Anatomy of Human Skin
Anatomy of human skin is complex! The largest organ of the body spanning over twenty square feet in your average adult but less than the thickness of a tissue is an incredible organ. Human skin performing multiple functions including temperature regulation and detecting pressure and pain, water regulation and a barrier to the environmental agents that bombard it every day.
Three primary regions make up our skin the subcutaneous, the dermis and the epidermis. These regions can be further divided into their associated functions.
The Subcutaneous Region
The deepest layer of the skin comprised primarily of subcutaneous fat cells. Subcutaneous fat cells provide us with warmth and protection.
The dermis is housed between the subcutaneous region and the epidermis. Comprised of two regions the dermis has the reticular layer and the papillary layer. Fibers such as collagen and elastin which provide strength and flexibility are a main component of the dermis. Receptors that identify pain and pressure and temperature are found here.
The system that detects sensations associated with touch and feeling is called the Somato -sensory system. Comprised of mechanoreceptors, thermo receptors and nociceptors the somatosensory system has many functions. Mechanoreceptors are associated with pressure, touch and vibration. Thermo receptors refer to the nerve endings which detect temperature fluctuations and help regulate thermoregulation thermo receptors are capable of detecting temperatures as low as 10 degrees celcius and as high as 45 degrees celcius. If the temperature detected exceeds these ranges nociceptors are stimulated, indicating freezing or burning.
Nociceptors detect pain and are stimulated by harmful mechanical or heat stimuli.
The dermis can be likened to a bowl of jelly with fruit pieces scattered throughout. The fruit represents the two main fibers of the dermis collagen and elastin and the jelly is the substance called GAGS otherwise referred to as glycosaminoglycans. The jelly like substance or GAGS holds all the other components of the dermis in place and prevents everything from going south when you stand on your head! GAGS also acts as a transport highway for various chemical pathways and messages to reach their targets. Within this jelly collagen provides strength to the dermis and elastin that snap back that you find when you pinch your skin between your fingers.
The Epidermis is the upper most region of the skin. We can see touch and feel those outermost layers. The epidermis is comprised of several layers performing various functions
Stratum Germinativum also known as the stratum Basale is the inner most layer of the epidermis and is attached to the dermis via the basal lamina. The basal lamina is the interface between the dermis and the epidermis. The stratum basale is comprised of a single layer of columnar shaped cells – these cells undergo mitosis(cell division) and are also where the process of keratinization begins.
Stratum Spinosum is the next layer on our journey through the stratums and this layer is composed of several layers. The cells of the stratum spinosum are irregularly shaped and slightly separated from each other. There are intercellular bridges between these cells named desmosomes. There is no cell cytoplasm spanning these bridges. The cytoplasm within the cells is now comprised of filaments called tonofibrils, considered the precursors of keratin proteins.
The Stratum Granulosum comprised of up to four rows of diamond shaped cells, containing irregular shaped keratohyalin granules these granules are involved in the formation of keratin. As the granules increase in size and number the nucleus degenerates.
The Stratum Lucidum is a clear translucent layer evident in palms of hands and soles of the feet. These cells have no nuclei and the cytoplasm contains eleidin which is a transformation product of keratohyalin.
The Stratum Corneum is the outermost layer of non -living scale like cells which are flattened and joined together. The cytoplasm has been replaced by keratin protein. The most superficial layers of the corneum are sometimes referred to as the stratum disjunctum and where desquamation occurs.
Important cells also found in the epidermis
Melanocytes are the cells that produce the pigment melanin they are found beneath and between the basale cells of the epidermis. Melanocytes contain an enzyme called tyrosinase which is instrumental in the pathway of creating melanin pigment. Through various pathways melanin production is stimulated through the activity of tyrosinase acting upon the amino acid tyrosine. Melanin is produced within the melanocyte packaged into mealnosomes and distributed to the epithelial cells. Melanin is responsible for the coloring of the eyes, hair and skin. Melanin’s primary function is that of protection from UV light and preventing exposure and therefore limiting damage of UV light to the deeper tissues.
Langerhans cells are migrant cells that form an important immune function within the epidermis. Langerhans cells can be found between epithelial cells of the epidermis and are white lymphocytes. Langerhans cells migrate via the lymphatics and are significant cell in the presence of skin allergy. Langerhan cells are susceptible to UV light which can suppress the skins immune function.
The natural moisturizing factor (NMF)
The natural moisturizing factor is a complex process involving many different elements. Think of it as a glue like substance capable of holding the corneocytes of the stratum corneum together and providing protection. The production of the natural moisturizing factor begins in the stratum basale and makes it way up through the layers undergoing changes. I like to think of it beginning in the stratum basale where the cells are like moist juicy plump grapes and as those cells make their way up through the epidermis the cells become filled with keratin protein and the moisture like substance instead of being inside the cell surrounds the outside of the cell as it reaches the stratum corneum – forming the glue like substance of the NMF.
The acid mantle is a vitally important protective mechanism for the skin and its integrity should be preserved as much as possible. With the acid mantle intact the PH level of the skin varies between 4.5 and 5.5 ph making it slightly acidic.
The acid mantle is an invisible barrier produced by moisture from the eccrine sweat glands and sebum from the sebaceous glands. The primary purpose of the acid mantle is to prevent the invasion of bacteria which is alkaline in nature.