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Blastocyst Development: Day 3-5
The blastocyst consists of cells forming an outer trophoblast layer, an inner cell mass, and a blastocoel. The entire embryo is formed by the inner cell mass and is the source of true embryonic stem cells.The blastocyst stage of development occurs in humans during the first and second week after fertilization. -
Implantation: Day 7-8
Implantation is the stage of pregnancy at which the embryo adheres to the wall of the uterus. In most human pregnancies the conceptus implants 8 to 10 days after ovulation -
Musculoskeletal System Development: Day 20
Majority of the connective tissue of the musculoskeletal system is formed by the mesoderm. the musculoskeletal system consist of skeletal muscle, bone, and cartilage. The musculoskeletal system forms when the mesoderm reaches the 4th week of development. -
Cardiovascular System- Heart Development Day: 22-23
In human embryos the heart begins to beat at about 22-23 days, with blood flow beginning in the 4th week. The heart is one of the embryo's earliest functioning organs. A key development of the heart is the separation of the heart into separate chambers. -
Gastrointestinal Tract Liver Development Day: 45
The transverse septum initially arises at an embryonic junctional site. The liver will begin to form with the support from the mesenchymal structure and the transverse septum. The livers initial embryonic function is mainly cardiovascular. -
Carnegie Stage 17 Day: 42-44
In the Ectoderm the sensory placodes (such as smell, vision, and hearing), lens pit, otocyst, nasal pit move ventrally. Features of the endocrine develop such as the thymus, parathyroid, thyroid, pancreas, and adrenal. -
Genital System Development Day:55
The male and female reproductive system are initially "indifferent", it is the product of the Y chromosome SRY gene that determines the gender. The genitals will form around day 55.
