Embryonic Development

1. What are the four initial stages of the embryonic development?
The four initial stages of the embryonic development are the morula stage, the blastula stage, the gastrula stage and the neurula stage.

2. What is the cell division during the first stage of the embryonic development called? How is this stage characterized?
The cell division in the first stage of the embryonic developments is called cleavage, or segmentation. In this stage several mitoses occur from the zygote forming the new embryo.

3. What are the cells produced in the first stage of the embryonic development called?
The cells that result from the cleavage (the first stage of the embryonic development) are called blastomeres. In this stage the embryo is called morula (similar to a “morus”, mulberry).

4. After the morula stage what is the next stage? What is the morphological feature that defines this stage?
After passing the morula stage in which the embryo is a compact mass of cells, the next stage is the blastula stage. In the blastula stage the compactness is lost and an internal cavity filled with fluid appears inside, the blastocele.

5. After the blastula stage what is the following stage of the embryonic development? What is the passage from blastula to the next stage called?
The blastula turns into gastrula in a process known as gastrulation.

6. What is gastrulation? How during gastrulation are the first two germ layers formed? What are these germ layers?
Gastrulation is the process through which a portion of the blastula wall undergoes invagination inside the blastocele, forming a tube called archenteron (primitive intestine). The cells of the inner side of the tube form the endoderm (germ layer) and the cells of the outer side form the ectoderm (another germ layer). It is the beginning of the tissue differentiation in embryonic development.

7. What are the three types of germ layers that form tissues and organs in animals?
The three germ layers are the ectoderm, the mesoderm and the endoderm.

Germ Layers

What are the three germ layers in humans and what differentiated tissue do they each form?
Endoderm
The endoderm is one of the germ layers formed during embryogenesis.The endoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the digestive tube excepting part of the mouth and pharynx and the terminal part of the rectum (which are lined by involutions of the ectoderm). It also forms the lining cells of all the glands which open into the digestive tube, including those of the liver and pancreas; the epithelium of the auditory tube and tympanic cavity; the trachea, bronchi, and air cells of the lungs; the urinary bladder and part of the urethra; and the follicle lining of the thyroid gland and thymus.

Mesoderm
The middle of the three germ layers, or masses of cells (lying between the ectoderm and endoderm), which appears early in the development of an embryo. In vertebrates it subsequently gives rise to muscle, connective tissue, cartilage, bone, notochord, blood, bone marrow, lymphoid tissue, and to the epithelia (surface, or lining, tissues) of blood vessels, lymphatic vessels, body cavities, kidneys, ureters, gonads (sex organs), genital ducts, adrenal cortex, and certain other tissues.

Ectoderm
The ectoderm is the start of a tissue that covers the body surfaces. It emerges first and forms from the outermost of the germ layers.The ectoderm forms: the central nervous system, the lens of the eye, cranial and sensory, the ganglia and nerves, pigment cells, head connective tissues, the epidermis, hair, and mammary glands.

here's a good way to remember

Ectoderm-- Attracto (what makes you attractive, eyes, epidermis(skin), nervous system(you get nervous when you're on your first date with an attractive woman

Mesoderm: Means: gonads(means of making kids) and all the systems except nervous system which is ur means of breathing(respiratory systems)means of having a heartbeat(circulatory system)

Endoderm: epitheal lining, urinary bladder, digestive organs, connective tissue