Integument a.hair follicles b.arrector pili muscles Is composed of skin & its appendages, sweat glands, sebaceous glands, hair & nails. Its classified according to thickness of the epidermis: Thick skin (palms & soles) (400-600µm). It contains the 5 layers of cells but LACKS: a.hair follicles b.arrector pili muscles c.sebaceous glands. 2.Thin skin covers most of the reminder of the body (75-150µm), has thin stratum corneum & lacks stratum lucidum & granulosum. It has hair follicles, arrector pili muscles, sebaceous glands & sweat glands.

Skin Is composed of: A- Epidermis (stratified squamous keratinized epithelium). B- Dermis (dense irregular collagenous CT.[type 3 & 7 collagen]) The interface between them is formed by dermal ridges (papillae) that interdigitate with epidermal ridges. The 2 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 Keratinocytes. Melanocytes. Langerhans cells. Merkel cells It is 0.07-0.12mm in thickness (thicker in palms & soles). The stratified squamous keratinized epithelium of skin is formed of 4 types of cells: Keratinocytes. Melanocytes. Langerhans cells. Merkel cells Not in thin skin

keratinocytes The 5 layers are: Stratum basale (germinativum) 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: Stratum basale (germinativum) Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum Not in thin skin

Stratum basale (germinativum) It is the (deepest) germinal layer that undergoes mitosis, forms interdigitations with the dermis & is separated from it by basement membrane. It is formed of a: single layer of cuboidal to columnar cells basophilic cytoplasm tonofilaments & large nucleus desmosomes & 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. Tonofilaments radiate outward 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 oraganelles & nuclei but they contain eleidin (paked keratin filaments)

Stratum corneum Is the most superficial layer, formed of numerous layers of flattened, keratinized cells with thickened plasmalemma. Its cells lack nuclei & organelles but are filled with keratin filaments [ eleiden ] 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 antigen presenting cells located among the cells of str. Spinosum have multiple long processes dense nucleus & pale cytoplasm have no intermediate filaments but contain lysosomes & membrane bound Birkeck granules. part of mononuclear phagocyte system. are immune cells

Langerhans cells

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

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

Melanocyte

Dermis (corium) Is formed of 2 layers: Papillary layer, is composed of loose CT. that interdigitate with epidrmis forming dermal papillae or ridges. Its collagen type III & elastic fibers form network, while anchoring fibers (type 7)extends from the basal lamina into the papillary layer. It contains fibrobalsts, plasma cells, mast cells, & other CT.cells, capillry loops, & Meissner corpuscles. Reticular layer, is continuous with papillary layer. It containsdense irregular CT., thick type I collagen & elastic fibers. It contains sweat glands, sebaceous glands, hair follicles & smooth muscle cells, pacinian & 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: Dark cells, are mucus-secreting cells (contain granules). Clear cells, are water-secreting cells & do not have granules. *They have myoepithelial cells. Their ducts are composed of stratified cuboidal epithelium.

Eccrine (merocrine) sweat gland

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

III-Sebaceous glands, are embedded in the dermis and hypodermis secrete sebum ducts open into the hair follicles 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 ducts are lined by stratified squamous epithelium.

Sebaceous glands

The hair follicle Is formed of: 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 & external root sheath & glassy membrane. c. Shaft of the hair that extends through the surface.

Hair follicle

Hair follicles

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