An Overview Of Human Skin
The Glands Of The Epidermis, Dermis And Subcutaneous Layers Of Skin
Jun 19, 2009
The skin is largest organ of the body and protects internal organs against external elements. Bacteria or viruses cannot penetrate an intact skin barrier, although they can enter via small abrasions and some may enter via the respiratory system.
In addition to its role as a barrier, the skin also deals with pathogens using chemical defenses, such as the sweat glands producing a pH level to make the skin uninhabitable for many microbes. Saliva, tears and mucous secretions also ‘wash’ away many unwanted microbes. Nerve receptors in the skin also allow the body to sense heat, cold, pressure, pain and touch.
The Three Layers Of The Skin
The three layers of the skin are epidermis, dermis and subcutaneous layer.
The Epidermis: Epidermis is comprised mostly of cells called keratinocytes. The epidermis has five layers within its structure.
- Stratum basale or stratum germinativum: the basal layer where the renewal of skin begins.
- Stratum spinosum: comprised of cells with spiny projections.
- Stratum granulosum: the site of keratin production.
- Stratum lucidum: this is a keratin-rich layer usually found in the palms of hands or soles of feet.
- Stratum corneum: the outermost layer comprised of dead cells that shed and are replaced by cells from the layers beneath.
Dermis: the dermis is the inner layer of the skin. It is comprised of collagen and elastin fibers interwoven with blood vessels, nerves and fat lobules. The dermis also has finger-like projections called papillae that extend to the epidermis.
Subcutaneous layer: the subcutaneous layer lies underneath the dermis. This layer is mostly comprised of fat and serves to insulate the body from extremes of temperature. It also contains connective tissue and a small amount of blood vessels.
Hair Follicles, Sweat Glands And Sebaceous Glands
Hair: hair covers the skin and the root of hairs sit in follicles in the dermis. Blood is supplied to the hair and follicle via a papilla. Each hair follicle has a muscle attached called and erector pili which makes the hair stand erect to provide insulation when it is cold. To read more about this physiological adaptation in humans and other animals see Why Do Humans And Animals Get Goosebumps.
Sweat glands: there are two types of sweat glands found in skin. These are eccine glands and apocine glands.
- Eccine glands: the eccine glands are found all over the body except for the lips and around external genitalia. The eccine glands secrete sweat through pores on the skin surface when the body becomes overheated or heat affected due to stress. As sweat evaporates and as air passes over the sweated skin, this helps cool the body.
- Apocine glands: apocine glands secrete into hair follicles rather then skin surface and can be found in armpits and pubic region.
Resource and further reading:
Campbell and Reece, 2002, 'The Body’s Defenses', in Biology 6th edition, ed. Benjamin Cummings, San Francisco, chap 43.
