Skin
Layers of the skin
The skin is an ever-changing organ that contains many specialized cells and structures. The skin functions as a protective barrier that interfaces with a sometimes-hostile environment. It is also very involved in maintaining the proper temperature for the body to function well. It gathers sensory information from the environment, and plays an active role in the immune system protecting us from disease. Understanding how the skin can function in these many ways starts with understanding the structure of the 3 layers of skin - the epidermis, dermis, and subcutaneous tissue.
Epidermis
The epidermis is the outer layer of skin. The thickness of the epidermis varies in different types of skin. It is the thinnest on the eyelids at .05 mm and the thickest on the palms and soles at 1.5 mm.
The epidermis contains 5 layers. From bottom to top the layers are named:
* stratum basale * stratum spinosum * stratum granulosum * stratum licidum * stratum corneum
The bottom layer, the stratum basale, has cells that are shaped like columns. In this layer the cells divide and push already formed cells into higher layers. As the cells move into the higher layers, they flatten and eventually die.The top layer of the epidermis, the stratum corneum, is made of dead, flat skin cells that shed about every 2 weeks.
Specialized Epidermal Cells
There are three types of specialized cells in the epidermis.
* The melanocyte produces pigment (melanin) * The Langerhans' cell is the frontline defense of the immune system in the skin * The Merkel's cell's function is not clearly known Dermis
The dermis also varies in thickness depending on the location of the skin. It is .3 mm on the eyelid and 3.0 mm on the back. The dermis is composed of three types of tissue that are present throughout - not in layers. The types of tissue are:
* collagen * elastic tissue * reticular fibers
Layers of the Dermis
The two layers
The skin is an ever-changing organ that contains many specialized cells and structures. The skin functions as a protective barrier that interfaces with a sometimes-hostile environment. It is also very involved in maintaining the proper temperature for the body to function well. It gathers sensory information from the environment, and plays an active role in the immune system protecting us from disease. Understanding how the skin can function in these many ways starts with understanding the structure of the 3 layers of skin - the epidermis, dermis, and subcutaneous tissue.
Epidermis
The epidermis is the outer layer of skin. The thickness of the epidermis varies in different types of skin. It is the thinnest on the eyelids at .05 mm and the thickest on the palms and soles at 1.5 mm.
The epidermis contains 5 layers. From bottom to top the layers are named:
* stratum basale * stratum spinosum * stratum granulosum * stratum licidum * stratum corneum
The bottom layer, the stratum basale, has cells that are shaped like columns. In this layer the cells divide and push already formed cells into higher layers. As the cells move into the higher layers, they flatten and eventually die.The top layer of the epidermis, the stratum corneum, is made of dead, flat skin cells that shed about every 2 weeks.
Specialized Epidermal Cells
There are three types of specialized cells in the epidermis.
* The melanocyte produces pigment (melanin) * The Langerhans' cell is the frontline defense of the immune system in the skin * The Merkel's cell's function is not clearly known Dermis
The dermis also varies in thickness depending on the location of the skin. It is .3 mm on the eyelid and 3.0 mm on the back. The dermis is composed of three types of tissue that are present throughout - not in layers. The types of tissue are:
* collagen * elastic tissue * reticular fibers
Layers of the Dermis
The two layers