What is our skin? Mammalian skin often contains hairs, which in sufficient density is called fur. The hair mainly serves to augment the insulation the skin provides, but can also serve as a secondary sexual characteristic or as camouflage. On some animals the skin is very hard and thick, and can be processed to create leather. Reptiles and fish have hard protective scales on their skin for protection, and birds have hard feathers, all made of tough β-keratins. Amphibian skin is not a strong barrier to passage of chemicals. A frog sitting in an anesthetic solution will quickly go to sleep. The outermost epidermis is consists of stratified squamous epithelium with an underlying basement membrane. It contains no blood vessels, and is nourished by diffusion from the dermis. The main type of cells which make up the epidermis are keratinocytes, with melanocytes and Langerhans cells also present. The epidermis can be further subdivided into the following strata (beginning with the outermost layer): corneum, lucidum, granulosum, spinosum, basale. Cells are formed through mitosis at the innermost layers. They move up the strata changing shape and composition as they differentiate, inducing expression of new types of keratin genes. They eventually reach the corneum and become sloughed off (desquamation). This process is called keratinization and takes place within about 30 days. This layer of skin is responsible for keeping water in the body and keeping other harmful chemicals and pathogens out. Blood capillaries are found beneath the epidermis, and are linked to an arteriole and a venule. Arterial shunt vessels may bypass the network in ears, the nose and fingertips. The dermis lies below the epidermis and contains a number of structures including blood vessels, nerves, hair follicles, smooth muscle, glands and lymphatic tissue. It consists of loose connective tissue otherwise called areolar connective tissue - collagen, elastin and reticular fibres are present. Erector muscles, attached between the hair papilla and epidermis, can contract, resulting in the hair fibre pulled upright and consequentially goose bumps. The hypodermis is not part of the skin, and lies below the dermis. Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. It consists of loose connective tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes (the hypodermis contains 50% of body fat). Fat serves as padding and insulation for the body. The skin must be regularly cleaned. Unless enough care is taken it will become cracked or inflamed. Unclean skin favors the development of pathogenic organisms. The constantly peeling off dead cells of the epidermis mix with the secretions of the sweat and sebaceous glands and the dust found on the skin to form a filthy layer on its surface. If not washed away the dirt and dead skin slurry begins to decompose emitting a foul smell.
Definition interpretationAcne
- An inflammatory disease of the sebaceous glands and hair follicles of the skin that is marked by the eruption of pimples or pustules, especially on the face.
Bacteria
- Microscopic unicellular prokaryotic organisms characterized by the lack of a membrane-bound nucleus and membrane-bound organelles.
Dermis
- The sensitive connective tissue layer of the skin located below the epidermis, containing nerve endings, sweat and sebaceous glands, and blood and lymph vessels.
Epidermis
- The outer, protective, nonvascular layer of the skin of vertebrates, covering the dermis.
Hypodermis
- A subcutaneous layer of loose connective tissue containing a varying number of fat cells.
Pimples
- A small swelling of the skin, usually caused by acne; a papule or pustule.
Ultraviolet radiation
- Invisible electromagnetic radiation between visible violet light and X rays.
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