Skin: Layers, Structure and Function

Skin

Skin, the body’s largest organ, comprises water, protein, lipids, and minerals. Your skin controls body temperature, guards against infections, and provides nerve endings, allowing people to sense their environment.

You can feel feelings like heat and cold because of your skin nerves. The integumentary system comprises sweat glands, oil glands, hair, and skin.

On average, six hundred fifty sweat glands, 20 blood arteries, and more than 1,000 nerve endings can be found in a square inch of skin. Even though it is only a few millimetres thick, the skin accounts for about one-seventh of a person’s overall weight.

What are the layers of the skin? 

Depending on how you count them, there can be one or more skin layers. The epidermis, dermis, and hypodermis (subcutaneous tissue) are the three primary layers of your skin. There are more layers within these layers. The skin has eight or ten layers if you count the layers within layers. The epidermis, dermis, and hypodermis are the three primary layers of the skin.

Epidermis – Top layer of the skin

The top layer is called the epidermis. Skin tone is a waterproof barrier that protects the skin. Its primary functions include producing fresh skin cells, producing skin colour, and shielding the body from ultraviolet (UV) radiation, pathogens such as fungi, viruses, bacteria, and harmful chemicals.

Each day, humans lose about 500 million skin cells. In actuality, the outermost layers of the epidermis are made up of 20–30 layers of dead cells. In its lower layers, the epidermis constantly produces new cells. These cells move to the surface over four weeks, harden, and replace the dead, shedding cells.

The most prevalent kind of cells in the epidermis are keratinocytes. 

Some of the diseases and conditions that affect the epidermis include:

• Acne
• Eczema
• Boils
• Melanoma
• Dandruff

The epidermis contains five sub-layers.

Stratum Corneum

The epidermis’ top layer is known as the stratum corneum. Its duties include:

• Aids in moisture retention for skin
• Keep harmful toxins away from your body.
• It is composed of keratinocytes, dead, flattened cells that are lost every two weeks. The fibrous protein keratin, produced by keratinocytes, gives your skin, hair, and nails structure.

Stratum Lucidum

The stratum lucidum, a separate layer, is only present in the thicker epidermis of the palms and soles of the hands and feet.

Its cells and functions are integrated into other layers in thinner locations. Its functions include :

• Enables skin to stretch 
• Protects your palms and soles from the impacts of friction while containing a protein that speeds up the ageing process of skin cells
• Waterproofs your skin
• Additionally, dead, flattened keratinocytes make up this layer.

Stratum granulosum 

Keratinocytes are slowly pushed towards the skin’s surface from the stratum granulosum layer. As they progress through this layer, cells lose their shape and characteristics, resembling the flattened, dead keratinocytes of the outermost layers more and more.

Lipids, a type of fatty acid, are also present in this skin layer and help create a waterproof barrier that stops your body from losing fluid through the skin.

Stratum Spinosum 

The layer of squamous cells known as the stratum spinosum is the epidermis’ thickest layer. It includes:

• Freshly developed keratinocytes
• Langerhans cells that aid in infection eradication

This primary barrier prevents foreign environmental elements from entering your body.

Stratum basale

The stratum basale, the basal cell layer, is the epidermis’ bottom layer. It includes several significant cell types, including:

• Older keratinocytes are propelled towards the surface by column-shaped stem cells, where they flatten and degenerate. 
• Melanocytes are the cells that give colour to your skin. 
• Merkel cells are the touch receptors.

Conditions involved in the epidermis

Both genetics and outside factors that affect this skin’s outermost layer cause it to age. These include drinking too much alcohol, smoking, and being exposed to too much UV light. These things cause wrinkles, sun spots, and uneven skin thickness or thinning.

Rashes and blisters, brought on by everything from infections and allergies to diseases and toxins, can also develop in the epidermis. In addition, it is where melanoma and non-melanoma skin malignancies first appear and where several dermatological signs of conditions, including diabetes and lupus, might appear.

Infections that the body can typically fight off can be brought on by epidermal penetration. These include illnesses brought on by insect or animal bites and germs that enter the body through open wounds, cuts, abrasions, or injuries from needlesticks. 

Dermis – Middle layer of skin

The middle layer of the skin is called the dermis. It has capillaries, nerve endings, connective tissue, and hair follicles. It also has several glands, such as apocrine glands that create sweat and sebaceous glands that produce sebum (a body oil). It plays several important roles, such as: 

Produces oil – The sebaceous glands produce sebum or oil. Sebum conditions the skin and hair while preventing bacterial growth on the skin. A pimple forms when the follicle that houses the sebaceous glands gets clogged with too much oil or dead skin cells.

Giving the skin support to maintain its shape –The dermal layer, which functions similarly to a building’s foundation, controls the skin’s turgor.

Blood distribution –Dermal veins nourish the skin, eliminate toxins, and deliver blood to the epidermis.

Growing hair –In the dermis are the hair follicles. Arrector pili muscles, affixed to each follicle root, contract when the body is chilly or alarmed, giving goosebumps.

Feeling – The dermis is rich in nerve endings communicating pain, itchiness, and pleasure to the brain.

 Disorders and conditions that affect the dermis layer include:

• Genetic collagen disorders such as Marfan syndromes and Ehlers-Danlos 
• Tumors, such as dermatofibrosarcoma protuberans
• Hives (urticaria)
• Chronic sun damage (solar elastosis)
• Autoimmune collagen disorders such as scleroderma

Papillary dermis

The thin top layer known as the papillary dermis is home to capillaries, tiny blood vessels that help control skin temperature and feed the epidermis with nutrients.

Additionally, this skin layer includes the following:

• Meissner corpuscles are sensors that convey subtle touch sensations.
• Lamellar corpuscles are sensors that communicate pressure and vibrational sensations.

Reciprocal Dermis

The reticular dermis is the lower, thicker layer with connective tissues and dense collagen bundles. The primary protein that gives skin and connective tissues structure is collagen. It makes skin more robust and more elastic.

The dermis has a different thickness depending on the body. It is around 0.6 millimetres thick on the eyelids. It is 3 millimetres wide and appears on the back, palms of the hands, and bottoms of the feet.

Conditions involved in the dermis

The dermis performs intricate duties and maintains constant contact and communication with the epidermis, controlling critical bodily systems.

The dermis is influenced by cells in the epidermis, controlled by cells in the epidermis (via the actions of cells like mast cells, which secrete cytokines). In other cases, like psoriasis, the relationship between these two layers is most affected.

As people age, less collagen is produced, causing the dermal layer to grow thinner. Just like the elastic waistband of a pair of shorts may lose its elasticity, elastin ages and becomes less flexible. This is what causes sagging and wrinkles.

Ageing is characterised by dry skin because the sebaceous glands and sweat glands generate less sebum and less sweat, respectively. Additionally, there is less surface area or contact between the dermis and epidermis. This reduces the amount of blood that can flow from the dermis to the epidermis and the amount of nutrients that can reach this outer layer of skin.

Hypodermis – Innermost layer of the skin

The hypodermis is the skin’s deepest layer. It is sometimes referred to as subcutaneous tissue and mainly consists of:

• Fat
• Connective tissues with fat
• Large blood vessels 
• Nerves

The subcutaneous layer is where most of your body fat is kept. It shields your muscles and internal organs against impacts and falls and insulates you from temperature changes.

SQ stands for subcutaneous in medical shorthand. A subcutaneous layer injection is administered. Along with these other functions, the hypodermis layer:

• It has fat cells kept for energy reserves.
• Enables the body to seem smooth and sculpted.
• Regulates temperature by causing blood vessels to constrict and expand.
• Serves as the skin’s site of attachment for bones, muscles, and other organs.
• It has the presence of deep pressure sensors.
• Produces the hormone leptin, which aids in maintaining the body’s metabolism in homeostasis (the proper balance of all of your body’s systems for optimal performance).

Conditions involved in the hypodermis

Ageing also decreases subcutaneous tissue, reducing sweating and making staying cool in hot weather more challenging. Additionally, it may influence how the body responds to drugs absorbed through subcutaneous tissue.

Even though the hypodermis isn’t visible, it can significantly impact how the skin ages and looks, particularly on the face and neck.

A person’s facial fat volume declines as they age, and there is less supporting tissue to maintain the skin’s natural flexibility. The muscles and bones of the face lose volume, and the facial skin starts to sag and droop. Some people may use Chemical cosmetic fillers to “plump up” the skin in these areas.

Conditions and disorders affecting skin

As the body’s external protection system, your skin might be at risk for various problems. These include: 

• Blisters
• Allergies like contact dermatitis and poison ivy rashes.
• Wounds, burns (including sunburns) and scars.
• Bug bites, such as tick, spider, and mosquito bites.
• Skin rashes and dry skin.
• Skin lesions, such as freckles, moles, and skin tags.
• Skin cancer, including melanoma.
• Skin infections 
• Skin disorders like eczema, acne, psoriasis and vitiligo.

How do I take care of my skin? 

As you get older, you might lose elastin and collagen. The dermis, the middle layer of skin, thins as a result. The skin might sag and become wrinkled as a result. While you cannot stop the ageing process, you can try taking specific steps:

• If you spend most of the day indoors, use sunscreen daily. One of the best options is to use a sunscreen with A broad spectrum with an SPF of at least 30.
• Don’t sunbathe either inside or outside. Skin damage results from tanning and leads to skin cancer and skin ageing.
• Find effective stress-reduction techniques. Stress can cause some skin conditions to get worse.
• Quit smoking and using tobacco products. Nicotine and other chemicals in electronic cigarettes and cigarettes cause the skin to age more quickly.
• Regularly check your moles and skin for any changes that could be signs of skin cancer.
• Wash your face gently both in the morning and at night.
• Apply moisturiser after each shower to avoid dry skin.

Summary 

Skin, the largest organ in your body, is critical in protecting your body from viruses and the weather. It controls your body’s temperature and gives you a feeling of touch thanks to nerves placed below the skin.

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