Your epidermis is the outermost layer of your skin; it functions as a waterproof, protective covering over the entire surface of your body. There are several layers of your epidermis, each with its own unique structure and function.
The most superficial layer of your epidermis is called the Stratum Corneum. This layer is the oldest layer of skin in your body and is composed of essentially “dead” cells. These “dead” cells are “cornified” meaning they contain hardened, dense non-living connective tissue. The term “corns” comes from a condition in which the stratum corneum is excessively thickened to the point that it may become unattractive and require some sort of procedure to reduce its thickness.
Your stratum corneum functions as a barrier to protect the underlying tissues of your skin from damage caused by disease (infection) and loss of water (dehydration). Your stratum corneum also protects your less sturdy underlying skin from damage due to mechanical forces (like scratches and bruises) and from other stresses like extreme temperatures, harsh chemicals and other adverse environmental conditions.
Your stratum corneum is continually undergoing a process known as desquamation, where these dead, cornified cells are shed from the surface of your skin. These worn out, dead cells are being continuously replaced by new cells that form in the deepest layer of your epidermis known as the Stratum Basale. All of the cells within your epidermis are specialized cells called keratinocytes. Your Keratinocytes produce a very important material named Keratin, which is a sturdy type of connective tissue. It takes between 14-45 days (depending on your age) for the keratinocytes made in your Stratum Basale to migrate through your epidermis and become part of your Stratum Corneum.
Just below your stratum corneum is a layer of your epidermis called the stratum granulosum. (granular layer)This very thin layer of epidermal cells contains a granular material called keratohyalin. This important material helps to keep your stratum granulosum hydrated (filled with water) and it also helps bind your keratin together in a process known as crosslinking. Additionally the kerotinocytes of your stratum granulosum secrete a fatty, protein containing substance that is impenetrable to water (called lamellar bodies) into the space between your stratum granulosum and your stratum corneum. Therefore your stratum granulosum has a “waterproofing” function that protects the lower layers of your epidermis from becoming dehydrated.
Your Stratum Spinosum is the layer of your epidermis which lies just below your stratum granulosum. It is in this layer of epidermis that your cells start to become keratinized (filled with durable connective tissue). There are certain structures within your stratum spinosum that have a “spiny” appearance under a microscope, hence the term stratum spinosum.
The deepest (most basale) layer of your epidermis is know as the Stratum Basale. Your stratum basale is composed of a single layer of thick cells that have a multitude of cell types and functions. Most of your stratum basale is made up of keratinocytes (keratin producing cells). However, within your stratum base you also have melanocytes (cells that produce the pigment melanin that allows you to tan), Langerhans cells (which are part of your immune system) and Merkel cells (which contain touch receptors and allow you to feel things)
Your Dermis is the layer of your skin just underneath your epidermis. This important layer of skin has a multitude of important functions. Your dermis provides the blood supply to your epithelium. Therefore it is responsible for providing nourishment to your epidermis and simultaneously removing waste material from your epidermis. Additionally, your dermis is made up of very strong connective tissue that helps protect and cushion your body from stress and strain (a natural padding). Your dermis also contains many nerve endings which allows you to feel therefore providing you with the sense of touch and temperature. Your dermis also houses many other important structures like hair follicles, lymphatic vessels, blood vessels, and glands (sweat glands, sebaceous glands and apocrine glands).
Your dermis is composed of three major types of cells, fibroblasts (which created connective tissue), macrophages (an important part of your immune system) and adipocytes (fat cells which help to cushion and insulate your skin)
Your dermis is also composed of various types of connective tissue; collagen (a type of structural protein that provides strength to your skin), elastin (which allows your skin to be elastic and stretch yet, spring back to its original shape) and a gel-like substance between your skin cells composed of substances called glycosaminoglycans (hyaluronic acid, proteoglycans and glycoproteins).
Your dermis has two different areas: a superficial area just below your epidermis, called the papillary dermis and a deeper area called as the reticular region.
Your papillary dermis is composed of loose connective tissue. It has fingerlike projections (papillae) that help connect it to your epidermis. Your papillary dermis is mostly this loose connective tissue, small blood vessels (capillaries) and nerve bundles.
Your reticular dermis lies just below your papillary region and is much denser and thicker. It is made up of dense connective tissue that contains fibers made of collagen and elastin. These durable and elastic fibers are “cross-linked” to each other by what are known as reticular fibers (hence the term – reticular dermis). Also found in your reticular dermis are the roots of your hair follicles, various glands (sebum producing and sweat producing), nerve bundles, blood vessels, lymphatic vessels and nail beds.
The area just below your skin is called your Hypodermis. This region (also known as your subcutis or superficial fascia) is composed mostly of connective tissue and three types of cells, fibroblasts (which produce your connective tissue), adipose cells (which store fat) and macrophages (a very important part of your immune system. The main function of your hypodermis is to store fat (to be used as energy) and to insulate your body (from extreme temperatures and injury).