Gastrulation: the process of forming 3 germ layers.

Histogenesis: the process of the germ layers differentiating into tissues.

1. Endoderm-innermost layer. ex) Lining of the digestive and respitory organs, thyroid
2. Mesoderm-middle layer. ex) muscle
3. Ectoderm-Outermost layer. ex) skin, nervous, epidermis tissue

1. Membranous epithelium-lining/covering
2. Glandular epithelium-secreting

1. Protection-ex) skin
2. Sensory-ex) skin, nose, eye ear
3. Secretion-ex) hormones, digestive juices
4. Absorbtion-ex) small intestine, lungs
5. Excretion-ex) urine, sweat

1. Limited extracellular space or matrix; cells appear tightly packed
2. Apical surface-free suface exposed to the body exterior or the cavity of an internal organ
3. Basement surface-membrane-bottom surface (always close to a free edge)
4. Avasascular-no blood vessels; use diffusion
5. Innervated-contains nerve fivers (Nerves in it)
6. Original in ectodermal, mesodermal, and endodermal
7. High regeneration capacity

Columnar cells

1. simple-single layer
2. stratified-more than one layer

combination of cells such as squamous and cuboidal; irregular mixture

ex) bladder wall-stretchable