The skin is the largest organ in the body, covering the entire external surface and serving as a primary protective barrier against the environment. It's composed of three main layers: the epidermis, dermis, and hypodermis.
Epidermis
The outermost layer, the epidermis, is made up of stratified squamous epithelium and contains four distinct cell types:
- Keratinocytes: These are the most abundant cells in the epidermis and produce keratin, a tough protein that forms the protective outer layer of skin.
- Melanocytes: These cells produce melanin, the pigment that gives skin its color and helps protect against UV radiation.
- Langerhans cells: These are immune cells that help fight off infections.
- Merkel cells: These cells are involved in touch sensation.
Dermis
The dermis lies beneath the epidermis and is responsible for the skin's strength and elasticity. It contains:
- Collagen and elastic fibers: These provide structural support and give the skin its flexibility.
- Blood vessels: These supply the skin with nutrients and oxygen and remove waste products.
- Lymph vessels: These help to drain excess fluid from the skin.
- Hair follicles: These are the structures that produce hair.
- Sweat glands: These produce sweat, which helps regulate body temperature.
- Sebaceous glands: These produce sebum, an oily substance that helps keep the skin moisturized.
- Nerves: These provide sensory information to the brain, allowing us to feel touch, pressure, pain, and temperature.
Hypodermis
The deepest layer, the hypodermis, is also known as the subcutaneous layer. It anchors the skin to the underlying muscle and bone, and contains:
- Fat cells: These provide insulation and cushioning for the body.
- Blood vessels: These supply the hypodermis with nutrients and oxygen.
- Nerves: These transmit signals to and from the brain and spinal cord.
