Birth defects are developmental disorders that do not give an individual an odd appearance. Such developmental disorders can arise at different stages of development.
In the floor of the amniotic cavity, the macroblast of the chrysalis differentiates into two distinct layers, one consisting of tall cylindrical cells, forming the outer embryonic leaf.
During the 4th week, the proliferation of body cavity epithelial cells, and consolidation of the underlying mesenchymal tissue, created the gonadal ridge.
After being formed in the seminiferous tubule, at this time the sperm has a characteristic shape but has not yet been able to move, from the seminiferous tubule, sperm to the epididymis.
In men, cells of the spermatic lineage reproduce, differentiate, and progress to eventually produce spermatozoa, spermatocytes, spermatocytes 1, spermatozoa 2, pre-sperm, and spermatozoa.
The kidney and ureter arise from two intermediate dermal bands, called the nephrogenic band, which lie along each side from the head to the tail of the embryo, and interspersed between the primitive segments.
Around the middle of the 3rd week, the endoderm in the distal anterior intestine thickens to form an anterior germ called the primordial liver germ.
When two endocardial ducts merge, the visceral lamina of the pericardial cavity produces the myocardium and the visceral pericardium, the mesenchymal cells adjacent to the endothelium forming the endocardium.