Final answer:
The epidermis is the skin's outermost protective layer, lacking blood vessels and containing melanin-producing melanocytes. The stratum spinosum is a layer within the epidermis, characterized by its spiny appearance when stained.
Step-by-step explanation:
The epidermis is the outermost layer of the skin and is made up primarily of tightly packed epithelial cells. It serves as the body's protective outer barrier, being waterproof and responsible for the skin's overall appearance. The epidermis consists of several sub-layers, with the stratum spinosum situated just above the stratum basale. The cells in this layer are linked by desmosomes, which give the appearance of a spiny texture in stained samples, despite this texture not being present in unstained samples. Within the epidermis, melanocytes are responsible for producing melanin, the pigment that determines skin and hair color. It's noteworthy that the epidermis does not contain any blood vessels; nutrients are received through diffusion from the dermal blood vessels.