Human Skin!

The skin is the outer covering of the body and is the largest organ of the human body. Also called the integumentary system, it is made up of multiple layers of epithelial tissues, and guards the underlying muscles, bones, ligaments and organs. It is classified as an organ because it consists of various tissues that are joined to perform specific actions. On average, there is approximately 22 square feet (1.9 m2) of human skin, which weighs approximately 12 pounds.
Because it interfaces with the environment, skin plays a very important role in protecting the body against pathogens. Its other functions are insulation, temperature regulation, sensation, and the synthesis of vitamins. Severely damaged skin will try to heal by forming scar tissue. Scar tissue is often discolored, appearing with a different pigment, and lacking in elasticity. In Latin, the word cutaneous translates to “of the skin”.
Remember, all Anatomy and Physiology can be broken down into two general categories, Structure and Function.
Functions of the Skin 1.    Protection. The skin is a barrier against the outside world. It is almost completely
waterproof, and it provides a mechanical cushion against injury to delicate structures inside.
2.    Sensation. The skin is a sensory organ. Sensations of touch, heat, cold, and pain are moderated through the skin.
3.    Temperature regulation. The sweat glands and arterioles work together to rid the body of excess heat or to conserve body heat when necessary.
4.    Vitamin D synthesis. Exposure to sunlight causes the skin to synthesize vitamin D. 5.    Absorption, secretion, excretion, and respiration. The skin plays a minor role in
the functions of absorption, secretion, excretion and respiration.

Structure of the Skin
The skin is basically composed of two layers. The external layer is called the epidermis and the internal layer is called the dermis. The epidermis is “cemented” to the dermis by a “muco protein cement substance.” The dermis is connected to underlying structures by bands of connective tissue fibers.
Epidermis
The epidermis consists of two, three, or four strata, depending on which part of the body is examined. The deepest portion of the epidermis, the portion cemented to the dermis, contains a single sheet of epithelial cells and melanocytes. The layers of epidermis are all avascular. These epithelial cells divide and reproduce themselves in the stratum germinativum, (“germinate”).
Melanocytes produce melanin, the substance that gives color to the skin, and is also a protection against harmful UV rays of the sun.
Cells created in the stratum germinativum slowly travel toward the external environment. As they progress, they die and undergo a process called keratinization. This means that the living matter of the cell is replaced by keratin, a specialized protein. Since keratin is repellent to water, the dead cells filled with keratin form a solid protection against water.
The outermost layer of the epidermis, the stratum corneum, is made up of 10 to 20 layers of keratinized epithelial cells, firmly cemented together. The outermost layers flake off at the same rate as new cells are being produced in the stratum germinativum.
Dermis
The dermis is usually described as having two regions. The superficial region is called the papillary layer. Papillae are protrusions that indent into the epidermis, and they often contain sensory nerve endings.
The deeper region of the dermis is called the reticular layer (meaning network). It is basically a network of strands of connective tissue filled with “ground substance,” a gel (hyaluronic acid) that is semi solid. The dermis has arteries, arterioles,veins, venules, capillaries, and lymphatics (vascular). The epidermis has no blood or lymph supply at all (avascular).

The Hypodermis
The hypodermis (subcutaneous layer, or superficial fascia) lies between the dermis and underlying tissues and organs. It consists of mostly adipose tissue and is the storage site of most body fat. It serves to fasten the skin to the underlying surface, while providing thermal insulation, and shock absorbency of impacts to the skin.
Other than humans, the only other mammals that carry a protective layer of adipose tissue in the hypodermic layer are seafaring ones like dolphins, whales, and seals.

ASIS Promoting Peace, One Body at a Time

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