| A | B |
|---|
| Gastrula | The blastocyst is now called this at the end of the 2nd week. |
| Primary Germ Layers | Ecotderm, Mesoderm, Endoderm |
| Ectoderm | Nervous system, special sensory organs, epidermis, hair, nails, glands of skin |
| Mesoderm | Muscle and bone tissue, bone marrow, heart and circulatory system (blood and blood vessels), lymphatic vessels, cartilaginous and adipose tissues, internal reproductive organs, kidneys, epithelial linings of body cavities |
| Endoderm | epithelial linings of respiratory and digestive tract, urinary bladder and urethra |
| Embryonic Stage | Weeks 2-8 |
| Chorion | the two layers that surround the embryo are formed during this time period |
| Chorionic Villi | It is formed from the embryonic tissue forms slender projections that grow into the endometrium |
| Embryonic Stage | Head and jaw appears Heart Beats-which forces blood through tiny blood vessels Tiny buds of the upper and lower limbs form |
| Weeks 5-7 | Head grows rapidly and becomes rounded and erect |
| Weeks 5-7 | Face develops eyes, ears, and mouth and become more humanlike |
| Weeks 5-7 | Upper and lower limbs become longer and form tiny toes and fingers |
| Weeks 5-7 | All main internal organs are established by the end of the 7th week. |
| Week 8 | Chorion remains and forms a disk shaped area that becomes the placenta. |
| Week 8 | Chorionic Villi degenerate and we now have a placenta that keeps the baby attached to the endometrium. |
| Week 8 | Oxygen and nutrients from the maternal blood diffuses into the embryonic blood. CO2 and wastes from the embryonic blood diffuse into the maternal blood. |
| Placental Membrane | the membrane that separates the embryonic blood from the maternal blood. |
| Placenta | A vascular organ made from embryonic and maternal tissues |
| Placenta | The maternal portion originates from the endometrium and the embryonic portion originates from the chorion and its villi. |
| Placenta | Delivers nutrients and oxygen to the developing fetus. Removes wastes and carbon dioxide from the developing fetus. |
| Placenta | Produces the hormones estrogen and progesterone. Produces and release the hormones relaxin and HPL |
