| | Key Takeaway | | :--- | :--- | | Gametogenesis | Reduction of chromosomes via meiosis; importance of nondisjunction leading to trisomies (e.g., Down syndrome). | | First Week | Fertilization, cleavage, blastocyst formation, and implantation. | | Second Week | Bilaminar germ disc formation; development of the amnion, yolk sac, and chorion. | | Third Week | Gastrulation – the formation of the three germ layers: ectoderm, mesoderm, and endoderm. This is the most critical period. | | Organogenesis | Weeks 4-8: All major organs form. Most birth defects originate here. | | Fetal Period | Weeks 9-birth: Growth, maturation of tissues, and functional development of lungs and brain. | | Placenta & Membranes | Functions of the placenta (gas/nutrient exchange, endocrine production) and the clinical significance of umbilical cord abnormalities. |
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The journey of human embryology begins with fertilization, where a sperm fuses with an egg to form a zygote. This usually occurs in the fallopian tube and results in the formation of a diploid cell with 46 chromosomes. The zygote undergoes several cleavages, or cell divisions, without significant growth, leading to the formation of a morula. The morula is a compact cluster of cells that travels down the fallopian tube and into the uterus. | | Key Takeaway | | :--- |
Whether you are a student at a university like Nicolae Testemitanu SUMPh or a professional looking to refresh your knowledge, you can find the latest editions at major medical bookstores and digital platforms. | | Third Week | Gastrulation – the
: The book is packed with high-quality illustrations and scanning electron micrographs that help students visualize 3D changes over time.
During organogenesis, the embryo undergoes significant morphological changes, including the formation of the neural tube, heart, and limb buds. The neural tube eventually gives rise to the brain and spinal cord, while the heart develops into a functional circulatory system. The limb buds develop into the arms and legs, which will eventually undergo morphogenesis to form the characteristic human limbs.