skin

• skin- primary organ of the integumentary system and is the largest organ of the body
• skin- continuous sheet of cutaneous membrane and forms the outer protective covering of the body
• the superficial layer is a sheet of keratinized squamous epithelium called the epidermis
• stratum basale- deepest stratum of the epidermis
• stratum basale- consists of a single sheet of columnar cells that continue to divide
• stratum spinosum- has a multilayer of distorted cells
• stratum basale and stratum spinosum together are often called stratum germinativum
• stratum granulosum- superficial to stratum spinosum
• stratum granulosum- contains flattened cells pushed up from the deeper strata and as the cells are pushed up through this stratum, they form protein granules
• stratum lucidum- meaning light layer
• stratum lucidum- very thin layer present only in the thick skin which is found only in high-wear areas like the palms and soles.
• stratum lucidum- translucent allowing light to pass through it easily
• stratum corneum- layer of dead keratinized tissue
• stratum corneum- extremely thick in thick skin, providing a great deal of protection. It protects deeper tissues from mechanical injury, the inward or outward diffusion of water and other molecules and invasion by microorganisms
• dermis- sheet of irregular fibrous connective tissue and much thicker than epidermis
• dermis- contains blood vessels, nerves, hair follicles, sweat glands, sebaceous glands, lymphatic capillaries, and collagen and elastic fibers.
• sensations are mediated by dermal nerve endings
• reticular layer- a thick region of irregularly arranged protein fibers. Most of the fibers are collagenous but few are made of elastin
• papillary layer- bumpy superficial portion of the dermis attached to epidermis.
• The bumps papillae (meaning nipples) form regular rows of thick skin but are irregularly shaped in the thin skin. This causes the skin to have distinct ridges like the fingerprints.
• ridges- give the hand and the feet better gripping ability
• deep to the skin is a layer of subcutaneous tissue called hypodermis or superficial fascia which is not actually part of the skin
• hypodermis/superficial fascia - contains fat cells, blood vessels, lymphatic vessels, nerves, and connective tissues that anchor the skin to underlying structures.
• subcutaneous tissue- loose fibrous connective tissue that connects the skin to underlying muscles and bones. Some of the areolar tissue is modified to become adipose tissue
• both hair and nails are modified forms of stratum corneum or keratinized tissue
• hair- cylinder compact keratinized material
• nail- plate of compact keratinized material
• each hair is formed within a separate hair follicle
• follicle- sheath-like indentation of the epidermis
• hair papilla- found at the bottom of the follicle, covered with stratum germinativum, produces the hair
• hair root- portion of each hair within the follicle
• hair shaft- portion that has been pushed out of the follicle
• exocrine sebaceous gland- attached to each follicle that produces fatty sebum that coats the hair and skin
• sebum- prevents moisture loss and conditions the hair and the skin so that they do not become brittle and easily broken
• arrector pili muscle- a strap of smooth muscle connecting the side of the follicle to the superficial surface of the dermis. When contracted, the muscle pulls the follicle so that it is perpendicular to the skin's surface.
• toenail or fingernail- formed by a modified portion of stratum germinativum which is called the matrix
• matrix- portion of the nail bed that produces the nail plate
• part of the matrix may be visible through the nail as a pale crescent or lunula
• nail formation begins under the fold of epidermis
• root- the portion of the nail under the fold