An Introduction to human skin

         

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    What is the Human Skin???

Ever wondered what is your skin?? The human skin is the outer covering of the body and is one of the largest organ in the body. The skin has up to seven layers of ectodermal tissue and guards the underlying muscles, bones, ligaments and internal organs.It covers your whole body and makes up about 16 percent of your overall body mass.

Skin layers

The skin has three basic levels — the epidermis, the dermis, and the hypodermis:

Epidermis

Main roles: makes new skin cells, gives skin its colour, protects the body.The epidermis is the outermost layer; it is a waterproof barrier that gives skin its tone.Dead cells are shed continuously from the epidermis as new ones take their place.We shed around 500 million skin cells each day. In fact, the outermost parts of the epidermis consist of 25–30 layers of dead cells.

New cells are made in the lower layers of the epidermis. Over the course of around 4 weeks, they make their way to the surface, become hard, and replace the dead cells as they are shed.Keratinocytes are the most common cell type within the epidermis; their job is to act as a barrier against bacteria, parasites, fungi, viruses, heat, ultraviolet (UV) rays from the sun, and water loss.The epidermis contains no blood vessels.

The colour of our skin is produced by a pigment called melanin, which is produced by melanocytes; these are found in the epidermis and protect the skin from UV rays.

The epidermis is subdivided into five layers:

stratum corneum

stratum lucidum

stratum granulosum

stratum spinosum

stratum germinativum

Between the epidermis and the dermis is a thin sheet of fibers called the basement membrane.

Dermis

Main roles: makes sweat and oil, provides sensations and blood to the skin, grows hair.

The dermis is mostly connective tissue, and it protects the body from stress and strain; it gives the skin strength and elasticity. If the dermis is stretched a lot, for instance, during pregnancy, the dermis can be torn, and this shows up as so-called stretch marks.

Receptors that detect pressure (mechanoreceptors), pain (nociceptors), and heat (thermoreceptors) are based in the dermis.

The dermis houses hair follicles, blood vessels, and lymphatic vessels. It is also home to a number of glands, including sweat glands and sebaceous glands, which produce sebum, an oil that lubricates and waterproofs hair.

The dermis is further split into two layers:

Papillary region: made of loose connective tissue, it has finger-like projections that push into the epidermis. These projections give the dermis a bumpy surface and are responsible for the patterns we have on our fingertips.

Reticular region: made of dense, irregularly organized connective tissue. Protein fibers in the reticular region give skin its strength and elasticity.

Subcutaneous tissue

Main roles: attaches dermis to the body, controls body temperature, stores fat.

The deepest layer is called subcutaneous tissue, the hypodermis, or subcutis. It is not technically part of the skin but helps attach the skin to underlying bone and muscle. Subcutaneous tissue also provides skin with nerves and blood supply.

The hypodermis is mostly made of fat, connective tissue, and elastin (an elastic protein that helps tissues return to their normal shape after stretching). The high levels of fat help insulate the body and prevent us from losing too much heat. The fat layer also acts as protection, padding our bones and muscles.

Some hormones are made by fat cells in the hypodermis, vitamin D, for instance.