The skin

The skin

1. Epidermis

   • Stratum Basale
     • a layer of single cells that lays on the basement membrane of the dermis. These cells continuously divide and push up towards the surface of the skin.
   • Stratum spinosum
     • These cells are “spiny” as the name denotes. They have been pushed out from the stratum basale and the spines interlock together to form a support layer.
   • Stratum granulosum
     • The cells of this layer are still living, but none of the nutrients reach them. These cells begin producing keratin and the cells begin to die. Eventually, the keratin protein produced will make up the majority of the dead cells in the next two layers.
   • Stratum lucidum
     • This layer of dead keratinized cells is only found in areas where skin is thick, such as the soles of the feet,and is not found in thin skin areas, such as the forearm.
   • Stratum cornuem
     • This is the outer layer that we see and is made up of layers of dead keratinized cells. This layer is tightly bound together, and the keratin protects the underlying cells from fluid loss while keeping the skin elastic. In a process called desquamation, cells of the stratum corneum are sloughed off. Cells from the epidermis are completely shed every 35-45 days, so essentially you have completely new skin every month and a half!
   • The epidermis is the outermost layer of the skin.There are four types of cells that make up the epidermis: melanocytes that produce melanin (influences skin color), keratinocytes that produce keratin, Merkel’s cells that function in touch, and Langerhans’ cells that function in immunity. There are a few layers, called strata,that make up the epidermis. The epidermis is avascular and all nutrients for the living cells of the epidermis diffuse from the basement membrane of the dermis below it

2. Hypodermis

   • The hypodermis is the bottommost layerof skin, located under the dermis. This layer is primarily made up of adipose tissue and functions in insulation and protection. The base of blood vessels, nerves, and some hair follicles also extend into the hypodermis.

3. Dermis

   • The dermis is the layer below the epidermis. The dermis is primarily made up of connective tissue layers and proteins including collagen, elastin, and reticular fibers. The arrangement of these fibers allow for the dermis to be extremely elastic and flexible. It also allows for blood vessels, glands, hair follicles, and nerves to be embedded in the dermis. The two main glands embedded in the skin include the sweat and sebaceous glands. The sweat glands assist the body in temperature control. The sebaceous glands produce oils that keep the outer layer of skin and hair moisturized. Hair and nail growth begin in the dermis. Highly keratinized epithelial cells are arranged to make up hair and nails.