Skin is the largest organ in the body. It covers the body's entire external surface, serving as a first-order barrier against pathogens, UV light, and chemicals, and provides a mechanical barrier to injury. It also regulates temperature and amount of water released into the environment.
Layers of Epidermis
Cells of the Epidermis
It consists of two layers of connective tissue which merge together, no clear demarcation.
The dermis houses the skin appendages (sweat glands and hairs), many sensory neurons, and blood vessels.
Also called subcutaneous fascia,
The skin has multiple functions including:
The embryology of the skin includes:
Blood flow to the skin is a very effective mechanism for heat transfer from the body to the environment, which is controlled by the autonomic nervous system. Increase in body temperature will cause vasodilation of skin blood vessels. This dilation is caused by inhibition of the sympathetic centers in the posterior hypothalamus (that control blood vessel tone), to increase heat loss from the body. Decreased body temperature will cause vasoconstriction of skin blood vessels throughout the body. This vasoconstriction is caused by stimulation of the posterior hypothalamic sympathetic centers to decrease heat loss from the body.
Free Nerve Endings
Arrector Pili Muscle
Skin is continuously shed/desquamated in the following sequence:
Langer’s Lines: The collage and elastic fibers in the reticular dermis form regular lines of tension in the skin. If the skin incisions are made along these lines, less scarring will occur.
Skin is divided into multiple areas called dermatomes. There are 30 dermatomes on the body. They are numbered according to the level of spinal vertebral from which they arise. There are seven cervicals, 12 thoracics, five lumbar, and five sacral. Certain diseases like shingles have symptoms that involve a dermatome pattern. Also, dermatomes help to diagnose the level of vertebral spinal injury.
Epidermal water barrier established by: