What is the Epidermis?
The human body has three main levels of skin. Starting from the deepest, they are the hypodermis, the dermis, and the epidermis. The epidermis is the outmost layer of skin. Any external area of skin is considered the epidermis – for example, the face, arms, and scalp.
What is the Purpose of the Epidermis?
The epidermis’ main purpose is to keep foreign bacteria out while retaining important fluids, water especially. It is also what protects the organs, nerves, and circulatory system from physical damage.
The Different Layers of the Epidermis
While there are three main levels of skin, the epidermis itself can have up to five sublayers. The number of sublayers varies in location throughout the body. The five layers are:
- Stratum corneum – this is the most external layer of the epidermis. It is made of dead skin cells (keratinocytes) that have become keratinized, meaning that they have become waterproof by producing a protein called keratin. This fully keratinized skin can now safely survive the elements.
- Stratum lucidum – this is just beneath the stratum corneum, and only found in the palms and soles. The keratinocytes have died, but are still undergoing the keratinzation process. This is what gives the palms and soles their added thickness.
- Stratum granulosum – also known as the “granular layer”, this is where keratinocytes secrete lamellar bodies, cellular structures which creates a water-repellant (hydrophobic), fatty membranes out of lipids. A number of other biological processes occur as enzymes, proteins, and lipids prepare the skin for shedding, and allows the keratinocytes to move up into the stratum corneum or lucidum.
- Stratum spinosum – a vital purpose of this skin layer is to retain moisture. This layer is what keeps the skin moist, and prevents the skin from drying and cracking. Skin conditions that have to do with dryness or cracking are usually caused by a malfunction within this skin layer, genetic or otherwise. This is also where keratinocytes first secrete lamellar bodies.
- Stratum basale – this is the deepest level of the epidermis. It is made almost entirely of keratinocytes. This is where desmosomes are produced, structures that attach cells together during a process known as mitosis. Without desmosomes, cells could not combine, and skin could not grow. Merkel cells can also be found here to help regulate and perceive the skin’s sensitivity to touch. Melanocytes are found here as well. The main role of melanocytes is to protect the skin’s DNA from damage, but it also controls the skin’s pigmentation, too.
Is Scalp Skin Different than Normal Skin?
Scalp skin is much thicker than skin found elsewhere on the body, and has an excellent blood supply. The scalp’s skin, muscle, and connective tissue are integrated together, which is what gives the scalp its extra elasticity. The scalp also has an abundance of sebaceous oil glands compared to elsewhere on the body. Sebaceous oil glands help keep the hair well-lubricated and allows for the hair shaft to make a smooth transition up the hair follicle and past the scalp.