The integumentary system is the largest organ in the body and accounts for 8-15% of a person’s body weight. It must be tough to protect us but supple so that we can move and stretch.
The epidermis is the outer layer of skin. The majority of cells (95%) are specialised epithelial cells called keratinocytes which produce a tough protein called keratin. There are five distinct sub-layers of cells that represent the different stages in the keratinisation process. New skin cells are produced at the basal membrane (deepest epidermal layer) pushing the older cells towards the surface. As the keratinocytes get older and migrate closer to the skin's surface they change from being square-shaped to flat, they become engorged with keratin and eventually die, losing all of their internal structures. These overlapping, closely packed layers of keratinized cells form a permeable barrier and are able to withstand scuffs and scrapes. It takes 40-60 days for keratinocytes to reach the surface of the skin where they are sloughed away.
Other cells in the epidermis include melanocytes and Langerhans cells. Melanocytes are responsible for the surface colour of the skin, they produce melanin which protects the skin from UV radiation. Langerhans cells are part of the skin's immune response and engulf foreign material.
The epidermis does not contain any blood vessels but is nourished by the capillaries in the dermis below.
The dermis is much thicker than the epidermis and lies immediately underneath it. It is a collagen rich connective tissue that contains fibroblast cells that produce collagen and elastin, which are responsible for the pliability and strength of skin. It is connected below to the hypodermis. The dermis is made up of two layers, reticular (deeper) and papillary (superficial). The dermis contains the sensory nerve endings, hair follicles, arrector pili muscles, sweat glands, sebaceous glands, lymphatics and capillaries.
The hypodermis is not a skin layer but lies below the dermis, and is a subcutaneous tissue which contains fat, blood vessels and sensory receptors.
In summary;
Depth;
Burns can be classified as partial or full thickness burns, first, second or third degree burns.
Surface area;;
The skin has the following appendages;
Skin has several important functions;
It is very important to keep the core body temperature at a constant 37 degrees otherwise the bodies cells can not function properly. Sweat glands are present in the skin of the entire body, but are more frequent in the palms, soles, armpit, groin and forehead. Sweat is similar to blood plasma and consists of water, salts, and waste products such as urea. Sweat is forced to the skin surface where it immediately evaporates; this approximates to about 500-600 ml a day. When the body needs to lose more heat, such as when partaking in strenuous exercise, sweat is produced at higher rates.
The blood supply to the skin also plays an important role in thermoregulation. The capillaries to the skin in someone who is cold constrict, decreasing the blood flow and conserving heat. If a person is hot then the capillaries in the skin dilate, increasing the blood flow to the skin and allowing the loss of heat.
The skin has a variety of sensory receptors embedded in it. Touch receptors are found in the dermis and receptors for pain, heat, pressure and vibration are found in the dermis and hypodermis. Hair follicles have receptors that can detect the slight movement of a hair.
Sun exposure (UV) triggers the skin to produce vitamin D. Vitamin D is a hormone and is important in maintaining calcium blood levels.