of adrenal gland • Meninx Cranial neural crest • Development of head, pharyngeal arches and heart • PNS, melanocytes • Connective tissue, cartilage, muscle of pharyngeal arches Development of epidermis • Simple cuboid epithelium • Periderm – 2layers • Stratified squamous epithelium • Later, superficial cells get cornified Development of blood cells
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