I am the largest organ and also the one and only organ in the human body which is constantly exposed to the external environment! I am a waterproof, flexible, tough protective covering for you. My surface is smooth with only with hair and pores for sweat.

Without the mighty me, life on earth is impossible! Imagine your bones, muscles and organs flying all over the place! =( However, with me, you are ensured that your body would be intact and everything would be held together! I also protect your organs, muscles, nerves, and blood vessels against trauma! Certainly, palms of the hands and soles of the feet require greater protection too!

Other than holding everything intact, I provide a barrier to the environment, protect you from ultraviolet light, regulate your body temperature, senses touch, provides insulation to keep you warm!

However I can become infected with bacteria, viruses and fungi as well. Chemicals or other substances can also harm me!

My body has three main layers, namely the epidermis (the outer thinner layer), dermis (the middle thicker layer), and fats (the innermost layer). Let me introduce the three layers of me to you right now!

The epidermis is the relatively thin, tough, outer layer. The cells here originate from cells in the deepest layer of the epidermis called the Malpighian layer. They slowly move up toward the surface of the epidermis. Once they reach the surface, I would have to say goodbye to them by shedding them =( as the younger ones are pushing up from below.

The outermost portion of the epidermis, the granular layer, is waterproof and prevents nasty bacteria, viruses, and other foreign substances from entering the body! But if an evil person cuts my granular layer, you could be exposed to the nasty bacteria and viruses! =( To prevent infections, you must take good care of me!

Scattered throughout the Malpighian layer are cells called melanocytes, which produce the melanin. Melanin filters out harmful UV rays from sunlight, which can damage your DNA and cause you to have skin cancer (oh no!).

Langerhans' cells are part of my immune system and are present in the epidermis. They help me to detect foreign substances and defend you against infection but they could be bad guys at times and I will develop skin allergies. =(

Next, let me tell you more about the dermis!

The dermis, another layer of me, is thick and houses fibrous and elastic tissue that gives me my flexibility and strength. It is rich in nerve endings, sweat glands, sebaceous glands, hair follicles, and blood vessels.

The nerve endings (modified dendrites of sensory neurons) or sensory receptors sense pain, touch, pressure, and temperature (thermoreceptors). Some areas of me contain more nerve endings than others! For example, your fingertips and toes certainly have many nerves and are extremely sensitive to touch!

The sweat glands produce sweat in response to heat and stress. They are coiled tubes formed by a downward growth of the epidermis. It forms a tight knot in the dermis and is richly surrounded by blood capillaries. The sweat flows through the sweat duct and a sweat pore to the skin surface.

Sweat is composed of water, sodium chloride and small amounts of urea. Since sweat contains metabolic waste products, I am also considered an excretory organ!

Sweat is secreted continuously and the amount of sweat produced varies. They may even be produced in such little quantities that they evaporate immediately. When more sweat is produced, they appear as droplets on me. As sweat evaporates off the skin, it helps cool you down and regulates your temperature.

Specialised sweat glands in armpits and in genital regions (or the apocrine sweat glands) secrete a thick, oily sweat that produces a characteristic odor when the sweat is digested by the bacteria.

The sebaceous glands secrete sebum into hair follicles. Sebum is an oil pigment that keeps me moist and soft and acts as a barrier against foreign substances.

Hair contributes to your appearance but can regulate body temperature, provide protection and prevent injury, and enhance sensation as well! Although hairs are embedded in the dermis, they are produced by the epidermis. The Malpighian layer of the epidermis sinks into the dermis, forming a hollow tube, the hair follicle. The hair follicles produce the various types of hair found throughout the body. At the base of the follicle, there is a mass of tissue containing blood capillaries and nerves, the hair papilla. The hair papilla is covered with epidermal cells which constantly divide, pushing new cells upwards. They will soon die and harden, forming your hair!

The hair erector muscles are attached to the hair follicles. These muscles are capable of contraction, causing the hairs to stand on their ends and parts of me around the hair to be raised, producing the “goose pimples” of you!

The blood vessels of the dermis provide nutrients to me and help regulate your bodily temperature. The arterioles that carry blood to the capillaries here are controlled by vasomotor nerves. These useful vasomotor nerves bring about the reflex contraction and dilation of the arterioles, which makes me turn red and flushed when you are hot and after vigorous activities, or pale when you are scared or cold. Thus, they regulate bodily temperature.

When your temperature rises, my arterioles will dilate to allow more blood to flow through the capillaries in me. More heat is lost through me, by radiation, conduction and convection. The shunt vessels constrict and more blood enters the capillaries, increasing the amount of heat loss.

My sweat glands will start to be active and increase the production of sweat. As sweat evaporates, more latent heat of vapourisation is removed from you and this is really an efficient way of losing heat.

When your temperature begins to fall, the opposite occurs. Reflex constriction of the skin arterioles occurs and less blood flows through the blood capillaries, therefore less heat is lost by convection, radiation and conduction. The shunt vessels dilate and result in less blood flow to me. More blood is returned to capillaries in the deeper parts of me. Less heat is lost and heat is conserved.

Over different parts of the body, the number of nerve endings, sweat glands and sebaceous glands, hair follicles, and blood vessels varies. The top of your head has many hair follicles whereas the soles of your feet have none! (Imagine hairy legs and hands XD)

Next up is my sub-cutaneous fat layer! The fat layer is just below the dermis and it helps insulate you from heat and cold by providing protection. The fat is housed in living adipose cells, which are held together by fibrous tissue. The fat layer varies well! There is only very little fat cells on the eyelids, while there are several inches on your abdomen and buttocks!

Well, I hope that after you heard my introduction, I got a better idea of who I am and how important I am to you now!

Bye for now!

Love,

Skin(:

(Sinhui)