Ea - 5Th Ch - Integumentary System

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Integumentary System

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Consists of the skin (cutaneous membrane consisting of epidermis and dermis) and its derivatives (nails, hair, sweat glands, and sebaceous glands).

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Layers of the Epidermis from deep to superficial.

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Stratum Basale, stratum spinosum, stratum granulosum, stratum lucidum (only in thick skin), and the stratum corneum. The 1st 3 strata are composed of living keratinocytes, and the last 2 strata contain dead keratinocytes.

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Stratum Basale

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The deepest epidermal layer. Aka the stratum germinativum or basal layer. a single layer of cells ranging from cuboidal to low columnar. Tightly attached to underlying basement membrane. Contains 3 types of cells: keratinocytes, melanocytes, and tactile cells.

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Keratinocytes

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The most abundant type of cell in the epidermis and are found throughout the epidermal strata. Play a role in synthesis of the protein keratin.

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Melanocytes

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Have long branching cytoplasmic processes and are scattered among the keratinocytes of the stratum basale layer. Transfer pigment granules, called melanosomes into the keratinocytes within the basal layer and sometimes within more superficial layers.

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Tactile Cells

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Few in number and found scattered among the cells within the stratum basale. Sensitive to touch, and when compressed, they release chemicals that stimulate sensory nerve endings, providing info about objects touching skin.

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Stratum Spinosum

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Found superficial to the stratum basale layer of the epidermis. Formed by several layers of polygonal keratinocytes. Attach to eachother by many intercellular junctions called desmosomes. Also contains the fourth epidermal cell type, the epidermal dendritic cells (immune cells that help fight infection in the epidermis).

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Stratum Granulosum

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'Granular Layer' consisting of 3-5 layers of keratinocytes supterficial to the stratum spinosum. Within this stratum begins the process of keratinization by which the keratinocytes fill up with the protein keratin.

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Stratum Lucidum

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This so called "clear layer" is a thin, translucent region about 2-3 squamous cell layers thick that is superficial to the stratum granulosum. Found only in thick skin. Cells occupying this layer appear pale and featureless, and have indistinct boundaries and anucleate keratinocytes.

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Stratum Corneum

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The most superficial layer of the epidermis. Consists of about 20-30 layers of dead, scaly, interlocking keratinized, squamous cells called corneocytes. The dead cells are anucleate (lacking a nucleus) and tightly packed together.

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Thick Skin

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Found on the palms of the hands, the soles of the feet, and fingers and toes. Contains sweat glands, but no hair follicles or sebaceous glands.

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Thin Skin

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Lacks the Stratum Lucidum. Contains hair follicles, sebaceous glands, and sweat glands.

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Melanin

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A pigment produced and stored in melanocytes. Synthesized from the amino acid tyrosine. Malanin is transferred in membrane-bound vesicles from melanocytes to keratinocytes in the stratum basale. Darker-skinned people have melanocytes that produce relatively more melanin than do those of lighter-skinned individuals.

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Dermis

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Lies deep to the epidermis and is composed of cells of the CT Proper and primarily of collagen fibers, although both elastic and reticular fibers are present. Found in the dermis are blood vessels, sweat glands, sebaceous glands, hair folliclles, nail roots, sensory nerve endings, and smooth muscle tissue. 2 major regions of dermis = superficial papillary layer and a deeper reticular layer.

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Papillary Layer

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The superficial region of the dermis directly adjacent to the epidermis. Composed of areolar CT. Region of the dermal papillae.

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Dermal Papillae

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Projections of the dermis toward the epidermis. Interlocks with deep profections of epidermis called epidermal ridges. Contains the capillaries that supply nutrients to the cells of the epidermis, and sensory receptors that monitor touch on the surface of the epidermis.

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Reticular Layer

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Forms the deeper, major portion of the dermis and extends from the thin, overlying papillary layer to the underlying subcutaneous layer. Consists primarily of dense irregular connective tissue through which large bundles of collagen fibers project in all directions.

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Subcutaneous Layer

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Deep to the integument. Also called the hypodermis. Not part of the integument. Consists of both areolar CT and adipose CT. Functions to pad and protect the body as well as acting as an energy reservoir, and provides thermal insulations.

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Nails

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Are hard derivatives from the stratum corneum layer of the epidermis. The cells that form the nails are densely packed and filled with parallel fibers of hard keratin.