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Fertilization:Spermatozoa penetrate the corona radiata and zona pellucida, initiating fusion with the oocyte.
Formation of the zygote, the first diploid cell of the organism. -
1 week: Cleavage and Morula Formation:Rapid mitotic divisions lead to the formation of a solid sphere of totipotent cells, known as the morula. -
2 week Blastocyst Formation and Implantation:
Compaction of the morula results in the formation of the blastocyst.
The blastocyst undergoes apposition, adhesion, and penetration to implant into the endometrial lining. -
Gastrulation:
Formation of the three embryonic germ layers: ectoderm, mesoderm, and endoderm.
Establishment of the primitive streak guides cell migration to specific layers. -
Neurulation:
Induction of the neural plate leads to the development of the neural groove and neural folds.
Neural tube formation initiates, giving rise to the central nervous system. -
Formation of Basic Organ Systems:
Cardiovascular system development includes the formation of the heart tube and blood vessels.
Limb bud initiation leads to the development of upper and lower limbs.
Facial prominences develop, giving rise to eyes, ears, and distinct facial features. -
Fetal Period Begins:
Transition to the fetal period marked by the completion of organogenesis.
Rapid growth and specialization of tissues and organs. -
Development of External Genitalia:
Sexual differentiation progresses with the development of male or female external genitalia.
Gonadal differentiation influences the formation of the reproductive system. -
Quickening:
Maternal perception of fetal movement, known as quickening, becomes apparent.
Fetal movements result from the development of skeletal muscles and nervous system connections. -
Bone Formation and Growth:
Ongoing ossification involves intramembranous and endochondral processes.
Limb elongation driven by chondrocyte proliferation and hypertrophy. -
Vernix Caseosa and Lanugo Development:
Formation of vernix caseosa, a waxy substance protecting the fetal skin.
Emergence of lanugo, fine hair providing thermal insulation and sensory stimulation. -
Viability:
Fetal viability is achieved, with potential survival outside the womb with advanced medical care.
Maturation of organ systems, including the respiratory and digestive systems. -
Rapid Brain Development:
Synaptogenesis and neuronal migration contribute to rapid brain development.
Myelination enhances the efficiency of neural transmission. -
Fetal Adipose Tissue Accumulation:
Accumulation of adipose tissue contributes to weight gain and thermal regulation. -
Surfactant Production:
Fetal lungs produce surfactant, reducing alveolar surface tension.
Surfactant is crucial for lung function and postnatal respiratory adaptation. -
Continued Maturation and Reflex Development:
Maturation of remaining organ systems, preparing for extrauterine life.
Reflex development and readiness for the transition to the postnatal environment