Integumentary System: Skin LayersDermis
The layer beneath the epidermis is the dermis. This is the thickest layer of skin composing almost 90 percent of its thickness. This layer contains specialized cells that help regulate temperature, fight infection, store water and supply blood and nutrients to the skin. The specialized cells of the dermis also help in the detection of sensations and give strength and flexibility to the skin. Components of the dermis include:
- Blood vessels - transport oxygen and nutrients to the skin and remove waste products. These vessels also transport vitamin D from the skin to the body.
- Lymph vessels - supply lymph (milky fluid containing white blood cells of the immune system) to skin tissue to fight microbes.
- Sweat glands - regulate body temperature by transporting water to the skin's surface where it can evaporate to cool down the skin.
- Sebaceous (oil) glands - secret oil that helps to waterproof the skin and protect against microbe build-up. They are attached to hair follicles.
- Hair follicles - tube-shaped cavities that enclose the hair root and provide nourishment to the hair.
- Sensory receptors - nerve endings that transmit sensations such as touch, pain, and heat intensity to the brain.
- Collagen - tough structural protein that holds muscles and organs in place and gives strength and form to body tissues.
- Elastin - rubbery protein that provides elasticity and makes the skin stretchable. It is also found in ligaments, organs, muscles and artery walls.
The innermost layer of the skin is the hypodermis. Composed of fat and loose connective tissue, this layer of the skin insulates the body and cushions and protects internal organs from injury. The hypodermis also connects skin to underlying tissues through collagen, elastin and reticular fibers that extend from the dermis. A major component of the hypodermis is a type of specialized connective tissue called adipose tissue that stores excess energy as fat. Blood vessels, lymph vessels, nerves and hair follicles also extend through this layer of the skin.
SEER Training Modules, Module Skin Cancer: Melanoma. U. S. National Institutes of Health, National Cancer Institute. 3, March 2010 .