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Skin

Definition

The outer layer covering the body.

It is the largest organ of the integumentary system.

The skin has up to seven layers of ectodermal tissue that guards the underlying muscles, bones, ligaments and internal organs.[1]

Human skin is similar to that of most other mammals.

Though nearly all human skin is covered with hair follicles, it can appear hairless.

There are two general types of skin, hairy and glabrous skin (hairless).[2] The adjective cutaneous literally means “of the skin” (from Latin cutis, skin).

Function

Skin plays an important immunity role in protecting the body against pathogens[3] and excessive water loss.[4]

Its other functions are insulation, temperature regulation, sensation, synthesis of vitamin D, and the protection of vitamin B folates.

Severely damaged skin will try to heal by forming discolored and depigmented.scar tissue.

In humans, skin pigmentation varies among populations, and skin type can range from dry to oily.

Such skin variety provides a rich and diverse habitat for bacteria that number roughly 1000 species from 19 phyla, present on the human skin

Structure

Comprising three main layers of tissue:

  • The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone.
  • The dermis, underneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands.
  • The deeper subcutaneous tissue (hypodermis) consists of fat and connective tissue.

The skin’s color is created by special cells called melanocytes, which produce the pigment melanin. Melanocytes are located in the epidermis

The epidermis

the epidermis, an outermost layer that contains the primary protective structure, the stratum corneum;

The epidermis is layer consists of many special cells, including keratinocytes and melanocytes.

Keratinocytes are cells that make a special fat which gives skin it’s waterproof properties.

Melanocytes produce melanin, which is a pigment giving us the colour of our skin.

This layer is continuously shed and replaced, every 15–30 days.

The epidermis is sub-divided into 5 layers.

Stratum corneum

The outermost layer of the epidermis.

There are many cells which are tightly packed together

This allows the skin to be tough and waterproof.

This layer is important in the prevention of invasion from foreign things, such as bugs and bacteria.

Stratum lucidum

This layer contains several clear and flat dead cells.

It is a tough layer and is found in thickened skin, including the palms of the hand and soles of the feet.

Stratum granulosum

The stratum granulosum is composed of 3 to 4 layers of cells.

Keratin a colourless protein which is important for skin strength.is formed here.

Stratum spinosum

This layer contains cells that change shape from columnar to polygonal.

Keratin is also produced here.

Stratum basale

This layer is the deepest layer of the epidermis, in which many cells are active and dividing.

Melanocytes

melanocytes produce the pigment melanin which is responsible for the skin color of an individual.

Those with larger amounts of melanin in their skin have darker skin, or their skin darkens with more exposure to sunlight.

as the sunlight hits your skin, the light rays stimulate the production of melanin by melanocytes. Since the majority of melanin is called eumelanin, which is a brownish black color, your skin begins to darken as more melanin is produced protecting you against UV rays.

Keratinocytes

The keratinocytes actually originate in the stratum basale, but as they mature and age, they move from the deepest to the most superficial layer of the epidermis and eventually die in order to comprise the majority of the stratum corneum..

Once the really old keratinocytes reach the stratum corneum, they are known as ‘corneocytes.’ The corneocytes are basically the cells that are shed off your skin and become part of the dust floating around you.

keratinocytes do play a lot of important roles. One of these roles actually involves the melanin produced by melanocytes.

The keratinocytes take up and store some of the melanin produced by the melanocytes,

gives your skin an extra layer of protection from the damaging ultraviolet radiation of the sun’s light rays

Merkel cells

Merkel cells, which are cells that are important in the sensation of touch.

The stratum basale is separated from the next layer – the dermis – by a basement membrane, which is a layer made of collagen and proteins.

The Dermis

The dermis is the second major layer of the skin.

a fibrous layer that supports and strengthens the epidermis;

It is a thick layer made up of strong connective tissues.

It is further divided into two levels:

  • the upper is made of loose connective tissue, called the papillary region,
  • the lower layer is made of tissue that is more closely packed, called the reticular layer.

The dermis is made up of a matrix of collagen, elastin and network of capillaries and nerves.

The collagen gives the skin its strength, the elastin maintains its elasticity and the capillary network supplies nutrients to the different layers of the skin.

The dermis also contains a number of specialised cells and structures.

These include: hair follicles, sweat glands, sebaceous glands (produce sebum which helps lubricate skin & hair) and nails.

Apocrine glands, which develop during puberty, produce a scented sweat linked to sexual attraction that can also cause body odor, especially around the armpits.

It also plays an important part in controlling our skin temperature and acts as a cushion against mechanical injury.

When injured the dermis heals through the formation of granulation tissue (a tissue rich in new blood vessels and many different cells).

This tissue helps pull the edges of a cut or wound back together.

It takes our body from 3 days to 3 weeks to form this tissue.

The Hypodermis

Also known as the subcutis

a subcutaneous layer of fat beneath the dermis

supplies nutrients to the other two layers and as a fuel reserve in case of food shortage.

works as insulation and cushions us from knocks and falls.

 

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