Skin: The Ultimate Shield of Human Body.

Skin is the largest organ of the human body which weighs 16% of total body weight and covers 1.5-2 m2 of surface area. It is the basic unit of the integumentary system. Eyelids are the thinnest layer of skin which is about 0.5 millimetre and feet are the thickest layer which is about 4 millimetres.

The skin is made of three layers which are Epidermis- the outermost layer of skin, Dermis- the middle layer of skin, and Hypodermis- the innermost layer of skin.

The epidermis, protective outermost layer of the skin and contain five layers. It is composed of dead cells which are filled with keratin protein that have migrated outward from the basal layer which is next to the Dermis. The dead cells or keratinocytes are replaced every four weeks. The Epidermis has no blood vessel and the melanocytes- which are responsible for skin colour- mainly found in the Epidermis.

The dermis, the thicker and deeper layer of skin made up of connective tissue. The connective tissues are mainly made of collagen fibre which is acted like a bullet-proof jacket. It contains nerves that provide heat, pain, cold, and pressure to the brain.

The hypodermis, the innermost layer contains the adipocytes, fibroblasts, and macrophage etc. It serves to connect the skin with the fibrous tissue of the bones and muscles.

The skin provides many functions such are-

• Barrier function: Protection of underlying tissues and organs against impact, abrasion, fluid loss, and chemical and microbial attack.
• Thermoregulation: Maintenance of normal body temperature through sweat glands.
• Chemical synthesis: Synthesis of vitamin D3, important to normal calcium ion absorption. Production of melanin, which protects underlying tissue from ultraviolet (UV) radiation. Production of keratin, which protects against abrasion and repels water. Sensation: Detection of touch, pressure, pain, vibration, and temperature. Storage: Store lipids in adipocytes. Excretion: Excretes salt, water, and organic wastes.

There are two types of exocrine glands in the skin.  Sweat gland - produces sweat which helps the body to cool down. When the temperature is high outside the body, this gland secrets the sweat. Then the sweat evaporates in the air atmosphere and the body temperature goes down. When you are cold, the tiny muscle called arrector pili to cause hair to stand upright across the body. This phenomenon is called ‘goosebumps’ and it traps the body heat close to the skin.  Ceruminous gland - a type of sweat gland and secrets cerumen. The cerumen is also called ear wax which keeps the eardrum pliable, lubricates and clean the ear canal.  Sebaceous gland - secrets sebum for keeping the hair and skin lubricates.

There are some types of cell in the skin.  Markel cell - they are responsible for sensation like pressure, temperature etc.  Keratinocyte - the dead cells filled with keratin protein which are responsible for making epidermis, hair, and nail.  Langerhans cell - the tissue-resident macrophage, usually they are belonging to the immune cell which acts as Closed-Circuit Camera. They always monitor the pathogen in the skin, if they select the pathogen then catch the pathogen for submitting to T-cell to kill the pathogen.  Melanocytes - which are responsible for producing melanin. Melanin is called skin pigment which protects the skin from UV rays. UV-rays cause to damage the DNA of Melanocyte. Therefore, mutation of DNA happens and cause Melanoma- a type of skin cancer. Two types of melanin are produced from Melanocytes one is  Eumelanin - responsible for black skin and another is  Pheomelanin - responsible for reddish-brown colour.