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Structure and Functions of Skin

A skin layer called the epidermis lies on top, while a skin layer called the dermis lies on the bottom.
Structure of skin
In adults, the skin has a surface area of 1.5 to 2 m2, contains glands, hair, and nails, and is the largest organ in the body. A skin layer called the epidermis lies on top, while a skin layer called the dermis lies on the bottom. The skin and underlying structures are separated by a subcutaneous layer of adipose (fat) tissue and areolae.

A. Epidermis
Skin's epidermis is composed of keratinized squamous epithelium stratified into layers. The epidermis varies in thickness from one part of the body to another. Foot soles and palms have the thickest skin. Most epidermal cells are keratinocytes. Capillaries do not line the epidermis. The deeper layers receive a fluid that contains oxygen and nutrients from the dermis, but also drains away as lymph. The epidermis consists of many layers of cells (strata), starting from the deepest germinative layer to the ultra-thin stratum corneum (a thick layer of horny cells). squamous are thin, non-nucleated, dead cells consisting of keratin and other fibrous proteins in place of cytoplasm. The cells in the surface layer are constantly being rubbed away and replaced by those that originated in the germinative layer and have been subjected to gradual changes during their progression up to the surface. Approximately one month is required to replace the epidermis completely.

There are 6 parts in the epidermis of the skin that includes:
1. Stratum corneum (keratin)
The stratum corneum is an outermost layer of skin cells, which leave behind only keratin after they have died. In general, keratin protein is waterproof. We couldn't even take a shower without damaging our cells if our stratum corneum didn't provide a waterproof barrier. As well as protecting against pathogens, it also protects against chemicals. Most bacteria and microorganisms can't penetrate unbroken skin. Inhibitors such as fatty acids in sebum help remove microorganisms when dead skin cells are removed from the surface.
Functions - Water is prevented from entering or leaving, prevents pathogens and many chemicals from entering if unbroken.

2. Stratum germinativum (stratum basale)
Also known as stratum basale, stratum germinativum may be described in various ways. Dermis' interior layer, stratum germinativum, is where mitosis occurs. Cells are pushed to the surface as they are being replaced by new ones. Keratin is produced by these cells, which in turn die as they travel farther away from the dermal capillaries. In turn, cells in lower layers of the skin replace dead ones as they wear off.
Functions - In continuous mitosis, surface cells wear off and are replaced by new ones, Antimicrobial defensins are produced, and Vitamin D is produced when cholesterol is exposed to UV rays.

3. Langerhans cells
A Langerhans cell in the epidermis is also known as a dendritic cell due to its branched appearance when it moves. A certain amount of mobility is present in these cells, which originates from the red bone marrow. As a result of phagocytosis, bacteria that enter the body through breaks in the skin are destroyed. Langerhans cells present ingested pathogens to lymphocytes, the type of white blood cells, in lymph nodes when they are ingested by them. An immune response results in the creation of antibodies (antibodies are proteins that mark foreign substances for destruction).
Functions - Lymphocytes are stimulated to produce an immune response by phagocytizing foreign material.

4. Melanocytes
In addition to the melanocytes, the lower epidermis consists of other types of cells. A pigment called melanin is also produced by melanocytes. The number of melanocytes in individuals of similar size is similar, though the level of activity may differ. Melanocytes produce melanin continuously in dark-skinned individuals. Melanocytes from people with light skin produce less melanin. We are genetically predisposed to certain types of skin color because melanocytes are genetically regulated.
Functions - As a result of UV ray exposure, they produce melanin

5. Merkel cells
Functions - These are the receptors that tend to respond to touch.

6. Melanin
Functions -
Prevents the skin from being exposed to more UV rays.

B. Dermis
Unlike other types of fibrous connective tissue, the dermis consists of fibers arranged irregularly, so that they do not run parallel to each other. The dermis is strong and elastic. Both collagen and elastin are produced by the fibroblast. Elastic fibers can recoil after stretching, and collagen fibers are strong. Strength and elasticity characterize the dermis. Strain marks, also known as stretch marks, are caused by the tearing of the elastic fibers in the skin. This often occurs during pregnancy and in obese individuals. Water is absorbed by collagen fibers, which give the skin its tensile strength, but the tissue's tensile strength decreases with age, resulting in wrinkles. Macrophages, mast cells, and fibroblasts are the most common cells in the dermis. Areolar tissue and adipose tissue (fat) make up the deepest layer of the skin.

There are 8 parts in the dermis that include:
1. Papillary layer
A papillary layer is an uneven connection between the dermis and epidermis. It has an abundance of capillaries that nourish both the dermis and stratum germinativum.
Functions - The stratum germinativum is nourished by a dense layer of capillaries.

2. Hair (follicles)
Epidermal tissue makes up hair follicles, and they grow like that of the or arrector pili muscle. This muscle pulls the hair follicles upward when stimulated by emotions like fear or cold. This traps air and provides greater insulation for an animal with fur.
Functions - Dust is kept out of the eyes and nasal cavities by eyes and nasal cavities, A head's hair acts as an insulation against the cold.

3. Nails (follicles)
The nail follicles on the ends of the fingers and toes produce nails, just as the hair follicles do. At the base of the nail, during mitosis, new cells form (a form of keratin that is stronger than that found in hair) and die. Nail beds are typically formed of living epidermis and dermis, even though nails themselves are composed of keratinized dead cells. It is painful to cut a nail too short due to this reason.
Functions - To prevent mechanical injury to ends of fingers, and toes.

4. Receptors
Most sensory receptors in the dermis correspond to cutaneous senses (the Merkel cells are in the stratum germinativum, as are a few nerve endings). Pain, touch, pressure, heat, and cold are cutaneous senses. Sensations are detected by specific types of receptors, which are small structures that allow specific changes to be detected. Usually, nerve endings produce sensations including pain, heat, and cold. The sensory nerve endings that sense touch and pressure are encapsulated, which means that they have a cellular structure surrounding them
Functions - Perception of changes in temperature, pressure, hot, cold, and pain as cutaneous sensations.

5. Sebaceous glands
These ducts open either directly onto the skin or into the hair follicles of the sebaceous gland. The lipid substance they secrete is known as sebum, otherwise known as oil.
Functions - Produce sebum, which prevents skin and hair from drying and inhibits bacteria from growing.

6. Ceruminous glands
The ear canal is lined with these glands in the dermis. Cerumen or ear wax is the excretion (which contains sebum secreted in the ear canal).
Functions - Produces earwax, which prevents the eardrum from drying.

7. Eccrine sweat glands
The eccrine glands are found throughout the body, but they are particularly prominent on the forehead, upper lip, and palms, and soles. In these glands, the secretory portion is simply a tube coiled within the dermis. The tube has an opening on its surface that leads to a skin pore.
Functions - Excessive body heat causes sweat to evaporate, cooling the body.

8. Arterioles
Apart from capillaries, the arterioles are another extremely important blood vessel in the dermis. Unlike other kinds of arteries, arterioles are small and can be constrained (closed) or dilated (opened) by smooth muscles in their walls. Blood is important for maintaining body temperature since it carries heat, which is a form of energy.
Functions - When warm, dilate to lose more heat, During cold weather, the body contracts to conserve energy, Stress may cause blood vessels to constrict to divert blood to other organs.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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