-
Day 1
This is Fertilization Day one and is stage 1 of the secretory phase. Stage one is where the male and female pronuclei, containing DNA and chromosomes, at the middle have not combined to form one nuclei for the Zygote. The polar bodies on the side contain excess DNA and the Zona Peluida on the other side forms a thick extracellular layer around the egg and the developing conceptus for the first week. -
Day 20
This is stage 9 of the secretory phase. The embryo is now 1.5 to 2.5 mm and the first somites start to form the major body structures. The three main divisions of the brain can be distinguished. The neural crest and neural cells start to form and contribute to the development of skin, teeth, head, face and heart. -
Day 23
The heart begins to in humans on days 22-23 making it the first functioning embryonic organ formed. -
Day 32
This is stage 14 of the secretory phase. The heart, liver, umbilical cord become visible externally as bulges. Upper and lower limb buds start to grow and first appearences of future brain hemispheres. The abdominal wall of the body start to create the abdominal cavity. Vision lens placode is indented by the lens pit and liver hepatic gland and its vascular channels enlarge, hematopoietic function appears. -
Day 44
This is stage 19 of the secretory phase and it consists of a lot of the babys development. Vision sarts to develop as the eyelids open up, the cardiovascular system starts to form, the respiratory system starts to form, the gastrointestinal tract opens up, the renal opens up as urinary pressure pushes it in stage 18-19, the internal and external genitalia forms based on the gender of the baby. -
Day 54
This is stage 22 of the secretory phase. The limb fingers and toes lengthen and smell is being developed. The uterus vagina also form at around stage 22-23. -
Day 56
This is stage 23 of the secretory phase and marks the end of the embryonic period. This stage is when the head, nose, eye, eyelids, and external ears form. The body straightens and the upper limbs lengthen, bend at elbow, hands and feet turn inward, toes and fingers seperate and wrists form. The stomach starts to develop, the female development begins, the rectus muscle forms, and the vertebral columns form.
