Integument Is composed of skin and its appendages, sweat glands, sebaceous glands, hair and nails. Skin is classified according to the thickness of the epidermis into: 1.Thick skin (palms and soles) ( µm). It contains the 5 layers of cells but lacks hair follicles, arrector pili muscles and sebaceous glands. 2.Thin skin covers most of the reminder of the body (75-150µm), has thin stratum corneum and lacks stratum lucidum and granulosum. It has hair follicles, arrector pili muscles,, sebaceous glands and sweat glands.

Skin Is composed of: A- Epidermis (stratified squamous keratinized epithelium). B- Dermis (dense irregular collagenous CT.). The interface between them is formed by dermal ridges (papillae) that interdigitate with epidermal ridges. The two types of ridges are called rete apparatus. The hypodermis (superficial fascia) (is not a part of skin), a loose CT. with fat.

Thick skin Thin skin

Epidermis It is mm in thickness (thicker in palms and soles). The stratified squamous keratinized epithelium of skin is formed of 4 types of cells: 1.Keratinocytes. 2.Melanocytes. 3.Langerhans cells. 4.Merkel cells

keratinocytes Are arranged into 5 layers, they are continually renewed by mitotic activity of the basal layer of the epidermis. Toward the surface the cells accumulate keratin filaments. The 5 layers are: 1.Stratum basale (germinativum) 2.Stratum spinosum 3.Stratum granulosum 4.Stratum lucidum 5.Stratum corneum

Stratum basale (germinativum) It is the (deepest) germinal layer that undergoes mitosis, forms interdigitations with the dermis and is separated from it by basement membrane. It is formed of a single layer of cuboidal to columnar cells that have basophilic cytoplasm that has tonofilaments and large nucleus. They have desmosomes and hemidesmosomes.

Stratum spinosum Is the thickest layer that is formed of several layers of polyhedral to flattened cells. The most basal layer shows mitotic activity (together with the str. Basale are sometimes called malpighian layer).They are rich in tonofilaments (cytokeratin) than str.basalis.Tonofilament radiate outward through the processes toward adjacent cells forming inter-cellular bridges. The most superficial layers show more bundles of tonofilaments (tonofibrils) causing the cytoplasm to be eosinophilic. Their cytoplasm contain membrane-coating granules (lamellar granules) that contain lipid.

Stratum basale and spinosum

Stratum spinosum

Stratum granulosum Is formed of 3-5 layers of flattened keratinocytes (the most superficial layer that still possess nuclei). Their cytoplasm is rich in coarse, irregular basophilic kratohyaline not membrane bound granules, but they have membrane bound granules that release lipid-rich substance.

Stratum lucidum Is the clear, homogenous, lightly staining thin layer of cells above str. Granulosum. Is present only in thick skin. Its cells lack organelles and nuclei but they contain eleidin (packed keratin filaments)

Stratum corneum Is the most superficial layer, formed of numerous layers of flattened, keratinized cells with thickened plasmalemma. Its cells lack nuclei and organelles but are filled with keratin filaments. The far cells from the skin surface display desmosomes, while those near to the surface (squames or horny cells) lose desmosomes.

Non-keratinocytes in the epidermis I-Langerhans (dendretic) cells, are antigen presenting cells located among the cells of str. Spinosum. They have multiple long processes, dense nucleus and pale cytoplasm. They have no intermediate filaments but contain lysosomes and membrane bound Birkeck granules. They are a part of mononuclear phagocyte system. They are immune cells

II-Merkel cells Are scattered among str. Basale and serve as mechanoreceptors but they extend their processes between keratinocytes to which they are attached by desmosomes. The nuclei are indented. The basale lamina of the cells have unmeylinated sensory nerves to approximate the Merkels cells forming Merkel cell-neurite complexes.

III-Melanocytes Are derived from neural crest cells, located among cells of str. Basale and the superficial portion of the dermis. They are round to columnar cells. Their long processes penetrate the intercellular spaces of str.spinosum. They contain melanosomes that leave melanocytes through the processes, penetrate the cytoplasm of str.spinosum cells. Melanosomes contain tyrosinase enzyme that change tyrosine into melanin.

Melanocyte

Dermis (corium) Is formed of 2 layers: 1.Papillary layer, is composed of loose CT.that interdigitate with epidrmis forming dermal papillae or ridges. Its collagen type III and elastic fibers form network, while anchoring fibers (type VII)extends from the basal lamina into the papillary layer. It contains fibrobalsts, plasma cells, mast cells, and other CT.cells, capillary loops, and Meissner corpuscles. 2.Reticular layer, is continuous with papillary layer. It contains dense irregular T., thick type I collagen and elastic fibers. It contains sweat glands, sebaceous glands, hair follicles and smooth muscle cells and pacinian and Ruffini corpuscles

Epidermis-dermis interface It presents parallel primary dermal ridges, on its surface separated by primary grooves that house projections of the epidermis. Also in the center of each dermal ridge is a secondary groove which receive down growth of the epidermis (inter-papillary peg), along these ridges are dermal papillae

Glands of the skin I-Eccrine sweat glands, are located in the skin throughout most of the body. They are simple coiled tubular glands (merocrine), located deep in the dermis or hypodermis. The secretory unit is formed of cuboidal to columnar cells which are: a.Dark cells, are mucus-secreting cells (contain granules). b.Clear cells, are water-secreting cells and do not have granules. *They have myoepithelial cells. Their ducts are composed of stratified cuboidal epithelium.

II –Apocrine sweat glands, are found in certain regions as axilla, areola of the nipple and anal region. They are larger than eccrine glands. Their ducts open into canals of the hair follicles not into the surface of skin as eccrine glands. Their secretory cells are cuboidal to columnar and have myoepithelial cells. The glands have wide lumen. They are under the influnce of sex hormones so they appear after puberty

III-Sebaceous glands, are embedded in the dermis and hypodermis and secrete sebum. Their ducts open into the hair follicles. They are lobular with clusters of acini opening into single short ducts. Each acinus is composed of peripheral located small basal cells, which surrounded large round cells. Their ducts are lined by stratified squamous epithelium.

The hair follicle Is formed of: a.Hair root (Has matrix that acts as str.basale). With the dermal papilla forms hair pulp b. Mid-shaft that is formed of medulla, cortex, cuticle, internal root sheath, external root sheath and glassy membrane. c. Shaft of the hair that extends through the surface.

Hair follicles

Finger nail Is formed of: 1.Nail plate (hard keratin) 2.Nail bed (epidermis under the nail plate). 3.Nail matrix (from the nail root) that proliferate to form nail plate.

Thick skin Thin skin Practical slides