Anatomy of Your Skin & Some of its Properties
The skin is made of three layers:
The outer layer is called the epidermis and the middle layer is called the dermis. Beneath the dermis is the subcutaneous fatty layer (adipose tissue).
The epidermis is avascular, i.e. it contains no blood vessels.
The epidermis (or cuticle) of most of our skin is made up of 4 layers:
- the stratum corneum
- the stratum granulosum
- the stratum spinosum
- the stratum basale.
In the palms of our hands and the soles of our feet, we have an additional layer, the stratum lucidum. Of these layers, the 2 most important of are the stratum corneum (horny layer) and the stratum basale (basal layer).
The horny layer consists of dead, flattened cells. These cells are constantly being shed and replaced by cells from deeper layers. The cells in the basal layer are continually dividing to produce new cells. The old cells are pushed up to the horny layer where they become flatter, die and become part of the horny layer.
The dermis: The dermis or cutis (True Skin) is a highly sensitive and vascular layer that contains:
- Sweat glands: These glands produce sweat, which evaporates to cool you down if you get too hot.
- Sebaceous glands: These glands produce an oily substance called sebum. This keeps the skin moist, supple and waterproof. It also stops the hairs from becoming brittle.
- Hairs: Hairs grow from pits in the dermis called hair follicles. When the body gets cold the hairs stand on end and act as an insulator to keep you warm.
- Sensory nerves: Sensory nerves in the dermis allow you to detect temperature, pressure and pain.
- Blood vessels: Blood is carried from the heart to the skin by arteries. It is then returned to the heart by veins.
The subcutaneous tissue: The subcutaneous tissue consists of a fatty and muscular layer, including loose connective tissue, lymphatic, circulatory and nervous networks.
The skin’s proteins:
Collagen is the most abundant protein in the skin. Collagen fibers make up 75 percent of your skin. This is also your fountain of youth, for it’s responsible for warding off wrinkles and fine lines. Over time, environmental factors and aging diminish your body’s ability to produce collagen.
Elastin is a protein associated with collagen in the dermis. It’s another protein, responsible for giving structure to your skin and organs. As with collagen, elastin is affected by time and the elements. Diminished levels of this protein cause your skin to wrinkle and sag.
Keratin is the dominant protein in your skin, making up hair, nails and the surface layer of the skin, the stratum corneum. Keratin is what gives the rigidity and form to your skin.
Skin - facts & properties
The skin is the largest organ of the human body with several important functions to perform. It covers an average area between 0.7 to 1.5 square metres. Skin covers the entire body. Its depth varies, being thinnest on the eyelid and thickest on the palms of the hand and the soles of the feet.
The skin of the palms of our hands and the soles of our feet have an extra layer on the epidermis, the stratum lucidum.
Skin continually renews itself. Old skin cells are gradually shed and replaced by new ones, on average every 28 days.
Our skin is “almost completely… but not quite waterproof”, though it is referred to as our natural raincoat.
It stores water and fats and regulates our temperature. Though it is equally highly permeable to any solution that it is exposed to.
This apparent paradox can be clarified very simply: the exchange of body fluids on your skin in controlled by the lipid bi-layer and by special glands that regulate the uptake or loss of fluids.
As lipids do not mix with water, they provide a barrier for this exchange, but if the lipid bi-layer that forms the cell membranes is compromised, the barrier action diminishes. So, the cell membranes become more floppy and water trapped in between the cells is lost to the environment.
This is easily observed, if our skin is immersed in water for extensive periods of time, as the integrity of the bi-layer is affected and the skin gets wrinkled, e.g. if you have been in the water for too long.
Thus, extensive exposure of your skin to a solution will affect the by so called impermeability property of your skin. But, this controlled permeability can be used to our advantage by reversing a direction of the exchange.
This is the rationale for using hydrating solutions, creams and lotions on our skin. With the latter, we facilitate the nourishing of the lipid bi-layer with exogenous lipids (oils and butters) and support the regenerative process that leads to maintaining the integrity of our skin.
Like most of the body, skin contains a high percentage of water, approximately 40-50%. As it is exposed to the sun and wind, the skin is at more risk of drying out than any other parts of the body.
Therefore, it is important to keep the skin moisturized and to drink plenty of water to maintain a healthy skin.