The mesoderm also gives rise to the gonads as well as

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- The mesoderm also gives rise to the gonads as well as the muscular & connective tissue layers of the digestive and respiratory systems and the adrenal cortex - Endoderm: - The innermost layer is the endoderm and it becomes much of the epithelial linings of the digestive and respiratory tract, including the lungs - The endoderm also forms parts of the pancreas, thyroid, bladder, and distal urinary tracts as well as parts of the liver - Early Developmental Stages: Differentiation:
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- Cells with the same genes are able to develop into such distinctly different cell types with highly specialized functions through the selective transcription of the genome - In other words, only the genes needed for that particular cell type are turned on, while these same genes are turned off in other cell types - Selective transcription is often related to the concept of induction , which is the ability of one group of cells to influence the fate of nearby cells - This process is mediated by chemical substances called inducers, which diffuse from the organizing cells to the responsive cells - Induction also ensures the proximity and location of different cell types that work together within a specific organ - Early Developmental Stages: Neurulation: - Neurulation , the development of the nervous system, begins after the formation of the three primary germ layer cells - Formation of the nervous system begins with a rod of mesodermal cells known as the notochord forming along the axis of the organism like a primitive spine - The notochord then induces a group of overlying epidermal cells to slide inward to form the neural folds , which surround a neural groove - The neural folds grow toward one another until they fuse into a neural tube , which gives rise to the central nervous system - At the top of each neural fold are neural crest cells , which form the peripheral nervous system (sensory ganglia, autonomic ganglia, adrenal medulla, and schwann cells) as well as specific cell types in other tissues such as calcitonin producing cells of the thyroid, melanocytes in the skin, and others - Finally at the end of neurulation, the ectodermal cells will migrate over the neural tube and crest to cover the basic nervous system - Early Developmental Stages: Problems in Early Development: - Early development is a highly sensitive time and during this stage, as the germ layers are forming & organogenesis begins, tetragons can have highly detrimental effects - Teratogens are substances that interfere with development, causing defects of even death of the developing embyro - In addition to genetics the route of exposure, length of exposure, rate of placental transmission, and exact identity of the teratogen will also affect the outcome
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- Some common teratogens include alcohol, prescription, drugs, viruses, bacteria, and environmental chemicals including polycyclic aromatic hydrocarbons - Maternal health conditions can also affect development, including diabetes (increased fetal size and hypoglycemia after birth) and folic acid deficiency (neural tube defects) 3.2: Mechanism of Development: - Mechanism of Development: Cell Specialization: Specification & Determination: -
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