Structure of a Section through the Skin

The skin is the largest organ in the human body which provides a protective barrier against physical injury, pathogens, and harmful ultraviolet radiation.
It consists of two main layers: the epidermis (outside layer) and the dermis (inside layer). Beneath the dermis, there is a layer of subcutaneous fat tissue.
The epidermis is made up of 95% keratinocytes which create keratin, a protein that strengthens the skin. It does not have any blood vessels and get nutrients by diffusion from the dermis.
The stratum corneum is the outermost layer of the epidermis. It consists of dead keratinised cells and sheds regularly.
Adjacent to the stratum corneum is the rest of the epidermis, including the stratum basale, which contains stem cells that constantly divide and replenish the skin cells.
Melanocytes, found in the lower part of the epidermis, produce melanin, the pigment that gives skin its colour and protects it from UV radiation.
The dermis contains blood vessels, sweat glands, sebaceous (oil) glands, nerve endings, and hair follicles.
Sweat glands produce sweat which helps to control body temperature by evaporating from the skin surface causing cooling.
Sebaceous glands produce sebum, an oil that helps to keep the skin moist and provides a barrier against bacteria and fungi.
Hair follicles embedded in the dermis produce hair, which helps with the sensation and protection.
An intricate network of nerve endings and receptors in the dermis allows the skin to sense touch, pressure, pain, and temperature.
The fatty subcutaneous layer (also called the hypodermis) underneath the dermis provides insulation and cushioning for the body. It also serves as a storage area for fat, which can be used as an energy source.
When the body is too hot, blood vessels in the dermis dilate (vasodilation) allowing more heat to be lost from the skin. When the body is too cold, these vessels constrict (vasoconstriction), reducing heat loss.
When it is hot, sweat is produced from sweat glands to help cool down the body through the process of evaporation.
Another function of the skin is to synthesise Vitamin D when exposed to sunlight, which is essential for bone health.