Chapter 36: Human Integumentary System
The skin is composed of two main layers: the epidermis and the dermis. The subcutaneous layer is often included in describing the structure of the skin, but is technically not part of the skin.
- Epidermis: this is the uppermost layer of the skin and is composed mostly of dead cells. It consists of three sub-layers called the cornified layer, granular layer and Malpighian layer.
– Cornified layer: consists entirely of dead cells that are brushed off continuously. Acts as the primary barrier to the outside world.
– Granular layer: consists of cells filled with the strong protein keratin.
– Malpighian layer: consists of a layer of cells called melanocytes – which are responsible for producing melanin (brown pigment in skin). They also produce the rest of the cells that make up the granular and cornified layers.
- Dermis: this layer is just below the epidermis and contains all of the organs of the skin, such as capillaries and blood vessels, nerve endings, various sense organs, sebaceous glands and hair follicles. It is also rich in collagen and elastin. This helps to give skin its strength and elasticity.
- Subcutaneous layer (hypodermis): is located below the dermis and is composed of cells filled with fat. This layer contains the adipose tissue. Sunlight action on this layer is responsible for producing vitamin D that the body can use in the digestive system to absorb calcium from food.
Functions of the skin
- Protection – acts as a physical barrier preventing entry of pathogens
- Excretion – excretes water, salts and a very small amount of urea
- Temperature regulation:
- Goose bumps (see picture below) are visible and hairs stand on end (due to contraction of the piloerector muscle) and vasoconstriction occurs when the body is cold.
- Sweat is produced, vasodilation occurs, and hairs lie flat when the body is hot
- Fat storage – adipose tissue just below the skin stores fat and acts as an insulator
- Sense organ – sense organs such as temperature and pain receptors send signals to the brain when stimulated
- Production of vitamin D – sunlight action on the fatty tissue within the skin causes the production of vitamin D, which is needed to absorb calcium from the digestive system