07/09/2013
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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 of the dermis are the papillary and reticular layers.
The upper, papillary layer, contains a thin arrangement of collagen fibers.
The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged parallel to the surface of the skin.
Specialized Dermal Cells
The dermis contains many specialized cells and structures.
The hair follicles are situated here with the erector pili muscle that attaches to each follicle.
Sebaceous (oil) glands and apocrine (scent) glands are associated with the follicle.
This layer also contains eccrine (sweat) glands, but they are not associated with hair follicles.
Blood vessels and nerves course through this layer. The nerves transmit sensations of pain, itch, and temperature.
There are also specialized nerve cells called Meissner's and Vater-Pacini corpuscles that transmit the sensations of touch and pressure.
Subcutaneous Tissue
The subcutaneous tissue is a layer of fat and connective tissue that houses larger blood vessels and nerves. This layer is important is the regulation of temperature of the skin itself and the body. The size of this layer varies throughout the body and from person to person.
The skin is a complicated structure with many functions. If any of the structures in the skin are not working properly, a rash or abnormal sensation is the result. The whole specialty of dermatology is devoted to understanding the skin, what can go wrong, and what to do if something does go wrong.
These are fat cells that conserve body heat while protecting other organs from injury. They provide a cushioning effect and are a source of energy in lean times.
Thickness of layer varies - the thinnest layer is on our eyelids making them light and flexible, the thickest is on our hands and feet for gripping.
Functions of Skin
This skin provides a protective layer for organs and tissues from pathogens, heat and light. It regulates body temperature. It stores water, fat and Vitamin D and has touch receptors that sense pain or pleasure. Skin is an excretory and absorption organ.
Skin has a natural moisturising factor (NMF). Teen skin is prone to oiliness as hormones are regulating. At 20-30 years skin cell turnover provides optimum condition. At 30-40 years cell turnover starts to decrease and fine lines start to appear. At 40-50 years skin becomes more dry. Over 50 years of age, cell turnover drops by 50% resulting in flaky patches and deeper lines.
The skin may be sensitive. Sensitive skin reddens easily due to environmental changes or cosmetic products. Skin can become permanently sensitive due to allergy, shaving, and use of skin care productscontaining alpha hydroxy and retinoic acid skin.
Skin has several jobs
It holds the body together
It stops water and body fluids from leaking out of the body.
It stops germs and dirt from getting into the body.
It senses how things feel (touch).
It can sense the temperature of things.
It can tell you when you have been hurt (pain).
It is waterproof so that rain slides off.
